How to build an indoor VHF antenna - AVS Forum
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post #1 of 57 Old 04-30-2008, 01:49 PM - Thread Starter
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What is the best material to use to build an antenna? Copper? Aluminum? Steel?

Is it a good idea to put something behind the antenna to reflect signals towards the antenna? Like a sheet of shinny aluminum foil?

What is the best shape and legnth to get CBS HDTV in Chicago (2.1) from about 25 miles away?

I've gotten sick buying every antenna in the store and nothing works. I'm ready to try and build something myself.
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post #2 of 57 Old 04-30-2008, 06:26 PM
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Quote:
Originally Posted by doogiehowser View Post

What is the best material to use to build an antenna? Copper? Aluminum? Steel?

Is it a good idea to put something behind the antenna to reflect signals towards the antenna? Like a sheet of shinny aluminum foil?

What is the best shape and legnth to get CBS HDTV in Chicago (2.1) from about 25 miles away?

I've gotten sick buying every antenna in the store and nothing works. I'm ready to try and build something myself.

Doggie. From what a friend in Chicago says, everyone is sick and tired of buying antennas for WBBM. (2.1) RF#3. Things are not going to get better either. WLS is returning to RF7. They BOTH will be at low power.
EDIT: Sorry, I did not answer your question. IMO a homebuilt antenna for RF3 is huge & difficult to make. You are going to need a VHF yagi on a rotor. Multi path is your biggest problem. A highly directional antenna pointed just right is your best bet.

Bob 61231
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post #3 of 57 Old 04-30-2008, 07:33 PM - Thread Starter
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Quote:
Originally Posted by spokybob View Post

Doggie. From what a friend in Chicago says, everyone is sick and tired of buying antennas for WBBM. (2.1) RF#3. Things are not going to get better either. WLS is returning to RF7. They BOTH will be at low power.
EDIT: Sorry, I did not answer your question. IMO a homebuilt antenna for RF3 is huge & difficult to make. You are going to need a VHF yagi on a rotor. Multi path is your biggest problem. A highly directional antenna pointed just right is your best bet.

I've gotten sick of buying and returning every type of indoor amplified antenna and none get CBS 2.1.

CBS should increase broadcast power. I can't even get a signal. Doesn't CBS want viewers? How can they sell advertising if nobody can get their station?
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post #4 of 57 Old 04-30-2008, 08:57 PM
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Quote:
Originally Posted by doogiehowser View Post

I've gotten sick of buying and returning every type of indoor amplified antenna and none get CBS 2.1.

CBS should increase broadcast power. I can't even get a signal. Doesn't CBS want viewers? How can they sell advertising if nobody can get their station?

What is the - dBm of this station? Just curious if it is under -60
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post #5 of 57 Old 04-30-2008, 09:10 PM - Thread Starter
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Quote:
Originally Posted by lexus2108 View Post

What is the - dBm of this station? Just curious if it is under -60

3.7 Xmit(kW) -55Rx(dBm)
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post #6 of 57 Old 05-01-2008, 07:36 AM
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Forget about trying for WBBM until they move to 12 next year. Getting RF 3 is a nightmare in Chicago. Have a look at the local Chicago thread for more info.

As for indoor VHF antennas with gain (directionality), even achieving that for upper VHF is very difficult (unless you don't mind a 100" boom in your room). Attic VHF antennas are about the only "indoor" solution that will have any gain.
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post #7 of 57 Old 05-01-2008, 08:34 AM
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Quote:
Originally Posted by doogiehowser View Post

What is the best material to use to build an antenna? Copper? Aluminum? Steel?

Gold!

Quote:


Is it a good idea to put something behind the antenna to reflect signals towards the antenna? Like a sheet of shinny aluminum foil?

What is the best shape and legnth to get CBS HDTV in Chicago (2.1) from about 25 miles away?

I've gotten sick buying every antenna in the store and nothing works. I'm ready to try and build something myself.

Doogie, those indoor FM antennas that are made with twinlead (FM folded dipole), such as Radio Shack's Model: 42-2385
http://www.radioshack.com/product/in...entPage=family
are made for the FM band which falls between TV's high and low VHF bands.
So, they are almost the right dimensions for low VHF TV reception. You can find them for only a couple of bucks, if you'd like to try one out for Channel 2.
You'd need a 75 Ohm - 300 Ohm balun, as well. You may already own both items as stereo receivers used to include an FM antenna.

