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Old 2011-11-30, 01:51 PM   #31
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Quote:
How would this loop do with circularly polarized broadcasts? Wondering if it would do better than a horizontally polarized antenna.
It would do great. The radiation pattern is like a bubble.
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Old 2011-11-30, 02:06 PM   #32
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That is what I was hoping. Now the scary part. How large would it need to be to receive channel 6.
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Old 2011-11-30, 02:48 PM   #33
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Thinking more about it, since circular polarized broadcasts have a 1/4 wavelength (90 degrees) phase difference between the horizontal and vertical components, you will only get 1.5dB gain over an equivalent horizontally polarized antenna. To achieve the full 3dB of gain, you would need an make it into a spiral instead of a loop, but then the reflector would need to be a spiral (not sure how to make that). You would also need to know it the broadcast has a clockwise or counterclockwise twist.

This is getting off topic, but we may be better off building an antenna designed for circular polarized broadcasts, like the modified cubical quad design shown here (assuming Global doesn't change channels).
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Old 2011-11-30, 04:06 PM   #34
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A top or bottom-fed Loop has MINIMAL response to Vertical Polarized signals....and
a side-fed Loop has MINIMAL response to Horizontal Polarized signals.

To see H, V & Total Gain responses, in 4nec2's PATTERN box, under "Far-field", enable
"Show Multi-pattern"...or just hit the "M" key.

===========================================================
RabbitEars tracks status of Circular ("C") and Elliptical ("E") Polarized Station (U.S. Only):
http://www.rabbitears.info/oddsanden...ization&type=C
http://www.rabbitears.info/oddsanden...ization&type=E

===========================================================
K6STI's analysis Circularly Polarized Quadix, Cubical Quad, Loop & Rabbit-Ears FM Antennas:
http://www.ham-radio.com/k6sti/
Can Rescale to Lo-VHF, Hi-VHF or UHF Bands....

===========================================================
Two alternative designs for Hi-VHF 5.5-Turn (103-in) Helical Antennas with FLAT (NOT Spiral)
Reflectors can be found here, if you are interested in DIY Circular Polarized antennas:
http://imageevent.com/holl_ands/circularpolarized
I included some design references if you want to do your own design (good luck....)

If you're interested in longer, higher Gain, narrower bandwidth alternatives,
try adding more turns to the above....
Or try to copy one of the fol. Wade Helical Antenna designs:
http://www.wade-antenna.com/Wade/WH14-69.pdf
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Old 2011-11-30, 04:19 PM   #35
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Quote:
but then the reflector would need to be a spiral (not sure how to make that).
Not that hard. You would need to mark out a spiral on the mesh and then cut it and push the center forward. Try it on a piece of paper.
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Old 2011-11-30, 06:49 PM   #36
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Quote:
That is what I was hoping. Now the scary part. How large would it need to be to receive channel 6.
Not sure where your channel 6 is in relation to you, but the RF6 that is close to me is 27 miles out...almost 10 miles closer than RF13 that I was gunning for, yet I can't get a whisper from it. Two things: 1) the antenna would most likely need to be a little larger, and 2) I think that RF6 CIII is transmitting at a pretty low power...much like all the VHF stations.

According to TVFool, I shouldn't really have much of an issue in getting 6, and it is almost in line with RF13. Oh well, doesn't really matter since I'm getting CIII from Toronto just fine on RF41.
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Old 2011-12-01, 11:10 AM   #37
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I am not surprised you aren't able to receive RF6 with your loop as it has a centre frequency of 95 MHz compared to the centre frequency of 213 MHZ for RF13. I am assuming to tune it for RF6, it would need a diameter of about 6 feet (about 3X the diameter of your 23" loop). That would make the circumference close to 19 feet (an awful lot of copper tubing). Probably not feasible.
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Old 2011-12-01, 01:32 PM   #38
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You could use AWG10 if you only need enough bandwidth for Ch6, which would be easier
to construct if it were a Square Loop:
http://imageevent.com/holl_ands/loops/vhfloop
Rescale Hi-VHF (16.75-in if AWG24) size LARGER by Factor=198/85=2.33 or 39-in per side.

If you were to use a Reflector Screen, the Separation distance would be 2.33 x 13in = 30.3-in,
with a Screen size of at least 2.33 x 28in = 65-in x 65-in. AWG10 or AWG12 wire could be
strung horizontally (only) between outer box supports at say 8-in separation between each rung.
No need to string vertical wires, other than you could conveniently move to the next rung at each end....
loops don't have any meaningful vertical polarization response.
http://imageevent.com/holl_ands/loop...squarelooprefl
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Old 2012-05-17, 08:29 PM   #39
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Hi all,

I also build this antenna. I build this for hi-VHF. But it is also catching UHF channels from Toronto and Buffalo as well. I installed it in my attic. No reflector yet. It is catching Barrie CKVR and Hamilton CHCH from opposite directions. I am getting 70% signal on both. But when I try to amplifi with Kiztech it reduces to 60%. I don't know why ?

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Old 2012-05-17, 11:32 PM   #40
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Quote:
It is catching Barrie CKVR and Hamilton CHCH from opposite directions.
Yep, without a reflector, its bi-directional.

Quote:
I am getting 70% signal on both. But when I try to amplifi with Kiztech it reduces to 60%. I don't know why ?
Possible overloading, or youre amplifying a multipath signal which is common in an attic.
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Old 2012-05-20, 01:12 PM   #41
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Thanks 300ohm. Any solutin for multipath ? Can multipath happen even if i use only one antenna ?

Thanks

Last edited by meridish; 2012-05-20 at 02:33 PM.
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Old 2012-05-20, 11:45 PM   #42
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It depends on the direction the multipath is coming from. If its from the back, then a reflector would help, but there goes the bi-directionality.
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Old 2012-06-20, 11:32 AM   #43
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So I built one of these and tried it out to see if it would out perform my stacked 2 * rca751's unfortunately it did not. Will try different placement etc and keep you posted.
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Old 2012-08-04, 05:13 PM   #44
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Default I wouldn't have believed it

Thanks to all of you for your great work and pointers. I'm getting ready to dump my local cable provider, going back to strictly OTA. And of course I live in a basement apartment in a valley, 35 to 40 miles from the "local" towers. The apartment complex rules say I can't put anything outside...so it has to be something indoors. Nothing I bought retail would work. Worked great for the UHF signals, but couldn't pull in the two local VHF-high channels. After reading though this thread, I went down to the local Menards, picked up some PVC and 1/4 inch copper tubing and built a quick and dirty free-standing version of this antenna. No reflector, just the loop. Hooked it up to my existing 24db amp, and the results were nothing short of amazing. Where I had no VHF signal before, I was pulling in the farthest station at 38% signal and 85% quality. Very usable. The nearer VHF station was 68% signal and 100% quality. Even pulled several of the UHF stations with this. So a small UHF loop to pull in the missing stations, and I'm there! All this in my basement apartment, thick concrete walls and all. I'm well and truly impressed.
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Old 2012-08-04, 11:11 PM   #45
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Quote:
So a small UHF loop to pull in the missing stations, and I'm there!
Don't forget, youll need a Uhf-Vhf Signal Joiner, UVSJ for short unless your preamp has separate inputs.

I would build a bit higher gain uhf antenna than a loop for uhf.
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