[Elecraft] KPA1500 in the IARU Contest Last weekend

[CUTTER DAVID]

Ferrite-cored chokes (balun) heat up and change apparent swr.  

David G3UNA/G6CP

> On 15 July 2020 at 17:36 john at 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
> 
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