Do you have a window in the room with your TV that faces Chicago (more or less)? If so, try taking whatever indoor TV antenna you still have and placing it right in front of that window. I mean just inches in front. You may need a longer piece of coax for this experiment, and you may not want like the arrangement, but try it. I've found that (mainly for UHF - not VHF) even wood frame building materials block the signals more than one would hope.

Back to your original question about making an antenna for your situation:
A wire 3 element yagi taped to the ceiling pointed at Chicago, using a homemade twin-lead folded dipole tuned for 56 MHz as the center element
might do the trick. Cost? Less than $10.

Or google "6m moxon rectangle" and go from there. The problem is that antennas optimized for Channel 2 will be larger than those for the higher channels. That makes installation, orientation and appearance more of an issue than for the upper channels.
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post #8 of 57 Old 05-01-2008, 08:40 AM
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I should have pointed out that your basic rabbit ears with the elements fully extended and flat down to the sides is your starting reference antenna for Channel 2. Take one of those and move it around the place turning it broadside to Chicago for starters.

The corner reflector design you see in some UHF antennas could be adapted to VHF with a single element in front of the right-angled reflector. This would be a conversation piece in your typical room, I could promise you, however.
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post #9 of 57 Old 05-01-2008, 10:08 AM
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I built a folded dipole antenna for VHF high out of scrap antenna parts. It works really well and has been outside for almost 3 years now. I can't imagine how large it would be for VHF low, though.

David
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post #10 of 57 Old 05-02-2008, 04:31 PM
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DH - Don't know why this worked for me. Just got my HD TV and am using OTA. From NJ I am 30-35 miles from NYC's broadcasts. My CBS is also 2.1. It was my worst reception station too, until I pointed my antenna up about 20 degrees instead of horizontal. Didn't lose 4,5,7 (best reception),9,11 or 13
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post #11 of 57 Old 05-03-2008, 06:07 AM
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post #12 of 57 Old 05-03-2008, 07:32 AM
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OP Title says VHF, but sounds more like a UHF design is needed.

I built a single channel VHF for VHF CH#4: Measured for 1/2 wave-length (dipole), used twin-lead wire mounted horizontally on a fiberglass rod with no reflector. It works great. I don't recall the calculation (buried in my bookmarks somewhere), but the 1/2 wavelength math is simple and effective. e.g. can cut lengths specific to your channel requirements for very little cash and better performance than store bought models.

For UHF, my local TV station was giving away the CM4228 which works measurably better than a CCM3221. Their both simple bowtie designs.

Here's a link which got me started, with lots of good links (lumenlab forum).
http://www.lumenlab.com/forums/index...antenna&st=100

hth
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post #13 of 57 Old 05-03-2008, 09:00 AM
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Quote:
Originally Posted by mark21ray View Post

From NJ I am 30-35 miles from NYC's broadcasts. My CBS is also 2.1. It was my worst reception station too, until I pointed my antenna up about 20 degrees instead of horizontal. Didn't lose 4,5,7 (best reception),9,11 or 13

There's no digital broadcast in NYC in the VHF-Lo band. That 2.1 is a virtual channel; I believe that station is actually on UHF.

Chicago has a digital station that's really in the VHF Lo band, which is a whole different animal (and probably not one worth chasing, since it's moving)
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post #14 of 57 Old 05-03-2008, 07:04 PM
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Attached is my 1st attempt to construct an upper VHF bow-tie antenna. It is a single bay for now, but seems to be performing well.

These are 6' ceiling support wires that I have bent to form the whiskers. However, as each side is about 35.5", I could probably shorten them a bit. At this length, it puts them below channel 7, if my calculations are correct.

Attached are some analog VHF screens, but it did fairly well for some UHF channels as well. I don't have any local VHF DTV stations to test it on yet. I also have not tried it with the 7777 as yet, which is currently connected to my YA1713.
LL
LL
LL
LL
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post #15 of 57 Old 05-03-2008, 07:25 PM
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Good job with the antenna and photos, Mike. Thanks for the link sending me here.

If you can not measure it, you can not improve it.
Lord Kelvin, 1883
www.megalithia.com/elect/aerialsite/dttpoorman.html
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post #16 of 57 Old 05-03-2008, 09:03 PM
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Google on the phrase "A simple, efficient TV antenna" and look at the wfu.edu link. This short article will give you the formulae for calculating folded dipoles tuned to what you want to receive.

