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Question How to build a UHF antenna... ( AVS Forum HDTV Technical )
Updated: 2008-05-23 09:32:18 (751)
How to build a UHF antenna...

Found this site while researching antennas. Worked great for me. Check it out if you need a cheap UHF antenna.

http://uhfhdtvantenna.blogspot.com

Answers: How to build a UHF antenna... ( AVS Forum HDTV Technical )
How to build a UHF antenna...

Quote:
Originally Posted by tombobiche
I have some reflector material as in Don Bouldry's shown reflector thats galvinized, Ive read that 1" or 1X2" mesh is good, ; Id try that kind ; I also have 2X2" chicken wire. Normally I would have seperated the crossovers but the simple tape solution seemed allright. Actually some of your designs belong at Nasa really they are fine.
If you use chicken wire for the 4-bay the twists (and the wires that connect them) must be horizontal to be an effective reflector for the horizontal polarization of the antenna.

rabbit73

How to build a UHF antenna...

Quote:
Originally Posted by johnied

4.You could have two different towers on the same antenna farm
with different types of antennas and their directionality..






John
I have a question about directionality. Do most TV broadcast antenna's use a horizontal dipole, like what we use to receive the signal? If so, is it stronger perpendicular to the dipole as opposed to parallel, like a dipole is at reception?

Does the FCC store the directionality and type of antenna or is there some way to find this out? Does TVFool take this into account?

toastyfries

How to build a UHF antenna...

The FCC has antenna pattern and polarization for TV transmitters in its database. I know TV Fool takes the pattern into account; I do not know if it uses total power or only power received by a horizontally polarized antenna into account, however.

nybbler

How to build a UHF antenna...

Quote:
Originally Posted by toastyfries
I have a question about directionality. Do most TV broadcast antenna's use a horizontal dipole, like what we use to receive the signal? If so, is it stronger perpendicular to the dipole as opposed to parallel, like a dipole is at reception?

Does the FCC store the directionality and type of antenna or is there some way to find this out? Does TVFool take this into account?
They can do all sorts of things to change the pattern.. beam tilt for
example imagine tipping a flashlight up and the beam goes further out
but overshoots the area underneath.. just an example...



Actually if i recall on the FCC website you can do a TV station search and somewhere along the bottom when the stations info comes up there is map data not sure and like he said above tvfool has radiation patterns too.



If I find the link for the FCC i will repost it here by editing...


John

johnied

How to build a UHF antenna...

Quote:
Originally Posted by johnied
Actually if i recall on the FCC website you can do a TV station search and somewhere along the bottom when the stations info comes up there is map
data not sure and like he said above tvfool has radiation patterns too. If I find the link for the FCC i will repost it here by editing...
FCC TV Database Query:

http://www.fcc.gov/mb/video/tvq.html

If a station is directional, it will have a polar plot, for example:

http://www.fcc.gov/fcc-bin/polarplot...78&p360=0.822&

A question I have is how some stations can achieve a non-directional pattern (at least in the azimuth plane). If most signals are horizontally polarized, how can such elements radiate equally on the off-axis? I suppose they use arrays to compensate for this, but I would like to know more.

Falcon_77

How to build a UHF antenna...

Here are a few broadcast antenna white papers from Dielectric:
http://www.dielectric.com/broadcast/dtv.asp
You'll find that many "Omni" antennas have 1+ dB "fluctuations"....

holl_ands

How to build a UHF antenna...

I built one today from steel wire and wood based entirely on mclapp's excellent pdf dimensions; The steel was fairly malleable and seems to be some sort of stainless after cleaning. . The movie I was watching on Fox "Being Julia" was pulling about 19% with the 7X7", with the new 9 1/2 " I immedialy got 87%; I dont expect to have any more lost signals! Its behind the table with no reflector as can't fit fit in that spot. Ill test it on analogue for the weakest stations; but fundamentally is a complete success by my standards, so thankyou for all the advice, training , diagrams, pictures and material, to switching to a larger antenna for my area. Hope to install a mesh eventually as the summer progresses....

tombobiche

How to build a UHF antenna...

Quote:
Originally Posted by tombobiche
I built one today from steel wire and wood based entirely on mclapp's excellent pdf dimensions; The steel was fairly malleable and seems to be some sort of stainless after cleaning. . The movie I was watching on Fox "Being Julia" was pulling about 19% with the 7X7", with the new 9 1/2 " I immedialy got 87%; I dont expect to have any more lost signals! Its behind the table with no reflector as can't fit fit in that spot. Ill test it on analogue for the weakest stations; but fundamentally is a complete success by my standards, so thankyou for all the advice, training , diagrams, pictures and material, to switching to a larger antenna for my area. Hope to install a mesh eventually as the summer progresses....

I'm glad it worked out for you, I have had good success with these antennas and what's great is they inexpensive and fairly easy to build.

I'm now working on a new idea that was passed along to me by another forum member that looks very promising.

It has to do with the reflector spacing and my modeling shows a 2 db increase in net gain on VHF-hi with a possable slight increase in UHF as well over previous designs.

I liked the chicken wire feed horn antenna in one of your previous posts, imagine that on the roof of a condo.
I was able to read most of it, it would be interesting to know if it really works.

mclapp

How to build a UHF antenna...

I have another version of the horn thats only four feet tall that fits in an apartment attic. Since digital is different these seem the best antennas concievable, where the older ones may work best on analogue. I did try the log periodic, yagi and circular antennas without much success.
Im looking at your design now and as predicted it favors the UHF band when the smaller antenna will bypass the lower stations. Every station has a tendency to pull higher, so Im sure that ouside and even with the reflector it will even further surpass. Of course theres so many factors in material and construction vaying from your concept,and the dimensions are optimal.


Oh heres a better image of it


tombobiche

How to build a UHF antenna...

Here are the plots for the wires crossing in the middle with both sets of wires being bent away from each other where they cross the same amount.

mclapp

How to build a UHF antenna...

Here are the plots and diagram for the method I used which is similar to the factory designs.

mclapp

How to build a UHF antenna...

I have a question about the antennas y'all are building. They all seem to have the same length of "bowtie". Don't you want to have an array of different lengths to better capture different frequencies? Such as nearly 30" for channel 9 to around 8" for channel 49?

While I'm here, let me request some opinions for a new antenna system. I'm actually in a good signal area but in a lousy local situation because of large, old trees. My house itself cannot see in the direction of the towers so an attic, rooftop, or sidewall antenna is out of the question unless I go extremely high.

What I do have is the remains of an old dish system out in the yard, away from the house and underneath a huge old cedar tree. It's about 100 coax feet away from my TV. At this point there's a nice aperture that allows for a relatively clear shot at most of the transmitters. What I've been using the last 10 years is an array of twinlead dipoles hung up in this tree. A few of these dipoles covered the range between channels 3 and 55. This worked great for analog. No problems in the worst of wind and weather. I was able to watch the doppler radar on TV all night one night when we had winds that peaked out the wrong side of 135.

Now I'm going digital and there's no more low vhf to worry about but the old way isn't doing all that well. Most of the time I'm getting fine reception but when the weather gets bad, it goes down the tubes with a lot of dropouts, stuttering and pixellation.

Here's what I have to work with at my exact coordinates. I've also included the good weather signal strengths.

ch 17 at 9.4 miles/233? dBm -37.8 signal 87-97
ch 27 at 18.5 miles/269? dBm -44.8 signal 85-90
ch 9 at 16.6 miles/268? dBm -49.6 signal 85-90
ch 47 at 7.8 miles/222? dBm -45.8 signal 75-80
ch 31 at 7.8 miles/222? dBm -41.4 signal 90-95
ch 41 at 22.3 miles/264? dBm -60.3 signal 65-77
ch 45 at 7.7 miles/195? dBm -48.5 signal 82-87

What I've done is thin down to a 8?" dipole aimed at 265? and a 24" dipole aimed at 220?. Hanging dipoles don't work with digital. As an interim solution I have the two dipoles with opposing plain wire reflectors strapped to pvc pipes stuck in the tree. Great reception under ideal conditions but not stable enough for severe weather. After the changeover, we'll have one more on 25 @ 7.8 miles and 222?. Right now, 41 is the channel that gives me the most difficulty. There are other channels but I don't want them and have them blocked.

So anyway, I'm planning a better system and thinking about a single unit consisting of a grate/mesh reflector and bowties like you guys are building. Ideally this thing could be kept at a low altitude, like 10' or under.Do you have any recommendations for reflector and element sizes?

Don Bouldrey

How to build a UHF antenna...

Here are the models and pics of the 4 bay antenna I made recently. It uses 9 5/8" bay spacing with 9 3/4" wiskers.

The reflector is 40" tall and 36" wide the outside edges are bent forward about 2" on the ends and is spaced 5" back from the elements. The elements are also swept forward 2".

It seems to work pretty good, I get TV stations that both antenna web and TV fool don't even list for my location.

I also built a hoverman which worked pretty well on UHF but I need VHF-hi reception and the hoverman didn't work at all on VHF-hi (nor is it supposed to).

The 4 bay with the oversize reflector will get all the UHF & VHF-hi stations I have in my area with-in 40 mi. with solid signals.

mclapp

How to build a UHF antenna...

Here are the VHF-HI computer simulation models for for my 4 bay I described in an earlier post along with a picture of the crossover.

It's not a super VHF-hi antenna (nor should it be) but it gets the job done for me. Luckily the VHF-hi digital stations in my area are on ch. 7 & 8 where the models show that the SWR is somewhat reasonable. I do have a ch12 analog station 35mi. away through the hills and it also receives that very well.

