Posted by
Geoffrey Mackenzie-Kennedy on
Nov 15, 2007; 9:11pm
URL: http://elecraft.85.s1.nabble.com/K2-s-n-4276-Output-Power-Instability-tp366380p366387.html
On Thursday, November 15, 2007 at 7:00 PM, Goody K3NG wrote:
> Using any balun with an unbalanced tuner to feed balanced line can be bad
> news (your mileage may vary, standard disclaimers apply). Under highly
> reactive loads, a balun used like this can become quite lossy. There's a
> couple articles in publications and on the Internet on this, but Cebik's
> article is one that comes to mind (
>
http://www.cebik.com/link/l-bal.html ). It's better to run a real
> balanced tuner like a Johnson Matchbox, the MFJ Balanced Line tuner, or
> others, if you can.
---------------------------------------------------------
Well put Sir!
As a comment to the List, the usual type of cored current balun presented
with a reactive load might appear not to be introducing loss because QSOs
can be made, but as the members of our QRP fraternity well know contacts
both 'local' and DX can be made using very low power given the right
propagation conditions. Proof of this loss can be had by increasing Tx power
up to the power rating of the balun at which point the balun could well
explode if it has not already at a lower power, it will certainly becomes
hot to touch. As K3NG says your mileage might vary because the antenna's
feedpoint impedance as transformed by your feeder and seen by the balun
might by happy fluke be non-reactive, feeder length and feeder impedance are
factors, leaving only the R to deal with. If R turns out to be 200 ohms,
then a 1:4 balun would work well with a Tx which wants to see a load of 50
+j0.
FWIW I agree with K3NG that the classic balanced tuner such as used in the
Matchbox is the best system to use when feeding a balanced line, good
efficiency and versatile.
73,
Geoff
GM4ESD
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