Posted by
Don Wilhelm-4 on
Dec 09, 2011; 1:11am
URL: http://elecraft.85.s1.nabble.com/KAT500-update-tp7072932p7076577.html
Ron,
Yes, that is valid justification for putting the balun at the tuner
input, BUT it ignores the physics of the tuner itself. If the tuner is
actually a balanced design, I have no problem, but many try to force fit
an unbalanced tuner design after the balun. That latter part is the
part that does not fit. There is no way that an unbalanced network no
matter how well isolated can preserve the balance - just consider the
phase of the signal as it passes through each tuner element if you want
proof.
If you want to use a balun at the tuner input, then please follow it
with a balanced tuner t maintain that balance.
If you want to use the "rule of thumb" that the balun impedance should
be 10 times the load impedance, then refer to K9AY's RFI and balun
information and use those 5 or 6 large cores to provide the proper
choking impedance for up to 500 ohms antenna impedance (5000 ohms
impedance for the balun).
73,
Don W3FPR
On 12/8/2011 7:36 PM, Ron D'Eau Claire wrote:
> Is it true that the efficiency of a balun is not affected by the impedance
> of the line in which it is used?
>
> The justification I had seen for putting the balun at the tuner input where
> it will see a load very close to 50 ohms resistive (when the tuner is
> adjusted for a "match") while at the output the balun may see anything over
> a huge range of impedances.
>
> Ron AC7AC
>
>
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