I'm also going to include the VHF-hi computer models for a stock CM4221 to show the difference the larger reflector screen makes on a 4 bay.

Although it's not all the reflector, the antenna I built is also tuned for a lower frequency.

The models I have run show a similar improvement in a CM4221 with a larger reflector, just the curve is more towards the upper end of the VHF-hi instead of the lower end like the one I built.

mclapp

How to build a UHF antenna...

Thanks, mclapp. That was a lot to digest.

This seems to confirm my observations that the 4221 is better for 7 on the back-side than the front side. However, my custom built bow-ties are designed (hopefully) to have improved upper VHF reception. So far it seems to be working.

My 10" 2-bay UHF bow-tie is working well at the office. So the old balun must have been damaged in transit last time, when didn't work well here at all. It looks like I'm set to try 4 bays again...

Falcon_77

How to build a UHF antenna...

Thanks for all the posts you guys. I see some great ideas to try. And the fact that some baluns are failing gives me cause for concern. I will set up some kind of test antenna that makes it easy to test each one of mine. I'm going to be busy with other stuff for a while.

spokybob

How to build a UHF antenna...

Well after looking at the do-it-yourself options I found these two to be most stable. Duplicating a commercial antenna maybe good but usually the path of least resistance works best for me. Its nice to see all the gain from the balloon of electrons around the elements and reflector, so all the muscle work and theoretical sweat on the 9 incher wasn't wasted.
I built this from aluminum wire ; 7 and 7 as the DIY attic yagi; 1" gauge rusted chicken coop material 4.24" behind. Sitting on the table behind my Goldstar TV with Magnavox converter it pulled in about 12 new stations some running at over 85 percent for around 65 miles. No doubt hoisted on the 30 foot tepee pole with lightning arrestor it will hit 100 percent gain, and turned West will pull 125 miles on a good day.
It was helpful to understand that precise and equal cutting and placing of the elements increases performance.


tombobiche

How to build a UHF antenna...

Quote:
Originally Posted by tombobiche
...I built this from aluminum wire ; 7 and 7 as the DIY attic yagi; 1" gauge rusted chicken coop material 4.24" behind...
Are you saying you used 7" elements with 7" spacing?

girdnerg

How to build a UHF antenna...

Could you guys who have had success with your bowtie/youtube style antennas post the dimensions...

Thanks,
John

johnied

How to build a UHF antenna...

Quote:
Originally Posted by johnied
Could you guys who have had success with your bowtie/youtube style antennas post the dimensions...
My UHF bow-tie build is:

10" Element Lengths (each side)
10" Spacing between bays
1" Spacing between sides (this is too close, 1.5" would probably be better)
6" Whisker spread

This is optimized for the lower UHF band, but seems to work well enough into the 50's and 60's.

I'm still experimenting with this as my re-built 4-bay doesn't perform any better than the 2-bay version.

The Hoverman was easier to build, however. I used 7" for each segment and 6" for the horizontal portions.

See this post for pictures of each:

http://www.avsforum.com/avs-vb/showt...8#post13862508

Falcon_77

How to build a UHF antenna...

Try this link, and the post before it.
http://www.avsforum.com/avs-vb/showt...8#post13338498

It shows predictions and reception results for antenna scales from 87.5% to 125% (7" to 10") of the nominal CM4221 8" design, all but one with reflector. Only one point is out of line with predictions, and that could be a placement issue; I have a highly diffracted signal field, so there are local maxima and minima in my test area (aka family room).

I will note that several posters have reported differing results, a result, I believe, of the relatively complicated reception requirements of DTV - signal strength isn't all that important compared with s/n ratio and multipath interference.

I'll note my clones are all 9"/112.5%, and that the differences we're talking here - a few dB - are small compared with uncontrolled factors. I talked a little about that here:
http://www.avsforum.com/avs-vb/showt...4#post13816174

Frank

fbov

How to build a UHF antenna...

Wow, thanks guys.

Ill save this page..

The Hoverman is an odd looking animal how does that work in comparison to the 4 bay bowtie... Well never mind ill read up on it. :P


John

johnied

How to build a UHF antenna...

Quote:
Originally Posted by johnied
Wow, thanks guys.

Ill save this page..

The Hoverman is an odd looking animal how does that work in comparison to the 4 bay bowtie... Well never mind ill read up on it. :P


John

The Hoverman works good, so close to the 9" 4 bay on UHF that it would take some really good test equipment to tell the difference and It's much easier to build minus the reflector.
The only reason I didn't stick with the Hoverman I built was it's performance is way below the 4 bay in VHF-Hi band.
(as expected since its not designed for VHF-HI although neither is the 4 bay but it does work alittle)

mclapp

How to build a UHF antenna...

The Hoverman was weaker on my upper VHF tests, but does well enough on UHF to be a stand-in for my 4228. I currently have the 4228 and the Hoverman combined for UHF and a 30" bow-tie for VHF.

Combining the Hoverman and the 4228 has hardly made any difference, which surprised me. I expected the signals to drop as the Hoverman is in front of the 4228 and the coax feeds are of different lengths.

I think I will try the 4221 reflector on my 4-bay to see what it does. It's a bit small for my oversize build, however.

Falcon_77

How to build a UHF antenna...

Quote:
Originally Posted by Falcon_77
The Hoverman was weaker on my upper VHF tests, but does well enough on UHF to be a stand-in for my 4228. I currently have the 4228 and the Hoverman combined for UHF and a 30" bow-tie for VHF.

Combining the Hoverman and the 4228 has hardly made any difference, which surprised me. I expected the signals to drop as the Hoverman is in front of the 4228 and the coax feeds are of different lengths.

I think I will try the 4221 reflector on my 4-bay to see what it does. It's a bit small for my oversize build, however.
Does your Hoverman have the split screen reflector? I built mine with the split screen reflector. It outperforms the 4 bay without the screen reflector but not the 4 bay with the oversize bent screen reflector.

mclapp

How to build a UHF antenna...

Quote:
Originally Posted by mclapp
Does your Hoverman have the split screen reflector? I built mine with the split screen reflector. It outperforms the 4 bay without the screen reflector but not the 4 bay with the oversize bent screen reflector.
It doesn't have a reflector yet. All my builds thus far have been w/o them.

I built a 9" 2-bay tonight, which is performing better than the 10" 4-bay, but I will have to see if performance drops again when I up it to a 4-bay as well.

The Hoverman still seems to be the best I've made for UHF.

Falcon_77

How to build a UHF antenna...

I rebuilt the antenna using the DIY article with 7" element length and 7" spacing. I had tried the YouTube with 5 3/4" spacing and got worse results. The only thing is Ive read that coat hanger wire may surpass copper line so thats a thought. Removing the reflector helped on back stations, but on a couple of low broadcasters the reflector helped to zero in on that particular station.
Similiar to the channel master I left the bowties splayed instead of squashed , :allowing for the negative space bewteen the ears to lay symmetry to the positive space and Im thinking this helped to produce a friendlier electronic environment.
Lol those bulkier 2X4s arent the 1.5 X 3 I was using and that was a mistake, but spacing should be 1" between the small ends and 2" between the elements.
Id consider building the 8" 8" or the 9" 9" or even the Hoverman, but the DIY seems most useful.





tombobiche

How to build a UHF antenna...

The thought to build an 8 bay with this comes up. For sure twin lead is the best way to join them, and the distance between the two units should be correct although I dunno what that would be.Why there would be decreased performance from an 8 bay not sure Heres a pic of how I rigged an 8 bay over and under and spliced.... left side joins with left side; right side joins with right side


tombobiche

How to build a UHF antenna...

Attached are pictures of my latest 4-bay build, with 9" elements and spacing. Just to see what would happen, I tried leaving the feedlines straight all the way up and down. Let's just say there's a good reason to twist the top and the bottom, so don't try this at home.

The 2nd picture is what I have now and it finally performs better than the 2-bay version, but not by all that much.

I think I will be going back to 1x3's for the next build, as the extra inch in width for the 1x4's makes these rather bulky. I should be able to retain the 1.5" spacing on a 1x3.

Falcon_77

How to build a UHF antenna...

Quote:
Originally Posted by Falcon_77
Attached are pictures of my latest 4-bay build, with 9" elements and spacing. Just to see what would happen, I tried leaving the feedlines straight all the way up and down. Let's just say there's a good reason to twist the top and the bottom, so don't try this at home.

The 2nd picture is what I have now and it finally performs better than the 2-bay version, but not by all that much.

I think I will be going back to 1x3's for the next build, as the extra inch in width for the 1x4's makes these rather bulky. I should be able to retain the 1.5" spacing on a 1x3.
To anyone who doesn't know the twists put the top and bottom element of a 4 bay back in phase with the other two elements.You want all your sine waves on those elements to look alike.

johnied

How to build a UHF antenna...

this is something I can't answer on my own so Ill just ask. Element length be it 7", 8", 9", 10" has an effect on which end of the UHF band stations are recieved. What I think I read was that the 7" element will serve the high end of the UHF band best.
At TV Fool the Post Transition after Febuary '09 shows that channel 25 in my area (PBS) will be transmitting at 49.36 KW, Ive tried and I can't get this station even though its been reported to be up and running and will remain unchanged. Stations 49 miles away at 1000 KW (Fox) do come in; in analogue PBS comes in fine with an antenna but fuzzy at times. Channel 25(PBS Real 25, Virtual 24.1, 49.36Xmit, -103.5 dbm 49 miles away) is in Green and TV fool says it should be performing OK, I can't get it at all.
My question is, what would be the precise and best element length to recieve Channel 25 UHF dead on; and perhaps everything else from say 7 VHF up to 48 or 58 UHF?

tombobiche

How to build a UHF antenna...

