Ferrite-cored chokes (balun) heat up and change apparent swr. David G3UNA/G6CP
> On 15 July 2020 at 17:36 j...@kk9a.com wrote: > > > That is quite an assumption. A 2el 40m beam with large efficient > High-Q loading coils will have less bandwidth than for example one of > the popular US manufactured beams that use 68 turns of small wire in > each coil. The latter is more likely to have heating issues. I have > never noticed any SWR changes or amplifier re-tuning with my 40m > OptiBeams during heavy use. > > John KK9A > > > Jim Miller AB3CV wrote: > > Since it is so narrow I suspect it may be a trapped design or have loading > coils which at 1500w may be heating and detuning as a result. > > 73 > > jim ab3cv > > On Wed, Jul 15, 2020 at 11:45 AM Ray Spreadbury via Elecraft < > elecraft at mailman.qth.net> wrote: > > > > > > > A correspondent asked me why I needed to tune a resonant antenna. > > The reason was because although the Yagi was tuned to resonate at about > > 7.130MHz it unfortunately has a rather narrow bandwidth. I needed to > > operate SSB in this contest in ITU Region 1 SSB, which is between 7.080MHz > > and 7.200MHZ. At 7.080MHz the SWR (with tuner bypassed) was 1.75:1 & at > > 7.200 was 1.95:1. I would be operating at power so I preferred to tune for > > 1.1:1. > > Yes I know the Yagi is not very good with that narrow bandwidth, but it is > > what it is. Normally I operate CW only on 40M & tune it to 7.030 with the > > bandwidth covering the preferred Region 1 CW portion of the band ie7.000 to > > 7.040 and the tuner is not needed. > > 73 Ray G3XLG > > ______________________________________________________________ > 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 d.cut...@ntlworld.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
