We'll see how it works when we get everything hooked up on the radio end.
I finally decided to expand out of the VHF/UHF bands into HF. I wanted an "invisible" antenna, so I'm starting with an attic mounted G5RV antenna. The junior version from MFJ that covers 40 meters through 10 meters on the ham bands. Antenna mounted as high as practical. You can see it's clear of metal objects and the ladder line goes off to the right at a 90 degree angle. Not ideal, but I'm avoiding routing it near any air ducts and wiring in the attic. Since I have a hip roof, the radials are bent down. The supports are wire tie loops supported with nylon twine. This radial gets the closest to metal. The foil on the ducts may cause the antenna to have a null or contribute to an unwanted noise gain. You can see the end insulator, again supported with twine. And the duct work I'm trying to avoid. Here is the ladder line to coax transition. This was my first time installing a UHF connector on coax. It turned out neat with the blue heat shrink. Also, since this is a balanced multi-band antenna (not usually reasonant), MFJ recommended constructing a balun by looping the coax. This is 10 loops around 5" in diameter. The function of the loops is to provide high impedance to any common mode current. Ideally, in a balanced antenna, balanced feed line, all of the current would be differential mode. That is the current on the coax shield would be equal and in opposite direction from the current on the center conductor. If that's the case, the loops will not add impedance to the current and all the energy is radiated by the antenna. However, any current on the shield in addition to the differential mode current would see the inductance of the loops. That inductance helps to prevent and minimize common mode currents. You don't want common mode currents because they add to the noise of reception and can cause problems during transmission. This is because the common mode currents cause the coax to act as an antenna, and some of the energy is radiated by the coax shield instead of the antenna.
We'll see how it works when we get everything hooked up on the radio end.
3 Comments
6/25/2018 01:03:29 pm
Jonathan,
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Xu
1/30/2021 05:48:50 pm
Dear Sir, I am newly getting into HF and just ordered the G5RV, Jr antenna for attic installation. I have an exactly same attic on top of the second floor of the house. With HOA and everything, the attic seems to be the only logic place to install the the antenna. So, would you please let me know how the antenna in attic worked out for you. Any information on this matter will be highly appreciated. Thank you very much! God bless !
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Jonathan Weaver
3/4/2021 11:55:55 am
It works well. I kept it as straight as possible. I have a hip roof, so it goes along on hip, then across the top, and then down the next hip to the opposite corner of the house. The only downside is interference with a touch lamp in the dining room (the lamp flickers when I key up).
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AuthorHusband. Father. Electrical Engineer. Electronics and woodworking hobbyist. Archives
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