It may be useful to bring this info forward to help answer your question. If you are having trouble with 25, try a 9" or 10" version.

Quote:
Originally Posted by fbov
The commercial design is an 8" element length and bay spacing. I set up a stand where I could vary the element spacing and length, and tested 7", 8", 9" and 10" antennas. This corresponds to peak gain channels of 88, 66, 51, and 40, respectively.
Which station is your PBS 25, I count 9 there for DTV now that will remain there.

Falcon_77

How to build a UHF antenna...

Attached are my results for the new 9" UHF bow-tie builds as compared to some earlier designs. The 9" version is working quite well, so I will probably try the 4221 reflector on it. Does it matter how far back the reflector is from the elements?

One thing I noticed is that Low-VHF reception went through the floor when I upped the 2-bay version to 4-bay. However, upper VHF reception remained largely unchanged (and probably good enough). I found that my TV can show AGC (Automatic Gain Control) figures for NTSC channels as well, so I'm using that for VHF going forward. A lower AGC figure is better (under ~45 is strong).

The UHF ATSC tests show SNR/AGC as before. The column 2nd from the right is the test with straight feedlines. Have a look at KPXN between that column and the far right column.

Falcon_77

How to build a UHF antenna...

Everything else being equal longer length for lower channels or frequency.

johnied

How to build a UHF antenna...

Quote:
Originally Posted by tombobiche
My question is, what would be the precise and best element length to recieve Channel 25 UHF dead on; and perhaps everything else from say 7 VHF up to 48 or 58 UHF?
I think you want to try a shorter element. Channel 25 is centered around 539 MHz, which gives it a wavelength of 55.66 cm, about 22 inches. You want each element to be 1/4 wavelength long, or about 5.5 inches.

olaf44

How to build a UHF antenna...

Thanks alot, I re-read everything and conculded I needed a longer element, but 9" and 10" are what I'll attempt. This is LPB (Louisianna Public Broadcasting) KLTS-DT from Shreveport. On analogue the new copper 7" was ganbusters and I was using 2 baluns on a twinlead back into the Goldstar UHF screw in which has never recieved that much gain from near the floor.
Theyre saying that currently KLTS is at 18 KW but projected to go up to 45 KW or so,; since I can't get it now Im hopeful, but in digital even 45KW is far below what many other stations barely scrape by at at 18% so Ill have to wait and see. I even emailed Beth Courtney to see if they'll keep it public lol. My coordinates are 32.50 lat 94.74 Long.
Ill look at some of the clones with near 10" spacing so thanks. Trying copper for the attic, maybe a mesh of some sort or none on it, all done on a hardwood floor plank.

On coordinates heres something I was doing in between paintings.

tombobiche

How to build a UHF antenna...


tombobiche

How to build a UHF antenna...

the one at 7" is racing pretty good, I may try the 5.5" spacing on the aluminum 2x4 I had built earlier.....

tombobiche

How to build a UHF antenna...

Quote:
Originally Posted by olaf44
I think you want to try a shorter element. Channel 25 is centered around 539 MHz, which gives it a wavelength of 55.66 cm, about 22 inches. You want each element to be 1/4 wavelength long, or about 5.5 inches.
1/4 is for a dipole or 1/2 for both sides.

Bow-ties are 1/2 wavelength on each element (each side) or a full wavelength for both sides.

Falcon_77

How to build a UHF antenna...

I was thinking about U-bolting the base of the 9.5 to the roof vent and using only twinlead and then a small balun on the end, the other model kind of balun. I read somewhere you can pack the terminal with aluminum foil and then seal it to have it stay fresh longer. Im wondering if a coat of sealer would hurt it once its assembled. Im also looking for a simple homade lighting arrestor if anyone has any ideas about that.
Well heres some plans I used for years which probably cant beat the 12 gauge dipoles but could be good for experimentation and dimensions and different design applications for compact models.
I was getting some stations from Dallas 125 mi from here after a storm, and the signal got so constant that the 7kw from the East was playing on digital over 50 mi away.

tombobiche

How to build a UHF antenna...

Quote:
Originally Posted by tombobiche
I'm also looking for a simple home made lighting arrestor if anyone has any ideas about that.


A couple of bucks at Radio Shack.

n4yqt

How to build a UHF antenna...

Quote:
Originally Posted by tombobiche
I was thinking about U-bolting the base of the 9.5 to the roof vent and using only twinlead and then a small balun on the end, the other model kind of balun.
...
Tom,
You might want to reconsider your mount and downlead.
- An antenna will put mechanical stresses on whatever it's attached to. Antenna masts, tripods, mounts, etc. are designed for the stresses. Plumbing vents aren't, they're not cheap to replace, and bad things can happen if they're damaged. I'd only use the roof vent for short-term testing, never a permanent installation.
- twinlead makes a better antenna than downlead, and that's especially important with DTV's sensitivity to multipath. Put the balun at the feed point and run RG6 from there or you may find you're better off without the antenna.

Frank

fbov

How to build a UHF antenna...

Ill try for the coaxial and feedpoint Balun for digital for sure



Thanks for the advice on the plumbing; I may construct a small tower of wood and stack an 8 bay from the 9.5" Im not sure an 8 bay would outperform the 9.5" 4 bay. Even the reflector for slight foward gain only on VHF I may stop short of but if its a night for day situation Ill attach the reflector as shown by mcclap's instructions and diagram, I could only find 2/2chcikenwire but may clip some mesh to that dimension, Im gonna get some coaxial and a new balun and lightning arrestor

tombobiche

How to build a UHF antenna...

Quote:
Originally Posted by tombobiche
Ill try for the coaxial and feedpoint Balun for digital for sure

Thanks for the advice on the plumbing; I may construct a small tower of wood and stack an 8 bay from the 9.5" Im not sure an 8 bay would outperform the 9.5" 4 bay. Even the reflector for slight foward gain only on VHF I may stop short of but if its a night for day situation Ill attach the reflector as shown by mcclap's instructions and diagram, I could only find 2/2chcikenwire but may clip some mesh to that dimension, Im gonna get some coaxial and a new balun and lightning arrestor

As fbov said use the balun at the feedpoint and run coax down, if possable run the feedline/balun 90 degrees from the feedpoint straight out the back.

The screen dimensions I posted, http://www.avsforum.com/avs-vb/attac...1&d=1211856836 when added to a non reflector 4 bay will out perform an 8 bay without a reflector.

It will increase the gain of a non reflector 4 bay by about 2 - 6 db net gain due to the improved reception pattern and better match with the feedline.

If done right it will be very noticable.

mclapp

How to build a UHF antenna...

thats awesome thanks mcclap for the shortcut. frankly I was leary of double stacking the 9.5" Ive built not only from weight but lack of funds to set up the baluns. So I'll try setting a reflector on the 4 bay, and keep one in the air, and the other behind the TV.
Its no problem switching the lines between electrical storms, I saw at Lowe's they have the cage wire for $19.95 which is pricey for overall; but a good investment for long term viewing. I bought 25 feet of RG6 and a good external balun at Lowes with a U-Crimp it included, which should be useful for arranging the setup. I agree fully that low loss in digital is vital to maintaining the signal.
They have a little booster at Lowes for $20. I think its one of those 25db boosters for split or extremely long lines so I steered clear of it; I just dont know if its the proper pre-amp, but thats pretty cheap for a 25 db signal amplifier on UHF. For now Ill stay with the mechanical approach; low loss with RG6 and new balun and screen on the 4 bay and the Tepee pole for now. I caulked and painted the base to the external one so any day I can screw in the bowties and work out the reflector bugs.Thanks for the advice......

tombobiche

How to build a UHF antenna...

heres some more stuff from 1963 on the micro horn, later I can put up some on the Rhombic although that all seems horribly impractical for rotation purposes. But the hot rod CM4221 rocks and it should fly pretty good; still working on the grill..

tombobiche

How to build a UHF antenna...

Quote:
Originally Posted by tombobiche
thats awesome thanks mcclap for the shortcut. frankly I was leary of double stacking the 9.5" Ive built not only from weight but lack of funds to set up the baluns. So I'll try setting a reflector on the 4 bay, and keep one in the air, and the other behind the TV.
Its no problem switching the lines between electrical storms, I saw at Lowe's they have the cage wire for $19.95 which is pricey for overall; but a good investment for long term viewing. I bought 25 feet of RG6 and a good external balun at Lowes with a U-Crimp it included, which should be useful for arranging the setup. I agree fully that low loss in digital is vital to maintaining the signal.
They have a little booster at Lowes for $20. I think its one of those 25db boosters for split or extremely long lines so I steered clear of it; I just dont know if its the proper pre-amp, but thats pretty cheap for a 25 db signal amplifier on UHF. For now Ill stay with the mechanical approach; low loss with RG6 and new balun and screen on the 4 bay and the Tepee pole for now. I caulked and painted the base to the external one so any day I can screw in the bowties and work out the reflector bugs.Thanks for the advice......

If you're only running 25ft. of rg6 coax without a splitter or anything an amp wouldn't do much for you. Stay away from those cheap amps a Lowes.
They used to sell the channel master 3041 dsb there, that's not a bad little pre amp but that's about it.

