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Full wave loop questiom




 
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April 13, 2021, 06:57:41 AM *
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Author Topic: Full wave loop questiom  (Read 281 times)
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WA2SQQ
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« on: April 07, 2021, 07:10:28 PM »

I like experimenting with wire antennas. I have antennas for all bands except 17m. I had an idea to create a full wave loop mounted around the perimeter of my garage roof. Im going to use 5 electric fence wire insulators to suspend it above the roof. I plan to feed it with open wire for about 10 ft and use either a 2:1 or 4:1 balun to connect it to the 7/8 hardline that feeds my antenna switch at the tower base.

Heres my question. Would I be better off build it for 17m, or should I use the maximum length possible (abt 78 ft) and be able to use it on other bands?
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Tom WA3KLR
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« Reply #1 on: April 07, 2021, 07:42:34 PM »

I think it would be a lot better to put a 1/4 wave vertical on the garage roof. Is the roof sheet metal?
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73 de Tom WA3KLR  AMI # 77   Amplitude Modulation - a force Now and for the Future!
WA2SQQ
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« Reply #2 on: April 08, 2021, 07:58:34 AM »

No its not metal. This is more about experimenting with wire antennas.
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W4AMV
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« Reply #3 on: April 08, 2021, 09:03:38 AM »

Hello,

Use any of the NEC programs, 4NEC, EZNEC, AWAS and in about 20 minutes or so you can look at both configurations. The wire antenna programs are pretty good, not perfect but really close, depending on you model inputs. Sketch out your configurations, square, rectangle, lengths, etc... and will try to input as time permits. You will get pattern, Zin, and can play with operating frequency, matching and loading without climbing out on the roof!

Alan
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w9jsw
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« Reply #4 on: April 08, 2021, 10:25:23 AM »

I am going to try a 29ft. vertical doublet for 17M. I have some spare 300 ohm twinlead to play with. Won't be a QRO antenna! Will hang it from a branch and pull the twinlead off perpendicular to the antenna. May also load up for 15/12 and 10 if lucky.

John
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W4AMV
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« Reply #5 on: April 08, 2021, 11:41:08 AM »

Constructed a square loop 19.5 feet on a side. Up 25 feet. Feed at corner or center... no significant difference. At 25 feet up, the TO angle at 40 degrees and the gain is 5.5 dBi in the 17 meter band. The Zin is ~ 422 + j 1200 ohms. I used average ground terrain and assumed the roof has no influence. If you raise above 25 feet, you
begin to see secondary lobe at the zenith. I did not investigate other bands. This arrangement is easy to match.

Should add, easy to do, trim to the band center and Zin resonant at 125 ohm + j7...
the TO angle down at 35 degrees and the gain at ~7 dBi.

Alan
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WU2D
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CW is just a narrower version of AM


« Reply #6 on: Yesterday at 07:36:46 AM »

I like vertical loops because they are quiet on receive when fed for horizontal (bottom center). My largest was a full sized 80M pulled way up into 125' pines. Almost perfect square. Yup I did the 4:1 Balun thing with a big 200 Ohm resistor up top center and she gave wonderful performance on 80, 40 and 20 with no tuner. Yes loss of course with power wasted, but no fuss.

Presently, I have a 20M vertical loop up,and I fed it with a quarter wave section of 75 Ohm off the hardline for a single band.

So for a multiband, hardline and a good tuner, just cut the loop for the lowest band you want to work, and you may be surprised how it works on other bands. Or nest in a second loop, same feed, on the problem band.

Mike
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