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Author Topic: Loop and G5RV interaction?  (Read 709 times)
W8VZM
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Posts: 67




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« on: May 05, 2010, 03:17:59 PM »

Hello all!

Thinking about antenna installation at my new QTH. Initial install will be a 204' G5RV in the trees as an inv vee and a small vertical. Walking the dogs tonight I started thinking about a horiz loop. If the tree used as the center support for the vee was also used as a support (maybe feed point?) for the loop, what kind of interaction problems could I face? The tree in question has been chosen based upon height and ability to handle the ladderline and other feedline to the shack. I have plenty of others for support but getting the feedline to those trees could be problematic.

Ron W8VZM Central VA
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WX7G
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Posts: 6198




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« Reply #1 on: May 05, 2010, 03:31:52 PM »

One antenna will induce current in the other antenna. The unconnected antenna will modify the radiation pattern but not necessarily in a bad way. The feedline of the unused antenna can be left unconnected or shorted.
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VE3WMB
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Posts: 289




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« Reply #2 on: May 06, 2010, 06:39:48 AM »

Ron :

There will certainly be some interactions, exactly what is hard to say. It would be better if you could
get more separation between the two.  My advice is put up the 204 ft G5RV and try it out, you may find that the it works well enough that you don't need the loop. If you decide that you want to try the loop then
you will at least have had a chance to establish a bit of baseline on the G5RV with respect to what
bands it will easily load on etc and you will be in a better position to judge what, if any, detrimental effects the loop has on the G5RV.

I have a 204 ft G5RV up at my cottage. It is at about 45 to 50 feet up in a slight inverted vee configuration and I have found that performance is amazing on the higher bands. I have the added advantage of a hill top location (actually just slightly down one side of the peak of the hill) with the slope going about 300 feet down to a lake.
The combination of the physical size of the antenna and the terrain gives me very good gain and
a low take-off angle in the direction of the lake and I have easily been able to work into Asia (Japan, Asiatic Russia and Thailand) with excellent signal reports running only about 30W on CW on 20m and 17m recently.

I am using the Buxxcomm version of the 204 foot G5RV which is very well made and has been up two winters now with no damage to the antenna.
My advice is use a good quality coax run into the shack (I am using LMR400) and try to keep the coax run
as short as you can to minimize losses. With my LDG AT-100Pro tuner my antenna will match quite nicely on all bands from 160m through 6m with the exception of 80m, which seems to have become a bit problematic since I changed the antenna configuration slightly.  My plan is to install a backup antenna (likely an 88ft doublet) at a lower height and well away from the G5RV, to fill in the 80m gap and also give me a backup in case the G5RV comes down in the winter due to high winds (I am using trees as supports).
I have ruled out using verticals as a backup at my location as the soil is very rocky and it would be difficult
to get decent performance out of a vertical without a very extensive ground radial system.

Best of luck with antennas at your new location.

Michael VE3WMB

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W8VZM
Member

Posts: 67




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« Reply #3 on: May 06, 2010, 04:20:32 PM »

Michael,
Yes the 204' version is very nice I have had mine (TruTalk) in a similar configuration at my old QTH in Ohio. I will be picking it up on my return trip from Dayton next weekend. I especially like the lower noise level on the longer version. Without getting into too much detail The trees ring our property so I have many to choose from. The issue is trying to get the feedline out to the outer trees to feed the loop. I use 1/2" hardline to feed the G5 so losses are minimized. I was considering alternate antennas to add to my new "farm". 2.5 acres nearly square with house in the middle.Tower in the future after some thought about placement. Thanks for the input.

Ron W8VZM
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