Re: K3 power reduction due to high SWR

Posted by Matt Murphy on Apr 05, 2012; 7:52pm
URL: http://elecraft.85.s1.nabble.com/K3-power-reduction-due-to-high-SWR-tp7439053p7441241.html

One related question, when speaking of the efficiency of a balanced
feedline + balun and tuner, what would be a best/worst case scenario for
the loss introduced by the balun+tuner?  Would loss vary significantly by
frequency for a nonresonant antenna?  I'm trying to develop an intuition
about the lossiness of the tuner+balun compared to, say, 50' of RG213.

I've opted to use a 1:1 balun at the end of 450 ohm ladder line, then a
short length of coax into a TenTec 229 tuner.  In the informal test that I
performed, the homebrew 1:1 balun + coax jumper improved the performance of
the antenna compared with connecting it directly to the balanced line
connectors on the back of the tuner.

73,
Matt NQ6N



On Thu, Apr 5, 2012 at 12:23 PM, Don Wilhelm <[hidden email]> wrote:

> Vic,
>
> Where was the frequency of the GDO with respect to the band the tuner
> was set to?  If it was below the band of interest, I would expect
> something like that - the T-Network is a high pass filter.
>
> 73,
> Don W3FPR
>
>
> On 4/5/2012 12:28 PM, Vic K2VCO wrote:
> > Speaking of balanced lines and tuners, I recently did an experiment that
> surprised me.
> >
> > I have a dipole fed with 600-ohm open-wire line (and some window line
> indoors). I usually
> > tune it with a Johnson Matchbox, a fully balanced link-coupled tuner.
> >
> > I was lucky enough to get my hands on a massive, high-quality edge-wound
> rotary inductor
> > in a well-made aluminum enclosure. So I built a high-power T-network
> tuner with it. I
> > purchased a good (and expensive) 1:1 balun designed for use after a
> tuner from DX
> > Engineering, and compared the T-net + balun to the Matchbox. I didn't
> notice any
> > difference in the strength of received signals between the tuners.
> >
> > But here is the surprising part: I expected that the Matchbox would
> provide better
> > balance, which would reduce radiation and pickup from the feedline. To
> test this, I
> > coupled a grid-dip oscillator to the feedline about 20 feet from the
> tuner.
> >
> > To my great surprise, the signal from the oscillator was much weaker
> with the T-network +
> > balun than with the Matchbox!
> >
> > Signals the same, 'noise' weaker. So much for the need for 'truly
> balanced' tuners!
> >
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