One approach to reduce "RF in the shack" using an end-fed wire is to resonate the "counterpoise" for the band you are using. MFJ made just such a "tuner" (model 931 IIRC) but any tunable L-network will work. The idea is to adjust the "tuner" for maximum current flowing into the counterpoise (meaning the counterpoise is offering the lowest possible impedance to the equipment it is connected to.) I have successfully used that in a 2nd story apartment feeding an end-fed wire running outside. I know one Ham who bought the MFJ box and found it worked FB.
For a homebrew "counterpoise tuner" you'll need an RF ammeter but a good cheap one is an incandescent flashlight bulb in series where the counterpoise connects to the rig chassis. Tune for the counterpoise for maximum brightness with the rig running at the lowest power that will light the bulb, then short-circuit the bulb for higher power. Of course, the adjustments will interact with the tuner settings for the end-fed wire. But the "tuning" of the counterpoise is usually broad enough (low-Q) that noting the settings for each band you can return to them without doing the whole retuning thing again. (The MFJ box my buddy bought has an ammeter built in.) My "counterpoise" was a thin white wire run around the baseboard of the shack and down the hall - about 30 feet total. White wire + apartment white wall = invisible counterpoise. Worked FB 40 through 10 meters. While that will reduce the RF voltage on the rig itself, you will be sitting in a high-level RF field from the end fed wire, which limits your maximum power to meet radiation exposure limits, depending upon how far from you the antenna is located and the band you are using. 73, Ron AC7AC -----Original Message----- From: Elecraft [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Drew AF2Z Sent: Saturday, July 16, 2016 9:30 AM To: elecraft@mailman.qth.net Subject: Re: [Elecraft] Power Supplies I do have counterpoises: "decent" is another matter. If I had better shack/antenna choices I wouldn't be using an endfed wire to begin with. So, the counterpoises, ferrites, ground loop isolators, equipment/cable arrangement are all part of the solution. 73, Drew AF2Z On 07/16/16 12:04, Jim Brown wrote: > Drew, > > Forget your field strength meter and 1) concentrate on providing a > decent counterpoise for your antenna so that return current flows on > that counterpoise rather than ground wiring inside your shack; and 2) > on killing Pin One Problems in the equipment in your shack. You have > high field strength in your shack because the antenna ends at your > shack, and because it is working! > > Study k9yc.com/RFI-Ham.pdf > > 73, Jim K9YC > > On Sat,7/16/2016 8:26 AM, Drew AF2Z wrote: >> I have an endfed wire antenna for the low bands so there is RF in the >> shack which needs to be managed. In such a case a field strength >> meter is handy in figuring out how to arrange equipment, cables, >> keyboards, etc and placing ferrite toroids and snap-ons for best >> results. I use an old Simpson 37 > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to r...@cobi.biz ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
