Most of the electrical length of these physically-short whips is in the loading coal. Adjusting the length of the 40m whip as you describe would only move the resonance point around within the 40m band. To move the resonance point between bands, you'd need to tap the coil. MFJ makes such a whip; scroll to page 2 of this doc and read about the 1899T:
http://www.mfjenterprises.com/support.php?productid=MFJ-1810T On Thu, Mar 24, 2016 at 6:55 AM John Pitz <crustac...@brig-elec.com> wrote: > Hello All, > > Please excuse the amateurishness of this question, but could you get one > of these whips for a low band such as 40M and use it on say 20M if you > don't extend it fully? > > John Pitz > KD8CIV > > > > On Wed, 2016-03-23 at 22:02 -0700, Wayne Burdick wrote: > > > "Walter Underwood wun...@wunderwood.org [KX3]" < > kx3-nore...@yahoogroups.com> wrote: > > > > > I got the whip for 17m. I figure there is not much difference between > a coil at the base of the whip and a coil inside the ATU. Neither one will > radiate. So get a whip for the highest band you want to use and let the ATU > provide loading for lower bands. > > > > That is not my experience. A high-Q loading coil, combined with the > whip, is resonant near a given band and provides much lower loss than a > whip of the same length with no coil, matched using the internal ATU. So > while the ATU *can* match the whip on bands other than the design band, the > farther you get from the design band, the greater the loss. > > > > That said, a 17-meter whip is a good choice if you want to occasionally > use it on 20 and 15 meters and you're willing to accept the comopromise. > I'll try to put some numbers this. I have whips for all three bands for > comparison. > > > > When I operate mobile I use a 17-meter whip for this reason. A mobile > whip with a larger tunable coil would work much better outside the design > band, but my XYL (when she's riding in my CRV) prefers the svelte look of > that skinny, single-band radiator :) > > > > Wayne > > N6KR > > > > > > > > > > > > > wunder > > > K6WRU > > > Walter Underwood > > > CM87wj > > > http://observer.wunderwood.org/ (my blog) > > > > > > > > ______________________________________________________________ > > 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 crustac...@brig-elec.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 w0...@w0mbt.net > ______________________________________________________________ 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
