On Sun, Oct 31, 2010 at 10:22 AM, Bill <w...@billnjudy.com> wrote: > It's called a counterpoise. > When all else fails, sometimes this works wonders. > Cut a length of wire (any kind, it doesn't matter) to the half wave length > for the band you wish to operate, and stretch it out on the floor, zigzag if > necessary. > Attach one end to the ground screw on the rig. >
You are right except it needs to be 1/4 wave, not 1/2 wave. An end-fed half-wave is a very high impedance. One or more pieces of wire cut to an electrical 1/4 wave it will help immensely. > This was another of the tricks my Elmer suggested for my 2nd floor shack, > right under the antenna mounted on the roof. > But someone made the really big and important point: one *must* stop the current from flowing. In fact, you probably DO NOT want your radios at RF ground. You want them to be at a point where the impedance is very high so that RF current is NOT flowing between the various boxes in the shack. This means that common-mode chokes are going to be more use than grounding. Grounding of your equipment is there for PROTECTIVE (keeping you from being electrocuted) reasons, not for RF reasons. Where you want to ground things is where your cables enter the building and the put common-mode chokes on the lines to keep RF currents from flowing in the boxes in the shack. DC ground is good for draining away DC charges. (Atmospheric voltage levels even a few feet above ground are surprisingly high.) But DC ground might not cut it if there is a lighting strike nearby. The current rise-time of a lightning discharge is *very* fast so it is really an RF pulse, not a DC event. This is why it is more accurately called an electro-magnetic pulse (EMP). For this you need to shunt the rising edge of the pulse to ground. There is no real alternative to something like a gas-gap or a shorted 1/4 wave stub at the operating frequency at the base of the tower and again where the feedlines enter the building. -- Brian Lloyd, WB6RQN/J79BPL 3191 Western Dr. Cameron Park, CA 95682 br...@lloyd.com +1.767.617.1365 (Dominica) +1.931.492.6776 (USA) (+1.931.4.WB6RQN) _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
