Posted by
vk4tux on
Apr 05, 2012; 9:15pm
URL: http://elecraft.85.s1.nabble.com/K3-power-reduction-due-to-high-SWR-tp7439053p7441463.html
The external balun you are using is probably better than the one built into
the tuner. An English ham did research some time back and found using a 1:1
current balun less lossy that a 4:1 or others, despite the line mismatch the
tuner made up for it with tested less total loss.
With a well designed tuner/balun combo the circulating current is much less,
and it is only the resistance component that provides loss, not inductive
nor capacitive.
vk4tux
-----Original Message-----
From:
[hidden email]
[mailto:
[hidden email]] On Behalf Of Matt Murphy
Sent: Friday, 6 April 2012 5:53 AM
To:
[hidden email]
Cc: Vic K2VCO;
[hidden email]
Subject: Re: [Elecraft] K3 power reduction due to high SWR
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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