RF ground: long wire or counterpoise? - Elmers Forum at eHam.net

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RF ground: long wire or counterpoise?	Reply
by KB1KQI on February 3, 2004	Mail this to a friend!
My shack resides on the 2nd floor of my condo and my "antenna farm" is located in the attic (no outside antennas allowed, sigh). I am up and running on 2m, but plan on adding 6m and HF (still learning CW), probably 40-10m. Should I run an almost 60 foot RF ground wire to the basement and from there outside to a ground rod, or are multiple counterpoises a better option? Perhaps both? 73 de Jim KB1KQI

RE: RF ground: long wire or counterpoise?	Reply
by N9VKC on February 3, 2004	Mail this to a friend!
Greetings, I'm by no means an elmer lol however I've been looking into RF grounding in my limited situation as well. Have you given any thought to an artificial ground? MFJ makes one. I've been lookin to that for a rf grounding solution. I haven't tried it yet but when if I do I will let you know. 73 Chris

RE: RF ground: long wire or counterpoise?	Reply
by AG4DG on February 3, 2004	Mail this to a friend!
The need for an RF ground rod is an old spouse's tale. (The ground rod may be necessary for a safety ground or lightning ground, however.) Even if the RF ground rod were necessary, the wire connecting it to your rig would act as part of the antenna system, especially if the wire is around 1/4 wavelength long. Some better ideas: 1. Try attaching those 1/4 wavelength wires to the FEEDPOINT of the antenna grounds. 2. Use baluns at the antenna feedpoints. 3. Add ferrite chokes to the feedline. The feedline chokes add a large inductive reactance to the surface of the outer coax shield. The RF current is supposed to be on the inner surface of the coax shield, but under certain circumstances (like if the antenna has a poor ground plane), there will be an RF current being conducted on the outer surface of the coax shield. This "common mode" current will cause the coax, the chassis of your rig, your microphone, etc. to radiate. This is RF feedback, and this is what causes "mic bite".

RE: RF ground: long wire or counterpoise?	Reply
by AC5E on February 3, 2004	Mail this to a friend!
Well, there are plenty of opinions, but I have had no trouble with RF in the shack when I run the coax to ground level, through one of Radio Works "line isolators" (A grounded ferrite "current balun") then through a good quality ground rod mounted lightning arrestor. This seems to give a very positive stop to any RF coming down the outside of the coax. The worst case MEASURED RF on the feedline in the shack is less than 1 ma with about 1300 W CW out of a Centurion, and that's probably RF pickup rather than reflected from the load RF. The results are satisfactory for my operations at any rate. FWIW I generally use three rods in line connected with #4 or larger - smaller number - and mount the lightning arrestor on the center rod. It seems to be a better RF ground than the house full of iron water pipes I used a half century ago at any rate. 73 Pete Allen AC5E

RE: RF ground: long wire or counterpoise?	Reply
by AA4PB on February 3, 2004	Mail this to a friend!
A 60-foot ground wire is not an RF ground. If you use an unbalance antenna like an end-fed wire or a 1/4 wave vertical then you need an RF ground directly at the base of the antenna (such as 1/4 wave radial wires). If you use a balanced antenna such as a dipole then an RF ground is not required for the antenna. You can often get by with a choke or current balun in the coax to keep currents off the shield and even that may not be needed in some installations. In either case you should not need an RF ground at the radio.

RE: RF ground: long wire or counterpoise?	Reply
by KB1KQI on February 4, 2004	Mail this to a friend!
Thanks for all the comments regarding RF grounding. It looks like I will require a good choke balun at each of my antennas to keep the common mode current out of my shack. 73 Jim KB1KQI

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