I've now tested 15" 4 bay reflector spacing and it does work, it slightly improves VHF-Hi reception and doesn't degrade UHF much if any. It narrows the band width alittle but and by moving the reflector in or out the gain can be brought back at one edge or the other if needed (14" works better for the upper UHF channels and 16" works better on the lower UHF channels).

I wouldn't mess with it though unless someone needs just a little bit more to receive a VHF-HI station that's on the edge and even then it may not help some channels depending on the size of the elements they are using on thier 4 bay.

mclapp

How to build a UHF antenna...

Hi all,

Here is a pic. of my most current build along w/ a pic from TVFool.com showing my channels.


Here is a list of all the channels I'm getting w/ my Sony KD-34XBR970 HDTV and my JVC DTV.

My HDTV and DTV are receiving OTA signals via my home made outdoor antenna, mounted 30' up on an old antenna mast. My cable lenghts are 50' and 75'(no signal amps). The signal streanth is holding at about 98 of 100 w/ zero dropouts, even during the latest storms. I'm receiving a lot of channels;
2.1 2.2(WDTN),
5.1 5.2(WLWT),
7.1 7.2(WHIO) & 41.1 41.2(WHIO),
9.1 9.2 - 10.3 10.4(WCPO),
12.1(WKRC) 12.2(CinCW),
14.2-14.6(CinPBS),
16.2-16.6(DayPBS) & 48.1 48.2 58.3 58.4 58.5 58.6 58.7(DayPBS),
19.1(WXIX), 22.1(WKEF),
26.1(WBDT),
33.3(?),
43.1-43.5(WKIO),
45.1 45.2(WRGT),
64.1(WSTR)
= 38 digital channels.

hyghwayman
P.S. Click on the attachment to see a better pic of my antenna.

hyghwayman

How to build a UHF antenna...

I trust you used non-conductive paint ...

A similar (9") antenna with reflector in my attic does the same with that TV down to -77.5 dBm, so this result from a bi-directional mounted high outdoors is no surprise.

I would be curious what you see from the CECBs available today. My results are that the new "6th gen" tuners are seriously inferior to whatever tuning/decoding system Sony put in this box.

fbov

How to build a UHF antenna...

Quote:
Originally Posted by fbov
I trust you used non-conductive paint ...
Not sure , I better check!


Quote:
I would be curious what you see from the CECBs available today. My results are that the new "6th gen" tuners are seriously inferior to whatever tuning/decoding system Sony put in this box.
? CECB's, what is that?

hyghwayman

hyghwayman

How to build a UHF antenna...

Quote:
Originally Posted by hyghwayman
CECB's, what is that?
http://en.wikipedia.org/wiki/Comparison_of_CECB_units

dbsc

How to build a UHF antenna...

all my stations are fine and actually the VHF have never been bad, now I'm confident on stations like 3.3, 6, 7 and others always. My main two stations were Fox 33 and KLTS PBS 25. These have always been fringe for me here and I could get them through and about. I like all the PBS junk well enough, and Fox 33 is the only one in my area that plays late nite movies and usually I'm a night owl for that sort of thing.
So grasping for those drove me to rebuild the (your) mcclap 9.5"; it can be maintenanced, I had some trouble figuring out the galvinized spars which screw in; looks like it will be 5.12" back. I had to build the mesh myself from garden junk I found on the highway, and I painted the rustable sections in red, and Im 100% sure Ill get the foward 1.85" sweep to the elements, and using the 36X40 screen it will be molded onto the spars to the specified angle; so all that stuff will be grabbed into the system; thats a good design and I could never have figured out the dimensions; so we'll see if 33 is the highest it can pull since thats low as UHF goes all the way to 82.

I'm sure 2 to 6 db will make or break fox 33 for me, and weatherproofing is consistent with caulking, painting and using weatherproof junk. Total cost so far $6.50 for the RG6 and $4.50 for the external balun.

tombobiche

How to build a UHF antenna...

Quote:
Originally Posted by Falcon_77
In response to my concerns with elements poking out awkwardly on my Hoverman and being a hazard, I built a new one with the final set bend in instead. I was hoping to not take too large of a performance hit, but it is quite substantial. If someone can let me know why the attached doesn't work, that would help me figure out what I can try to change.

If the end elements need to be sticking out, what can I put on the ends to prevent injury?

Also, I discovered that putting a 20dB attenuator on the attic antennas before my pre-amp helped separate the pretenders from the performers. With the signals as strong as they seem to be here, w/o the attenuator it is hard to find much difference between builds.

With the attenuator, the old Hoverman build outperformed my 4-bay-10 build by a significant margin.
Autofils, the GH modeler, has posted that the end stubs are quite important to the UHF Hoverman performance. (The original 1958 patent seemed to imply they were for VHF, but that turned out not to be the case) Adding more diamonds to the design also doesnt help.

So no surprise your performance hit was quite substantial. Go back to the original design and use a 85mm to 95mm feed-gap spacing (versus 44mm shown) for even more performance. For safety issues, you could slip some aquarium tubing over the ends, leaving a lot extra for some droop of the tubing. Or you could use some cheap stryrofoam balls. The same could also be used for the bow-ties, except you would need many more.

@tombobiche
Heh, I certainly wouldnt even consider making any lightning arrestor using wood. Its more of an igniter than an arrestor IMO.

Heres a picture of the DBGH I built. It performs very well.


300ohm

How to build a UHF antenna...

Quote:
Originally Posted by 300ohm
Heres a picture of the DBGH I built. It performs very well.
Do you have a less shadowed picture? Also what did you use to make it?

dbsc

How to build a UHF antenna...

Quote:
Originally Posted by tombobiche
heres an outside view front and back, it does so well I'll probably put it in the attic with a short line through a vent.


http://i180.photobucket.com/albums/x...iveX/front.jpg

http://i180.photobucket.com/albums/x...hiveX/back.jpg
Nice job building it with all recycled materials. How much signal difference did you see with the reflector added?

mclapp

How to build a UHF antenna...

Quote:
Originally Posted by Falcon_77
I don't have any significant UHF ghosts. It is more of a problem for VHF reception (on separates). I thought I would have problems when I first installed the 4228, which was looking through it for about a year before I turned it to KVCR recently. Maybe it is small enough not to cause any problems.
Well, it sounds like you wont know until February if those multipaths will cause you problems. Thats actually the good thing about being able to test reception now.

Quote:
Wind load resistance is important to me, hence individual reflectors rather than screen. (Ill see how it does in a severe thunderstorm predicted for this afternoon, heh)
Eh, it was a maybe 40mph storm. The weather precidictions are generally consistantly wrong. Brace for hell, nothing, brace for a mild storm, and all hell breaks out. My antenna barely moved in the wind.

300ohm

How to build a UHF antenna...

@ tombobiche

I would seriously consider flattening the reflector (using a mallet on a flat board) and straightening (using flat pliers). You may be able to get another db in gain. I have found a few millimeters off can make a difference.

300ohm

How to build a UHF antenna...

Quote:
Originally Posted by 300ohm
@ tombobiche

I would seriously consider flattening the reflector (using a mallet on a flat board) and straightening (using flat pliers). You may be able to get another db in gain. I have found a few millimeters off can make a difference.
The outside edges are supposed to be angled forward to maintain the spacing with the forward angled bowties.

mclapp

How to build a UHF antenna...







Heres some better pics to show that I'm hoping I got the reflector as strait as possible. It was as predicted and indeed this antenna or I'm guessing any bowtie type never comes into it's own without a reflector.
I had the core,( the identical 9.5" without the reflector) on the tabletop watching Fox33 again (Jean-Claude Van Damme movie) and it was pulling 19% sometimes down to 17%); this is my default testing station because its very fringe for me and requires a strong antenna to get it fully. I disconnected that one and put in the one with the reflector on the desktop, and sure enough the signal went up to %73. This is all on the table top on a very faint signal that comes and goes. It maintained that strength throughout or down to %62. So it is a day for night situation and I think this antenna without a reflector is not complete. So I guess its a matter to consider how much a reflector can do on virtually any system; but the 36X40" reflector made the entire antenna about 3.5X stronger.

I'm still very sad I cannibalized my Grey Hoverman for the elements, and looking at the patent I still wish I had it for testing purposes and may rebuild it; however this antenna is the best thing I have ever seen. Even on analogue PBS 24 which is a hard station to get clearly, this antenna with the reflector made it a pleasant viewing experience in analogue; and of course with the increase bandwidth design and predilection it outstrips everything in the digital move to come. On the tepee pole it did grab 5 new stations 12, 12.3 ,21 etc so it has bandwidth strength.
I only have some chicken wire and am thinking about a 6 rod cage covered with 2X2 construction insulation mesh (chickenwire), for the other antenna, for sure I'd be curious to know what your 8 bay with reflector on the rotator pulls compared a 4 bay with reflector.
I did this one as you'd stated; bent 1" from the end of the bowtie and 5" back. This mesh is exteremely light weight and springs too as the galvinized spars retain the position, of cousre the next logical step is solder, flattening of the element joins and aluminum solder to get it ultra light and strong as youve already done, but in wood and the scrap yard theres options too, I was looking at some hard rubber I had and some flat construction steel for the vertical.
Well I'll post some stuff on an FM antenna Im looking at; enjoying Garrison Keeler in the Prarie Home Campanion on NPR.

tombobiche

How to build a UHF antenna...

Quote:
The outside edges are supposed to be angled forward to maintain the spacing with the forward angled bowties.
Heh, what I originally meant was flattening and straightening the wires in the grid. I should have been clearer.

It looks better now.