From the article:

"For channels 2 - 4, the frequency is given by
f (in MHz) = (6 x channel_number) + 45."

Edit: This article also gives you the info for making reflectors and deflectors. You can use electric fence wire for those. All this would look like a real piece of work stapled to your ceiling but you'll probably be able to watch channel 2.
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post #17 of 57 Old 05-04-2008, 07:54 AM
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Quote:
Originally Posted by n4yqt View Post

You should tune the length of each side to the resonant length of 196 Mhz

That is about 28.6", correct?
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post #18 of 57 Old 05-04-2008, 08:02 AM
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Quote:
Originally Posted by n4yqt View Post

Thanks, David. Good job!

It was pretty easy to compute using a ~30 inch boom which is what I had saved for an end launch antenna. The computations showed I needed one reflector and two directors for about 6.5dB of gain. It complained that my antenna was too short, but I was willing to make that compromise. It is short and strong enough to have survived the 60-80MPH winds we have had on a few occasions around here.

The folded dipole part was made out of a piece of 1/2 inch wide aluminum
strip I found at Lowes. I just folded it around a piece of wood I cut to the calculated dimensions.

David
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post #19 of 57 Old 05-10-2008, 06:51 AM
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Quote:
Originally Posted by n4yqt View Post

Check out this calculator page:

http://www.csgnetwork.com/freqwavelengthcalc.html

A quarter wavelength is 15" and a half wavelength is 30"

The 30" VHF version I built is working quite well in the attic. It even produces a "viewable" picture for some of the Low-VHF stations, at least until I put on my glasses.

As it's bi-directional, I may keep using it in place of the YA-1713 to get San Diego 8 and 10 (at least on tropo days).
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post #20 of 57 Old 07-12-2008, 03:25 PM
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I don't know if anyone is still monitoring this thread, but I thought I'd offer my cheapo temporary solution - a kluged quad antenna.

I took two pairs of rabbit ears. I designated one as the lower half and attached it's twin lead (via a 300-to-75 balun) to the coax for the TV. Using the thickest sections of the rods, I extended each arm to 17.25" and positioned them 90 degrees apart.

I unscrewed the arms from the second set of rabbit ears, discarded the plastic connector/holder, and screwed the arms directly together at a 90 degree angle. Each of these arms was also extended 17.25".

The tips of the bottom half and the top half are held together with several turns of rubber bands. The final result looks like a diamond (i.e., like a square sitting up on a corner). I made a mount for it using some dowels and wood blocks. This beauty sits on top of the TV hutch.

The antenna performs amazingly well. I can get good digital reception of VHF and UHF stations 20 to 50 miles away. Even though the transmitters are positioned in two different "farms" separated by 51 degrees azimuth, I don't have to reposition the antenna at all. (Note that I'm in nice, flat, high-rise-free Florida, ZIP code 33803.)

I'm currently trying to design a 2 element quad for even better reception. (The new design won't be a kluge job though...)

Jean
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post #21 of 57 Old 07-12-2008, 04:02 PM
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Quote:
Originally Posted by CJLS View Post

I don't know if anyone is still monitoring this thread, but I thought I'd offer my cheapo temporary solution - a kluged quad antenna.

I took two pairs of rabbit ears. I designated one as the lower half and attached it's twin lead (via a 300-to-75 balun) to the coax for the TV. Using the thickest sections of the rods, I extended each arm to 17.25" and positioned them 90 degrees apart.

I unscrewed the arms from the second set of rabbit ears, discarded the plastic connector/holder, and screwed the arms directly together at a 90 degree angle. Each of these arms was also extended 17.25".

The tips of the bottom half and the top half are held together with several turns of rubber bands. The final result looks like a diamond (i.e., like a square sitting up on a corner). I made a mount for it using some dowels and wood blocks. This beauty sits on top of the TV hutch.

The antenna performs amazingly well. I can get good digital reception of VHF and UHF stations 20 to 50 miles away. Even though the transmitters are positioned in two different "farms" separated by 51 degrees azimuth, I don't have to reposition the antenna at all. (Note that I'm in nice, flat, high-rise-free Florida, ZIP code 33803.)

I'm currently trying to design a 2 element quad for even better reception. (The new design won't be a kluge job though...)

Jean


Nice reuse of materials. As long as they do signals then antennas can look how ever they look.

Will you try making two spreaders, support for element, on a boom and use wire for elements?

