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Author Topic: Loop antenna setup and use  (Read 2117 times)
KF7ZCH
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Posts: 13




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« on: January 03, 2013, 06:55:07 PM »

I am a new general class operator.  I have gotten a new hf radio and I want to put up an antenna.  On my roof a loop antenna would be preferable.  I want to consult anyone on eham.nets forums to help me.  My proposed idea is as follows:  I want to make an 80 M loop.  I want feed it with ladder line or something similar, have a balun and have coax to my antenna tuner then to my radio.  I would like to know if this is a decent setup or if the effort, at least on my roof, to get a dipole up is worth the effort.  Can my setup produce low swr and get a fair amount of my rig's 100 watts to the antenna?  If this antenna system works, what kind of balun would I use.  Responses are greatly appreciated.  I am open to people's ideas and responses. Thank you.

KF7ZCH
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AC2EU
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Posts: 366


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« Reply #1 on: January 04, 2013, 08:49:18 PM »

There was a recent discussion of a loop antenna under the antenna forum heading recently. Take a look at that or do a search  of the site.
Any time you have an antenna in close proximity to another structure, there can be deleterious effects.
That's true for ladder line as well.

In the event that you can't find the info that you are looking for here, you  might want to consider getting a copy of the ARRL antenna book. It has thorough discussions about most types of antennas and feed line configurations.

Jim
AC2EU
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KU3X
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Posts: 142




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« Reply #2 on: January 06, 2013, 06:46:29 AM »

You have given a good approach to the issue at hand. But, once you put the parallel feeders on the antenna, you can not expect a low SWR on all bands. There is a possible way to do it but you’d be better off taking this approach:
From your loop run you parallel feeders to the 4:1 Guanella Current Balun. From that point run coax to your tuner. Put the tuner as close as you can to the balun. From that point on you can run
any length of coax needed to the radio. The coax from the tuner to the rig should have a very low SWR and the losses will be minimal. You should be able to operate on all bands from 80 meters up. If the tuner won’t work on a band or two, add or subtract some parallel feeder.
Depending on the feed point impedance of the loop, putting either a 4:1 or a 2:1 balun at the feed point can sometimes yield a low SWR on numerous bands. Then you can run coax from the loop to the rig. I used a 40 meter delta loop, fed with a 2:1 balun and it loaded with a very low SWR on 10, 15, 20 and 40 meters. It was erected vertical. The radiation pattern on 20 meters was straight up. Not what I wanted. But for you, seeing you are going to lay the antenna on its side, it won’t make any difference.
                     
Good luck with your project,
Barry   www. ku3x.net
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WA9CFK
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Posts: 87




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« Reply #3 on: January 29, 2013, 01:03:50 PM »

I have an 80 meter loop with the top on a tower at 45 ft, the bottom at 6 feet.

The sides are behind the tower about 15 feet and tied off in the tree line and as you can imagine it is more of an elongated diamond then a square.

I feed the top corner with 450 ohm ladder from my operating desk on any band except 160 with a simple MFJ 971 tuner at 100 watts.

It is anybody’s guess what the pattern looks like but it is what I had to work with. I like the loop because it is quiet and it serves me well for casual chatter. It probably is not what you want for serious DX.     
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