300ohm

How to build a UHF antenna...

lol I read here the completed array can recieve a coat of aluminum paint, except that the driven element junction should be left uncovered since metallic paint across these connections could amount to an r.f short circuit. But its a good ideaa to apply a final weatherproofing layer of plastic spray to the assembly including all the elements; and to use vice- grip pliers clamped to the bottom of the pole for rotation.



tombobiche

How to build a UHF antenna...

Quote:
Originally Posted by tombobiche
lol I read here the completed array can recieve a coat of aluminum paint, except that the driven element junction should be left uncovered since metallic paint across these connections could amount to an r.f short circuit. But its a good ideaa to apply a final weatherproofing layer of plastic spray to the assembly including all the elements; and to use vice- grip pliers clamped to the bottom of the pole for rotation.
I hadn't considered a polyurethane type spray for weatherproofing. What a great idea!

I wouldn't mind weatherproofing my 9.5" 4-bay, and mounting it outside just over the peak of the garage roof...
Maybe I'll mask off the elements, and paint the 2x4 as well!

strudel.chris

How to build a UHF antenna...

Quote:
Maybe I'll mask off the elements, and paint the 2x4 as well!
Masking is a pain. I would think removing the elements, then paint, then replacing the elements would be easier and neater.

300ohm

How to build a UHF antenna...

As 300 ohm said, if your using wood I'd suggest painting it first before installing the elements or phase line.

Stay away from silver paint, or any other metallic paint as it may contain some metal particles in it. Since all the elements are driven elements in a 4 bay you'll short out the whole thing.

White is a good choice, clear coat would be good too. After you have the antenna assembled an overall coat of non-metallic paint would be fine.

By the way 300ohm your double hoverman looks really nice and I'm sure it performs as well.

tombobiche the 8 bay I have up only very slightly out-performs the 4 bay when mounted in the same place. It's an experiment using a different feed system I'm going to take it down soon to try something different but I'm concentrating on the 4 bay right now. As you saw that reflector makes a huge difference in the 4 bay.

Any one who has built one of these 4 bays using the dimensions I posted let me know how it's working, post some pictures. The more I can learn from people using these the better chance I have in tweaking the design for best results.

Has any one tried the 15" reflector spacing for enhanced VHF-HI reception?

I tried it on my wooden test mule and it worked well, a noticable improvement on some VHF-hi stations and no noteable change in UHF.

mclapp

How to build a UHF antenna...

mclapp and others who have given advice i finally got my four bay put together....
now to figure out the reflector.. By the way im doing a single hoverman too...ahh
work in progress.. let you know how it all works in the next few days.


John

EDIT

OK i took it outside no reflector on the four bay its pulling two scranton stations vhf wbre and wyou lol wskg wbng wicz out of Binghamton now i need to go and get some reflector material.
these are all below threshold about twenty five thirty percent..

By the way i ordeded a vhf high band yagi from solid signal see
how that puppy does it was a five element antenna craft cheapie
I cant wait to toss the cable


JOHn

johnied

How to build a UHF antenna...







I retested the reflector using these horizontal bars and 2X2" chicken wire behind it as a quick and easy reflector. It works really good and was up late night on Fox 33 watching a Catherine Deneuve movie. I tried bending it like the channel master and got no better results than flat. But my advice is if you can get the 1X2" mesh in light aluminum or stainless then use it as mcclap's dimensions in 36X40", that makes for more dbs.
I figured out how to rig the mast. I'll drill two holes through the reflector supports and then screw the steel pipe into the back of the upright wooden support; that will make it very strong, then since the pipe is about 12 feet long, bolt two pipes together in the middle side by side. Then it can be dropped into a swivel or simply buried in the ground, and any top support can be adjoined to a stucture or fence. Then it can be rotated with pressure pliers for remembering stations.
Heres a Rhomic with lengths no more then 55". Ive never tried this and doubt it can beat our bowtie/Hoverman endeavors but maybe it could work. Rhombic goes the size of the yard without rotations. Ive seen tabletop mini rhombic amplified systems.

tombobiche

How to build a UHF antenna...

Quote:
Heres a Rhomic with lengths no more then 55". Ive never tried this and doubt it can beat our bowtie/Hoverman endeavors but maybe it could work. Rhombic goes the size of the yard without rotations. Ive seen tabletop mini rhombic amplified systems.
Well, that one is only about 4 - 5 wavelengths per leg long. IIRC, rhombics generally only get good with around 10X wavelengths per leg long. But I also recall seeing rhombics like that stacked 3 high that claimed something like 25db gain. (Seeing in an article design drawing, not in real life) They can get to be monsters.

Building something like that could be done with hard copper 3/8 ID inch (what that plan calls for) or 1/2 ID inch copper pipe, but it would get very expensive now, if youre buying new hard copper pipe. It could also maybe be made using 1/2 inch pvc pipe, and then stretch the wires inside of that form.

300ohm

How to build a UHF antenna...

Quote:
Originally Posted by 300ohm
IIRC, rhombics generally only get good with around 10X wavelengths per leg long. But I also recall seeing rhombics like that stacked 3 high that claimed something like 25db gain
Now THAT I would love to see (not that is practical, or anything

mattdp

How to build a UHF antenna...

Quote:
Originally Posted by johnied
mclapp and others who have given advice i finally got my four bay put together....
now to figure out the reflector.. By the way im doing a single hoverman too...ahh
work in progress.. let you know how it all works in the next few days.


John

EDIT

OK i took it outside no reflector on the four bay its pulling two scranton stations vhf wbre and wyou lol wskg wbng wicz out of Binghamton now i need to go and get some reflector material.
these are all below threshold about twenty five thirty percent..

By the way i ordeded a vhf high band yagi from solid signal see
how that puppy does it was a five element antenna craft cheapie
I cant wait to toss the cable


JOHn
Well now you know the signals are there which is how all this started right.

A reflector on that 4 bay will be a big improvement.

How high did you have it?

If you get the 4 bay finished with the large reflector it would be interesting to see how it stacks up to the high band yagi.

I'm positive it will be some amount less but how much less would be interesting to know.

If you want to make a quick and easy reflector that will work almost as good as screen I have something for you to try.

What you'll need is something to make a frame 36" x 36" and about 65ft. of wire. The wire can be anything steel, aluminum, copper and any gage coated or uncoated.

(1) Make a frame out of wood or metal so that you end up with 2 vertical uprights 36" high and 36" apart.
If the frame is made of metal using bare wire would be best so that the frame can also be an integral part of the reflector.

(2) Drill holes the size of the wire you have 2" apart the entire length of the vertical frame members

(3) Start at the very top and string wire back and forth between the frame members all the way to the very bottom so that you end up with wires running parallel 2" apart horizontally. It's ok to splice multiple pieces of wire together just try not to do it on a horizontal section.

Center the grid 14" behind the phase lines of the driven elements.

This is not as good as the angled wire mesh reflector but it's pretty close about 1-2 db less on UHF, and could be much cheaper especially if someone had some scrap wire kicking around.

Someone could make an angled version with some extra frameing.

Have Fun

mclapp

How to build a UHF antenna...

Here a link to the web page:

http://www.tvtechnology.com/features...5-f_doug.shtml

"On p. 35, there is a description of DHR (dual hexamerous rhombic) antenna designed for the 430 MHz band. It should work well at UHF frequencies. The calculated gain of the 2x6 rhomboid antenna is 33 dB! "

Heh, what a monster. Good luck finding a rotor for it.

300ohm

How to build a UHF antenna...

Quote:
Originally Posted by [B
fbov[/b]
I trust you used non-conductive paint ...

Not sure , I better check!

hyghwayman
Ok after checking I found it was indeed metalic crome paint.

Thanks for asking!
hyghwayman

hyghwayman

How to build a UHF antenna...

One never knows when the odd thought passing through one's mind might be an "oh sh*t" passing through someone else's ...

And I'd like to add a brief word of thanks to those who read and contribute to this thread. I found it dormant 3 months ago when I first posted on page 1. This is page 10 ... lots more good stuff here than I ever would have dreamed!
Thanks,
Frank

fbov

How to build a UHF antenna...

I built an LPDA two weekends ago following these plans: http://www.qsl.net/va3rr/hdtv/HDTV.htm

The guy has done some modelling of the design and it seems reasonably effective (for the size) though not terribly impressive. I had better results spacing the two booms apart about 3/4", maybe a little less. I'm not sure what the resulting impedance is but it's working better.

Comparing to an off-the-shelf, unamplified Silver Sensor, it beats it in one location in my house where it actually brings in a channel I couldn't get before (something like 8kW on channel 57 some 20 mi. away) but is worse or comparable in other areas of the house.

I added a air-choke and a ferrite choke similar to this: http://www.vk2zay.net/article.php/43

Out of curiosity I took apart the SS and found its internal design to be very similar, though it doesn't have any sort of choke or transformer inside.

cpldc

How to build a UHF antenna...

Heres one I found log periodic I tried this one not in PVC but in wood and didnt get too good results with it. It could always be the construction though. And heres a Yagi I tried that didnt work either, I used the rods from on old VHF antenna, may have been off a bit in dimensions.
But Im very glad to get the VHF this way, was watching tennis on Channel 6 with it and dont plan to go aereal until the news about Lousianna Public Broadcasting is know where theyll build a tower for Channel 25 KLTS at only 48KW radiating power,but so far everything is acceptable from the table top.

P.s the Log periodic is from mother earth news May/June 1985

tombobiche

How to build a UHF antenna...