Would be interested in your posting what you do.
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post #22 of 57 Old 07-13-2008, 02:13 PM
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The plan is to make a square quad with #10 copper wire. I'll make a custom stand with a 12"x1" boom, and I'll use 1"x1" crosspieces to attach the loops to the boom.

I investigated a lot of potential designs, but the square quad gave the most bang for the buck in a realtively small size. I came to these forums hoping for some other options, but everybody seems to be focused on DIY antennas for UHF ...sigh...
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post #23 of 57 Old 07-13-2008, 02:25 PM
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Quote:
Originally Posted by CJLS View Post

The plan is to make a square quad with #10 copper wire. I'll make a custom stand with a 12"x1" boom, and I'll use 1"x1" crosspieces to attach the loops to the boom.

I investigated a lot of potential designs, but the square quad gave the most bang for the buck in a realtively small size. I came to these forums hoping for some other options, but everybody seems to be focused on DIY antennas for UHF ...sigh...

UHF is where most of the DIY action is because they are smallest and easiest, most people lack good enough antennas for that band at least for DTV, that's where most DTV is now and will be in the future.

I will have three stations hi VHF after the transition in two directions, so I'll be looking to having two antennas to homebrew.
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post #24 of 57 Old 07-13-2008, 04:41 PM
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Quote:
Originally Posted by n4yqt View Post

What polarity type do TV stations transmit - Circular or Horizontal? (Obviously not Vertical but I could be wrong.) If Circular, left hand or right hand circular polarization?


Horizontal Polariztion.

John
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post #25 of 57 Old 07-13-2008, 07:15 PM
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When you build your quad, consider building it round instead of square. The round shape is seldom used but is the best for gain. The construction can be more difficult but at VHF-HI frequencies, it should be easy to do with #10 wire or some small diameter tubing. Just feed it directly from the bottom for horizontal polarization just like the square ones.
If you make it out of something like 3/8" tubing it can be made slightly smaller in diameter and will have a greater bandwidth.
There are tons of web sites that have calculators for making quads. You can just plug in the desired frequency and size of the material you want to use and it will give you the length you need.
One caution on adding elements, when you start adding elements to a quad you start to lose bandwidth very fast. Everything is a trade off in general more gain = bigger antenna or less bandwidth or both.

Here is a link to a post on dimensions for a 2 bay bow tie for VHF-HI for anyone interested. http://www.avsforum.com/avs-vb/showt...8#post14245728

They're very forgiving to slight construction deviations just are sure to keep the phasing lines spaced away from the main support using some non-conductive mounting blocks of some sort.

In addition, a 4 bay UHF has slightly more gain than a single element quad on VHF-HI with the added bonus of good gain on UHF.

None of these antennas will work worth a hoot on VHF-LO
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post #26 of 57 Old 07-14-2008, 09:26 AM
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Quote:
Originally Posted by mclapp View Post

When you build your quad, consider building it round instead of square. The round shape is seldom used but is the best for gain. The construction can be more difficult but at VHF-HI frequencies, it should be easy to do with #10 wire or some small diameter tubing. Just feed it directly from the bottom for horizontal polarization just like the square ones.
If you make it out of something like 3/8" tubing it can be made slightly smaller in diameter and will have a greater bandwidth.
There are tons of web sites that have calculators for making quads. You can just plug in the desired frequency and size of the material you want to use and it will give you the length you need.
One caution on adding elements, when you start adding elements to a quad you start to lose bandwidth very fast. Everything is a trade off in general more gain = bigger antenna or less bandwidth or both.

Here is a link to a post on dimensions for a 2 bay bow tie for VHF-HI for anyone interested. http://www.avsforum.com/avs-vb/showt...8#post14245728

They're very forgiving to slight construction deviations just are sure to keep the phasing lines spaced away from the main support using some non-conductive mounting blocks of some sort.

In addition, a 4 bay UHF has slightly more gain than a single element quad on VHF-HI with the added bonus of good gain on UHF.

None of these antennas will work worth a hoot on VHF-LO

I modelled and tested (via 4nec2) a circular quad, but the width of the antenna was unacceptable for the final location. I also tested diamonds with different (vs the usual 90 degrees) interior angles, rectangular quads - any shape I could dream up! The most powerful puppy was a 2-bay whisker array ....but gees, that antenna was huge!

