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Author Topic: Feeding a Gem Quad with ladder line?  (Read 1482 times)
W5REO
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Posts: 10




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« on: August 08, 2006, 08:13:55 PM »

I went to my local ham store and was discussing feeding a 2 element, 5 band quad. It was suggested that a quick and cheap way to get on the air would be to tie the ends of the loops together and feed the antenna with 450 ohm ladder line connected to a 4:1 balun and use a tuner to load up the antenna. I know that I may loose some power into the non-resonant loops, however, this is not a permanent setup. Has anybody had any luck with something like this?

Eventually, I plan to install a remote antenna switch and feed each loop individually. But for now, I just don't have the $$$ to do so.

Thanks for the advise!!!

W5REO
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N4FD
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Posts: 1




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« Reply #1 on: August 09, 2006, 05:27:14 AM »

I have done this before with just ladder line and tuner-no balun. The quad worked fine. I don't know about losses in the loops. There may have been some interactions but the antenna played well for me.

Larry
N4FD
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N4IR
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« Reply #2 on: August 09, 2006, 06:06:52 AM »

I have had the tri-band Gem Quad at 60 feet for over 25 years (before the WARC bands) with all loops tied together through a 1:1 balun fed with RG-213. I did replace the original supplied balun with another a few years ago. It has earned a 5BDXCC and Honor Roll mixed and CW in that time. There is no interaction that I can see. A friend who also had one tried feeding the loops with individual coax with no discernible difference in performance. Keep it simple, go through the 1:1 balun with a single run of coax and enjoy. One note on quads in general, it doesn't matter how you feed them, how you tune them or what height you have them at, they all work quite well.
 
Jim, N4IR
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KP4DX
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Posts: 2




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« Reply #3 on: August 09, 2006, 12:41:46 PM »

After different configurations of Gem Quads, I have settled for a single 50 ohm coax to an antenna switch. From there, I am feeding each element via a 1/4 wave section of 75 ohm coax. I tried this feeding method after years of playing with quads. A single line of 50 ohm coax with a 1:1 balun will do just fine if you are not concerned with the potential of slightly high SWR although some people do not have high SWR problems.

Also in my case, I decide to only go for the 10/15/20 meters combination since I wanted to optimize for these bands.

The most bang for the buck with the two element quad will be the reflector tunning. I tried a simple idea I had never seen used before but it worked great. I used an MFJ SWR Analyzer to tune the reflector. I opened the reflector element, calculated the lenght of an antenna 5% longer than my target frequency and I fed the reflector element via a short coax with alligator clips. I then moved the clips up/down the stub until I saw the lowest SWR at the target frequency and soldered the shorting stub at that point.

I have a small diagram of this process and if you are interested, I would be more than happy to forward it to you.

73 and enjoy an awesome antenna.

Luis
KP4DX
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W5DXP
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« Reply #4 on: August 09, 2006, 01:09:45 PM »

> W5REO wrote: I went to my local ham store and was discussing feeding a 2 element, 5 band quad. It was suggested that a quick and cheap way to get on the air would be to tie the ends of the loops together and feed the antenna with 450 ohm ladder line connected to a 4:1 balun and use a tuner to load up the antenna. <

Don't know anything about the quad but all hams need to get over the idea that the 450 ohm Z0 of the ladder-line has anything to do with what impedance the tuner sees. If the quad feedpoint impedance is 50 ohms, the SWR on the 450 ohm ladder-line will be 9:1, the balun will NEVER see 450 ohms resistive, and the impedance seen by the balun will vary between 50 ohms and 4050 ohms usually with reactance. If the impedance seen by the balun is 50 ohms, a 4:1 balun will bring it down to 12.5 ohms. Why would anyone want to transform 50 ohms to 12.5 ohms? Unless one knows what impedance the balun is seeing, a 1:1 current-balun is the balun of choice.
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73, Cecil  http://www.qsl.net/w5dxp
 
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
W5REO
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Posts: 10




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« Reply #5 on: August 09, 2006, 02:37:08 PM »

Thanks for all the help; I really appreciate it. I think, for now, that I am going to back to the candy store and purchase a 1:1 balun, connect it to the elements, and feed it all with 50 ohm coax. Eventually, I will replace this with a remote antenna switch with individual feeds per band and include 6 meters as well.

Without an antenna analyzer, is there a way to tune the antenna for lowest SWR without running up and down the ladder and into the house or dragging the rig up onto the roof?
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K1XT
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Posts: 16




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« Reply #6 on: August 09, 2006, 02:40:01 PM »

Yes, feeding the quad with ladder line is a cheap way to go. Don't bother with a balun. You are feeding a balanced antenna with a balanced feeder. You'll have less loss too especially on ten meters. Try it and let us know how it goes. It's cheap and quick which is what you are looking for.

Bill k1xt
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W5DXP
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« Reply #7 on: August 12, 2006, 08:32:57 AM »

> W5REO : Without an antenna analyzer, is there a way to tune the antenna for lowest SWR without running up and down the ladder and into the house or dragging the rig up onto the roof? <

If you use ladder-line, you can tune the antenna *system* to lowest SWR without leaving the operating position. Such a feed method is described on my web page at: http://www.qsl.net/w5dxp/notuner.htm
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73, Cecil, W5DXP
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
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