Quote:
Heres one I found log periodic I tried this one not in PVC but in wood and didnt get too good results with it.
Yep, I built that one in wood too, and pretty much all the Popular Electronics antennas published up to 1987. (MotherEarthNews plagerized that one from them, the Pop Elect one was about 1979-1981 IIRC.) It performed pretty mediocre in my attic, but Log Periodics are mostly about bandwidth and not gain. I have an old suburban type vhf/fm/uhf with a 30 inch boom in my collection that basically outperforms it. Its actually a fanscinating simple design, and I dont know who made it in the early 70's. From the measurements it follows all the rules. The uhf part of course is weak, but from 60 miles out, I get pretty much all vhf, high and low, almost snow free. Not bad for the boom length.

I like the old articles you have posted. Are most of them from old 1950s and 1940s Popular Mechanics ?? Ive some of them too.

@mclapp,
Yeah just like you, Ive found that most of the 8 bay bowties Ive built in the past performed maybe a hair better or a hair worse than the 4 bay versions. But, nowhere near the 2.5 to 3 db gain or something like it should have. I was pleased that I did get a very noticable gain on the DBGH over the single bay SBGH version.
It has to be in the phasing line between the two 4 bays. Have you tried straight phasing lines like on the CM4228 or the "V" straight phasing line like on the AntennaCraft U-8000 ?

300ohm

How to build a UHF antenna...

[quote=300ohm It has to be in the phasing line between the two 4 bays. Have you tried straight phasing lines like on the CM4228 or the "V" straight phasing line like on the AntennaCraft U-8000 ?[/QUOTE]

I use 450 ohm ladder line it seems to work the best with the limited testing I've done.

I tried a feed like the cm4228 but wasn't impressed, that style feed system should work good but something seems to be off with it.

The major problem is that your taking (2) 300 ohm antennas and combining them to a common feed point which cuts the feed point impedance in half, that turns into a mismatch which = loss.

I know that each half of the 8 bay is not 300 ohms at all frequencies but it's pretty close on most.

I've tried a few computer simulations of different feed set-ups but really haven't put much effort into it yet.

I'm concentrating on the 4 bays and when I think I've got all I can out of the 4 bay I'll work on a stacking arrangement either vertical or horizontal.

mclapp

How to build a UHF antenna...

Quote:
tried a feed like the cm4228 but wasn't impressed, that style feed system should work good but something seems to be off with
Before you disassemble, try the AntennaCraft U-8000 "v" straight feed design using just equal straight wires. (Boy, I thought I was weird having open wire 300 ohm stuff, but even Ive never even heard of the 450 ohm ladder stuff, HAM radio I presume).

And just in case anybody is interested, the last 4 and 8 bay bowties I built were in the real bow-tie type design, in other words each section looked like a skinny heart. Copied from a Sony portable Uhf design that came with the set, about 7 inches long and 3 inches high. Didnt perform any better than a "whiskers type" design. At least I can scrap it and make a 8 and 3/4 inch whiskers design from it. Even though in my situation I need channels 6 and 12, Im very curious to see how channel 12 will perform with a 15 inch spacing reflector.

300ohm

How to build a UHF antenna...







Well I guess this is painfully obvious but its possible that working with the baluns then the twinlead maybe better for the equal splice, at least I forgot how to do it. Of course I knew I had good reception but had no way of seeing the dbs it was getting.
But I understand the CM is 8" and 9.5" or 10" works excellent on VHF; and it also does extremely well on anything UHF; in the air it does master the sky.

tombobiche

How to build a UHF antenna...

Quote:
Which would be a better mount?
Higher isnt always better, if going higher means aiming at an obstruction like a tree canopy or a house etc. What you want to look for is a clear space or opening in front of the antenna for quite some distance for best results.

If you cant find an area free of trees, then you may have to make a choice. Thick fir type trees block the signal more than broad leaf type trees. And fir type trees block the signal year round.

I just cut down some branches to create a clear path for my garage antenna. The difference in signal strength is amazing.

300ohm

How to build a UHF antenna...

Quote:
Originally Posted by 300ohm
Black PVC, I assume he means ABS pipe.
Actually the best paint to use for plastics in my experience is the vinyl color paint sold at places like Pep Boys. Its more of a plastic dye than a paint and is much nicer in self leveling, ie harder to make it run. Its ketones, toluene, xylene based and about $6 a can.
I think he did actually mean black PVC but he said a lot of stores don't carry it. Someone on another forum remarked that there was black Schedule 40 PVC , not ABS, in the irrigation/sprinkler section of lowes in his area though some irrigation pipe is ABS. You want a pretty thick coat of the "dye" to catch all the UV. I am not surprised that one based on lots of nasty solvents appears to work best.

Quote:
Yeah, the Florida sun is murder on boats. The gel coat on boats fades at least 3 times as fast in Florida than in Delaware. Brand new boats in Florida look old in only 3 - 6 months if not frequently waxed, heh. I imagine Dhahran is worse. So, for people South Carolina and down, its probably worth the extra trouble and expense to locate the UV resistant type pvc. And the UV stuff also makes sense if keeping the antenna for more than about 8 years or so here. But my gut feeling is that Ill be changing my antenna long before then, heh.
Also Ive noticed that a lot of places use the electrial pvc conduit outdoors.
That may be one reason the conduit tends to be a darker color.

Quote:

"Can PVC pipe be exposed to the sun?
PVC does not readily degrade when exposed to sunlight (ultraviolet radiation) due to natural UV inhibitors present in the material. Short-term exposure to sunlight, such as during construction, is typically not a problem for PVC pipe. PVC piping may be used in outodoor applications when the piping system is painted with a light-colored water based acrylic or latex paint that is chemically compatible with PVC. When painted, the effects of UV exposure are significantly reduced. "

Hmm, light colored. I may have to rethink my color scheme. Flat silver or chrome perhaps ?
Avoid the metalic colored or metalic paints (such as car paint) as they tend to actually have metal in them. I am not sure their advice to use a light colored paint was good advice. A light colored paint might last longer, as it absorbs less UV, but it might not protect the PVC all that well. White PVC doesn't work well outdoors because it is too translucent so the UV can penetrate. Anyone who has ever tried to paint white over a darker color knows white paint suffers from a translucency problem. Red paints also tend to fade very quickly outdoors compared to blue paints because they absorb more UV, though some red paints are made to be more robust. Black tends to absorb the UV as it gets absorbed in the pigment (often carbon black). That means the pigment gets hammered pretty hard but carbon black, unlike the plastic or coating containing it, is already chemically as simple as it is going to get so it may withstand the hammering - it converts the UV into heat instead of chemical damage. Carbon black is pretty safe environmentally, as carbon is a constituent of all known living things on this planet, as long as you don't snort large quantities of it (black lung disease). Black gets cooked thermally pretty hard in the summer but may stay warmer on winter days, which is good, but may be cooler on winter nights, which is bad.

I have specifically seen that carbon black is added to some plastics to harden it for outdoor use. Metal additives (lead, tin, etc) are also used.

whitis

How to build a UHF antenna...

Quote:
Originally Posted by 300ohm
Higher isnt always better, if going higher means aiming at an obstruction like a tree canopy or a house etc. What you want to look for is a clear space or opening in front of the antenna for quite some distance for best results.
Yeah, higher is better except when it isn't. In most cases it is seriously advantageous to go higher (very crude estimate 1dB per foot). However, the highest point on your mast might be a local minimum for signal and a location a few feet lower or sideways might work better. Thus, on average higher is better but you want to find the sweet spot.

Going higher till you get line of sight is best, but isn't necessarily practical. If the signal isn't line of sight, it is probably being diffracted off the tops of trees or houses. And signal strength degrades heavily the larger the angle from the tops of the obstruction to your antenna.

Sometimes you can shoot under an obstruction, such as tree branches, though the signal will probably be pretty weak down there. In some cases, you may also be able to take advantage of a ground bounce though that is likely to be weak and may get obstructed by things like cars. Wherever you are considering, it can help to look for the sweet spot. The sweet spot may move, however, if, for example, the signal is diffracted off tree tops which can move in the wind or as the tree grows.

Lots of unobstructed distance in the direction of the antenna beam only helps if there is actually signal there. Better to shoot through a few leaves or where an obstruction only barely gets in the way (and thus has a low diffraction angle) in a direction where there is signal than to aim in a direction where you can see further but hit an obstruction which is much higher than an imaginary line of sight.

Guidelines are just that. They don't tell you where the strongest signal will actually be, they just give you hints regarding the best places to begin your search for it.

whitis

How to build a UHF antenna...

Quote:
I am not sure their advice to use a light colored paint was good advice. A light colored paint might last longer, as it absorbs less UV, but it might not protect the PVC all that well. White PVC doesn't work well outdoors because it is too translucent so the UV can penetrate. Anyone who has ever tried to paint white over a darker color knows white paint suffers from a translucency problem.
Yeah, I agree. Another example is painting on glass, lighter colors let the light thru. I think they made that recommendation to please homeowners who like to color match.
Ill have to check out that irrigation/sprinkler pipe at Lowes. Of course its meant to be buried.
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(very crude estimate 1dB per foot)
That old rule of thumb doesnt seem to apply to my TVFool report. Going from 35ft to 65ft gives me a .6 to 13.3db range of increase according to them, with most channels falling into the 1 - 2db increase range.
Quote:
I have specifically seen that carbon black is added to some plastics to harden it for outdoor use. Metal additives (lead, tin, etc) are also used.
Yeah, Ive seen some 100 - 150 year old outdoor signs painted lead/tin based paint still in fairly good shape. Of course, its poisonous, but the old formulations are hard to beat.