I abandoned the web site calculators in favor of using 4nec2, which has options available to optimize gain for the whole VHF band gain.
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post #27 of 57 Old 07-14-2008, 02:58 PM
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Quote:
Originally Posted by CJLS View Post

I modelled and tested (via 4nec2) a circular quad, but the width of the antenna was unacceptable for the final location. I also tested diamonds with different (vs the usual 90 degrees) interior angles, rectangular quads - any shape I could dream up! The most powerful puppy was a 2-bay whisker array ....but gees, that antenna was huge!

I abandoned the web site calculators in favor of using 4nec2, which has options available to optimize gain for the whole VHF band gain.

You could try a 2 bay with a triangle elements instead of wiskers the gain is only slightly less but it shortens the width by quite a bit.

It would still be near 40" wide for VHF-HI. I'm sure it would still be is too wide still since a round loop made from 1/4 diameter tubing for vhf-hi is only about 25" wide.

I guess it's hard to get something (gain) for nothing (space).

I have a triangle shaped quad for HF 14,18,21,& 28 mhz
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post #28 of 57 Old 07-15-2008, 02:34 PM
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Quote:
Originally Posted by mclapp View Post

You could try a 2 bay with a triangle elements instead of wiskers the gain is only slightly less but it shortens the width by quite a bit.

It would still be near 40" wide for VHF-HI. I'm sure it would still be is too wide still since a round loop made from 1/4 diameter tubing for vhf-hi is only about 25" wide.

I guess it's hard to get something (gain) for nothing (space).

I have a triangle shaped quad for HF 14,18,21,& 28 mhz

As per your suggestion, I revisited the circular and octagonal loop designs. When 4NEC2 atempts to optimize them, it ends up with the reflector being smaller than the driven element. Mathematically it appears to work well, but in the real world would it work, and if so, why?

I tried to model a 1 bay triangular antenna for VHF. The gain was great, but the pattern (huge side lobes and a smaller center lobe) was not the best for me since I have to aim the antenna mid-way between the two transmitter locations (one 20 miles away at 236 to 240 degrees, and the other 50 miles away at 285 degrees).

Another burning question: on a square loop, how large should the feedline gap be? None of the writings I've seen on the web address this question.

Jean
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post #29 of 57 Old 07-18-2008, 10:47 AM
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Quote:
Originally Posted by CJLS View Post

As per your suggestion, I revisited the circular and octagonal loop designs. When 4NEC2 atempts to optimize them, it ends up with the reflector being smaller than the driven element. Mathematically it appears to work well, but in the real world would it work, and if so, why?

I tried to model a 1 bay triangular antenna for VHF. The gain was great, but the pattern (huge side lobes and a smaller center lobe) was not the best for me since I have to aim the antenna mid-way between the two transmitter locations (one 20 miles away at 236 to 240 degrees, and the other 50 miles away at 285 degrees).

Another burning question: on a square loop, how large should the feedline gap be? None of the writings I've seen on the web address this question.

Jean

I see what your saying about the round loops and the smaller reflector, it must be something with NEC2 or the way we are modeling them.

The square loops model as expected with a slightly larger reflector.

I have built round loop quads for 144 mhz and they work great using the normal configuration of a larger reflector.

A 1 bay (2 triangles fed in the center) should have a figure 8 pattern at the design frequency normally.
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post #30 of 57 Old 11-10-2008, 12:12 AM
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Quote:
Originally Posted by n4yqt View Post

What polarity type do TV stations transmit - Circular or Horizontal? (Obviously not Vertical but I could be wrong.) If Circular, left hand or right hand circular polarization?

Currently 6.2% of TV stations reportedly broadcast Circular, Elliptical or Slant Polarization.
WPTV in West Palm Beach plans Elliptical Polarization in Feb when they move to Ch12.
See FCC TVQ dBase for details:
http://www.fcc.gov/fcc-bin/tvq?list=0&facid=59443

Use pull-down menus to find West Palm Beach in Rabbit's spread sheet:
http://www.rabbitears.info/ss/
However, it seems "CP" includes both EP and SP.

Doug Lung has a recent articles on adding a vertical component to the
usual horizontal polarization....and receive antennas:
http://www.tvtechnology.com/article/67946
http://www.tvtechnology.com/article/68820
Note he cites FCC requirement for RIGHT HAND, if circular polarized.

Post-Feb2009 filings show 13.7% with at least some vertical polarization.
Many more are likely to facilitate ATSC-M/H coverage (upcoming in 2009)
to cars/buses/trains with whip antennas.....and handheld devices.
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