I am thinking that if you make the wire more than 1/4 wavelength at the lowest frequency, all you would need to tune it would be a variable capacitor.
Vic 4X6GP > On 16 Jul 2016, at 20:39, Ron D'Eau Claire <r...@cobi.biz> wrote: > > 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 k2vco....@gmail.com ______________________________________________________________ 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