300ohm

How to build a UHF antenna...

I got my 12" wisker 4 bay up this weekend and it works well for the distant ch18 station I'm trying to receive as compared to the 10" wisker 8 bay I've been using. It has 11 3/4 " element spacing, 4" reflector spacing and the reflector is made of 1" x 2" wire mesh.

I really doesn't seem to have any negitive visual effects on the other channels 7,8 & 42 digital and 12,26,34,40 & 46 analog. I don't have a signal meter that's fine enough to show the difference.

On another subject, I found a piece of electrical conduit made from gray colored PVC that has been exposed to the elements for a minimum of 5 years it appears to be faded some and I'm sure it's degraded some but still seems to be quite sound and flexiable.

Of course I live in the ever cloudy north east so it gets no where near the UV exposure that alot of the country would.

mclapp

How to build a UHF antenna...

Quote:
Originally Posted by 300ohm
Yeah, I agree. Another example is painting on glass, lighter colors let the light thru. I think they made that recommendation to please homeowners who like to color match.
Ill have to check out that irrigation/sprinkler pipe at Lowes. Of course its meant to be buried.
Yeah, though the sprinkler heads themselves are exposed to the sun and the pipe may be exposed to the sun in places like where it attaches to a timer mounted on the wall. And when used to irrigate plants instead of lawns it may be elevated. So there is a chance it is designed for sunlight exposure.

Quote:
That old rule of thumb doesnt seem to apply to my TVFool report. Going from 35ft to 65ft gives me a .6 to 13.3db range of increase according to them, with most channels falling into the 1 - 2db increase range.
At higher elevations I would not expect it to hold. It isn't linear and once you reach line of site, elevation doesn't matter. It is a pretty crude rule of thumb.

Quote:
Yeah, Ive seen some 100 - 150 year old outdoor signs painted lead/tin based paint still in fairly good shape. Of course, its poisonous, but the old formulations are hard to beat.
Really? They haven't been restored? You can find lots of pictures of badly faded old signs much younger than that, mostly painted on brick walls because if the structure depended on the paint to protect it, that protection would have been long gone. (ghost signs).
Also, are you sure they were lead paints? Were they well shaded?

Interestingly, lead paint has been known to be a serious health risk since 1897 (lead toxicity has been known for 3000 years) and was banned in 3 countries in 1909 and by 1934, it had been banned in at least 11 countries. In 1938, the lead industry ran a campaign showing babies and children touching paint and promoting lead paint for children's cribs, toys, and furniture. Paint is a particularly dangerous application of lead, where children are concerned.

However, banning lead in electronics is a dubious proposition. The environmental impact of lead-free solders is considerable and is multiplied due to the shorter expected lifetime.

whitis

How to build a UHF antenna...

Quote:
Yeah, though the sprinkler heads themselves are exposed to the sun and the pipe may be exposed to the sun in places like where it attaches to a timer mounted on the wall. And when used to irrigate plants instead of lawns it may be elevated. So there is a chance it is designed for sunlight exposure.
Yeah, I went to my local Lowes today and saw that 1/2 inch sch 80 pvc lawn sprinkler riser stuff. Its plainly labeled for "outdoor use only". The only trouble is its $3.57 for 4 feet, one reason its expensive, its threaded.
They also had grey sch 80 10ft pieces 3/4 inch - 1 1/2 inch for lower prices, but no 1/2 inch.

I also looked closely at the grey electrical conduit sch 40 they had. On the pipe it said "rated for below and above ground use". So that would imply outdoor longevity. Since its only $1.09 per 10 ft versus $1.69 for sch 40 water grade pipe, I would recommend its use for a couple of reasons.
The only trouble is, no grey outdoor ells, tees etc. But regular pvc fittings work on those fine.
Quote:
At higher elevations I would not expect it to hold. It isn't linear and once you reach line of site, elevation doesn't matter. It is a pretty crude rule of thumb.
Yeah the ones Im comparing are LOS, and TVFool doesnt realize I have the tallest tree for miles around. Once I get my antenna on it over the top of all the trees, I should expect at least another 3 db gain (doubling) in signal power, heh.

Quote:
Really? They haven't been restored? You can find lots of pictures of badly faded old signs much younger than that, mostly painted on brick walls because if the structure depended on the paint to protect it, that protection would have been long gone. (ghost signs).
Also, are you sure they were lead paints? Were they well shaded?
Yep, and now that you mention it, I remember seeing completely UNRESTORED signs (1700's Ladies boots ads , heh) and outdoor church frescos in very decent shape after 250 -300 years in an eastern european country I visited in 1991. Shady place ? I would say medium shade. On the other hand, they were covered over by cheap Soviet whitewash paint for about 50 years, that stuff would rub off on your clothes, and eventually it just plain wore off of the above signs, heh.

300ohm

How to build a UHF antenna...

Here's some info on antenna height.

http://www.ham-radio.com/k6sti/height.htm

Ron

dr1394

How to build a UHF antenna...

Quote:
Originally Posted by 300ohm
I also looked closely at the grey electrical conduit sch 40 they had. On the pipe it said "rated for below and above ground use". So that would imply outdoor longevity. Since its only $1.09 per 10 ft versus $1.69 for sch 40 water grade pipe, I would recommend its use for a couple of reasons.
The only trouble is, no grey outdoor ells, tees etc. But regular pvc fittings work on those fine.
Electrical PVC also can have 'sunlight resistant' for long term exposure to UV from sun.

In the electrical you can find 90 degree curves or pulling ells or tees. Though they aren't the best shapes or strength for making structures, plus costly.

Yes the plumbing fittings do fit and give the tight 90 or tees, though should paint for UV exposure.

johnpost

How to build a UHF antenna...

i have a bundle of 0.032" MS20995C32E spec wire. can i use it to make the antenna?

Skylinestar

How to build a UHF antenna...

Quote:
Originally Posted by Skylinestar
i have a bundle of 0.032" MS20995C32E spec wire. can i use it to make the antenna?
That sounds like it is probably stainless steel aircraft safety wire. There are some problems. 0.032 is pretty thin and might not be rigid enough for the elements. Though stainless can be pretty stiff compared to other materials, safety wire isn't intended to be that stiff. Also, with thinner wire you need to make the phasing line spacing thinner and at the spacing that would likely result, it would be difficult to keep the wire from shorting let alone maintain consistent spacing. And these changes will deviate from modelled results.

That wire would probably be better suited for a rhombic antenna, if you have the space. My guess is a rhombus around 80" on a side with interior angles of 135 and 45 degrees would probably work pretty well at UHF (17.38dBi raw gain) except for having an impedance of about 900 ohms. 12:1 baluns are hard to come by and with a 4:1 balun you lose around 4.77dB However, the VSWR would be very flat 3:1 over the whole band and other antennas may lose that much raw gain at the edges anyway. Thus your worst case performance would be better than the best commercial antennas but your peak performance near the center of the band would be lower. You could run a tapered transmission line from the back (0.5625" wide with 0.03125" wire diameter) to the middle (0.1875" spacing) but you would need to tension the wire and maybe use some spacers made from something like PVC siding to maintain the spacing to give an almost perfect VSWR match. A triple wire rhombic would be expected to give about 18.74dBi at 600 ohms with a VSWR of 2:1 or a raw gain of about 15.74dBi +/- 0.5dB across the whole VHF band. But not everyone has room for a 12' x 5.5' foot antenna. None of this has been modeled - it is just estimates from scaling another design.

When size isn't an issue, pretty much nothing beats a rhombic for broadband performance. Except maybe a parabolic dish (feedhorn could be an issue,though).

whitis

How to build a UHF antenna...

Quote:
Yes the plumbing fittings do fit and give the tight 90 or tees, though should paint for UV exposure.
I cant believe I didnt think of it before, but automotive and marine paints are highly UV resistant. The paint used on plastic bumpers should be fine for pvc. Just have to check on the can what base is used, and make sure it doesnt contain metallic particles.

Edit: I bought a couple of 10ft lengths of the grey 1/2 inch pvc electrical conduit today, and it does say on the pipe "sunlight resistant". Yay ! It does does seem to be just a hair "floppier" than the water grade stuff though. Probably a little softer.

300ohm

How to build a UHF antenna...

Quote:
Originally Posted by 300ohm
I cant believe I didnt think of it before, but automotive and marine paints are highly UV resistant. The paint used on plastic bumpers should be fine for pvc. Just have to check on the can what base is used, and make sure it doesnt contain metallic particles.
Unless you get that stuff that GM used a few years ago, the sun went right through it and made the primer chalk up then the paint came peeling off.

Quote:
Edit: I bought a couple of 10ft lengths of the grey 1/2 inch pvc electrical conduit today, and it does say on the pipe "sunlight resistant". Yay ! It does does seem to be just a hair "floppier" than the water grade stuff though. Probably a little softer.
I've also seen PVC fittings in light gray and dark gray but it didn't say any thing about the UV resistance or for outside use. They were also pretty expensive compared to the white ones about 3x more.

mclapp

How to build a UHF antenna...

Quote:
Unless you get that stuff that GM used a few years ago, the sun went right through it and made the primer chalk up then the paint came peeling off.
Yeah. The black paint Mitshubishi used in 1991 did about the same thing to the roof and hood. So I guess the lesson to be learned here is to look at cars about 15 years old in the color you want to use, and judge its durability from that, heh.

Quote:
I've also seen PVC fittings in light gray and dark gray but it didn't say any thing about the UV resistance or for outside use. They were also pretty expensive compared to the white ones about 3x more.
Regular tight angle tees and ells ? Heres a picture of the stuff I got today. Its only $1.09 per 10ft section versus $1.69 for the water grade stuff at Lowes.



On another note, my Lowes has 3/4" to 1 1/4" snap on by thread tees similiar to my homemade tees, but theirs seems to have an even better grip. Ill have to make adjustments to my cuts to make them even tighter.

300ohm

How to build a UHF antenna...

Quote:
Originally Posted by 300ohm
I cant believe I didnt think of it before, but automotive and marine paints are highly UV resistant. The paint used on plastic bumpers should be fine for pvc. Just have to check on the can what base is used, and make sure it doesnt contain metallic particles.
The catch with auto paint is that they pretty much are all "metalic" paints containing metallic particles. An exception might be paints used for industrial vehicles (like the old mail jeeps). Railroad car paint doesn't seem to have that metallic look. The label on the can probably won't tell you what you need to know, but the MSDS might.

whitis

How to build a UHF antenna...

One catch with outdoor PVC is that the additives used to make them UV resistant are usually metalic.

It isn't clear exactly what effect metallic additives in paint and plastics will have. If the metal is high enough density to make it conductive than it will act a bit like a metal pipe, though if it is poorly conductive it may act more like the next category. If the paint is somewhat resistive, then it will act as a signal absorber. If, in the mostly likely case, the plastic is highly insulating, then the metal particles are capacitively coupled to each other through a lossy dielectric and that is harder to figure out.

whitis

How to build a UHF antenna...

Quote:
Originally Posted by 300ohm
I cant believe I didnt think of it before, but automotive and marine paints are highly UV resistant. The paint used on plastic bumpers should be fine for pvc. Just have to check on the can what base is used, and make sure it doesnt contain metallic particles.

Edit: I bought a couple of 10ft lengths of the grey 1/2 inch pvc electrical conduit today, and it does say on the pipe "sunlight resistant". Yay ! It does does seem to be just a hair "floppier" than the water grade stuff though. Probably a little softer.
plumbing pvc is stiffer and more brittle, you don't want sags and dips in plumbing.

check different brands of electrical pvc, some are floppier than others. the stiffer stuff is better for structural uses.

johnpost

How to build a UHF antenna...

Quote:
Originally Posted by whitis
The catch with auto paint is that they pretty much are all "metalic" paints containing metallic particles. An exception might be paints used for industrial vehicles (like the old mail jeeps). Railroad car paint doesn't seem to have that metallic look. The label on the can probably won't tell you what you need to know, but the MSDS might.
Yeah. Im starting to think the Plasti-Kote Vinyl Color paint/dye that Ive always used on plastics is the best, and its completely non conductive.
On the can it reads "For use on the following vinyl items: furniture, panel covering, footwear, luggage, sporting goods, hand bags, auto tops, upholstery, dashboards, visors, boat decking, cushions, chair pads, bicycle seats and many other vinyl items." So pretty high UV resistance is needed for those applications. Its only problem is at $6 a can its pricey.

Quote:
One catch with outdoor PVC is that the additives used to make them UV resistant are usually metalic.
Well, I just measured the grey sch 40 pvc stuff with my VOMs. Its reading a higher resistance than any meter I have can register, (100s megohm range), even when I pierce into it. So if theres any conductive metal in it, its in the atomic proportion amounts.

300ohm

How to build a UHF antenna...

Not a good test. Paints with suspended metallic particles will not necessarily be conductive, but they will still cause problems.

nybbler

How to build a UHF antenna...

Quote:
Originally Posted by nybbler
Not a good test. Paints with suspended metallic particles will not necessarily be conductive, but they will still cause problems.
Hmm, OK another test. I put a super magnet (from an old hard drive) on a small piece of that pipe and its not affected. So no significant amounts of iron. In a way, it makes sense that electrical conduit would be ideally shielded, but at $1.09 retail for a 10ft length, theyre not going to be putting in the pricier metals. At that price, its lucky if there is flame retardant in it, heh.

If you mean the paint, same thing, no measureable resistance and not magnetic. I painted my keyboard with it. After 3 years, its still holding tight from daily abuse.

300ohm

How to build a UHF antenna...

Well, I tried to correlate signal strength with error rates, using a WINTV-HVR-850 on linux with azap and about 7 hours of data. Data was taken on channel 41 (WHTJ-HD, Physical channel 46, 665 Mhz) during good weather.

There are some problems. When I did a scatter graph of signal strength vs. SNR, I got a peculiar plot where many of the points lined up perfectly (too perfectly) on a line and the rest were in a random cloud. Changing the plot to draw lines, the random points appeared to connect to points on the line before and after rather than other random points which indicates that there is a problem with the measurements not being taken simultaneously in time. I suspect the signal strength number is just the snr number rescaled and isn't based on the actual signal strength or gain at all. Bit error rate is reported but is always zero so the hardware probably isn't measuring BER. Uncorrected errors are reported and seem to be real. The signal strength/snr are in random undocumented units (unsigned 16 bit integer). It isn't even known if it is linear or logarithmic. Based on some discussion of similar hardware, it is possible that for SNR minimum scale corresponds to -10dB and max scale corresponds to 40dB. The original 7 hours of data, taken overnight, had no errors but I took another half hour (36 minutes?) of data today when I was getting visable errors.

So, the results are qualitative rather than quantitative but they are interesting in that they show very brief and extreme loses of signal on a background of steady but highly fluctuating signal.

signal2.pdf

I did another test where I turned the amplifier on and off repeatedly.

signal3.pdf

You can see some errors where I pushed the button (push on/push off) but very little indication on the signal or SNR plots. The difference between amplifier on and off is very subtle and is hard to see against the background variation.

Note that there is normally a blip about 2 seconds after initial signal acquisition that is probably the result of training the echo cancellation and there is a glitch at zero which is the result of non-data lines at the beginning of the file.

This data suggests that receiver/amp noise had a barely measurable effect, the tuner AGC was not at full gain, and that it is the presence of ambient noise rather than the absence of signal that was responsible for dropouts. It also suggests that the dropouts were so severe that gain would not help unless it was directionality that excluded the noise source.
Past experience, however, showed weeks of undisturbed signal reception before a cockatiel re-aimed my antenna (Silver Sensor).

I didn't upload the 7 hour plot, during which no errors occured after a few seconds. It looked similar, qualitatively, to the right hand side (1600+) of signal2.pdf. Very flat over the long term (hours) with a lot of fluctuation in the short term (seconds). Since sampling was at 1 second, the frequency of the fluctuations was probably less than one second - i.e. frame to frame or subframe intervals.

I was watching TV using a Zenith DTT-901 CECB during the interval of the half hour measurement (signal2.pdf) in a different room. The experience was similar to what the plot suggests suggesting the two receivers did about as well. Brief dropouts with about the same frequency of occurrence. The WINTV-HVR-850 connects directly to the channel master 0772 amplified video control center (switchbox with amp) while the CECB goes through a VCR and a DVD recorder plus its own internal non-active passthru splitter. Thus the passthru effects were not significant, but this is not surprising with the CM-0772 amplifier.

In general, receivers need better quality metrics, more useful displays of those metrics and gain calibration. It wouldn't be that hard to do for mass production. A single ATSC synthesizer (A PC with a high speed DAC driving an upconverter or ATSC baseband to RF modulator) that is transmitting signal amplitude information, adjusted for constant splitter loss, embedded in PSIP could drive hundreds of receivers during burn in or pass/fail testing and the receivers could self-calibrate and store the results in eeprom. At the same time, the various FCC ensembles could be tested and the receiver could display pass/fail results using the on screen display. By making the JTAG port accessable through a hole in the case, the detailed results could be retrieved for statistical process control (or retrieved directly via USB, etc. for computer tuners). For CECBs and other set top boxes, the results could be transmitted during the vertical blanking interval. Results could also be transmitted, IR remote style, over one of the status LEDs. There is a modest one time cost per factory, a trivial per model cost for integrating the software library, and a negligible per unit cost to perform the testing since you have to power it on and connect an antenna to perform pass/fail testing anyway. Thus, transistor gain variations is no excuse for displaying signal strength in non-calibrated units. In addition, the software library could display signal vs time and signal vs. frequency and simultaneously display signal strength in dBm, signal to noise in dB, bit error rate, and uncorrected error rate. Ultimately, this not only provides a better product and increases sales and goodwill but can lower product return and tech support costs so the actual cost may be negative. 120 testing stations
at $200 each ($24000) with a 2 minute test time let you crank out 3600 units per hour (86,400 in 24 hours, 3.3 million per year) and costs just $0.25 each amortized over the first days production or $0.00073 per unit amortized over the first years production. Labor to plug and unplug cables is 2 cents per unit, and you need to do that anyway and since the test station automatically initiates the test mode and evaluates the results, that doesn't need to be done by people so labor results may actually be lower.

whitis

How to build a UHF antenna...

Quote:
Originally Posted by 300ohm
Hmm, OK another test. I put a super magnet (from an old hard drive) on a small piece of it and its not affected.
That was even less meaningful than the first test. You can put a lot of metal in a plastic without it showing up on a magnet or multimeter. If 10% of the plastic, by weight, was powdered aluminum each aluminum particle can be encapsulated by plastic (thus passing the resistance test) and there is no noticable effect when a permanent magnet (or even an 60hz AC magnetic field) is applied. Now, if you applied a VERY powerful high frequency AC magnetic field, the plastic might get noticeably hot.

whitis

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