Posted by
Jim Brown-10 on
Aug 06, 2004; 5:28pm
URL: http://elecraft.85.s1.nabble.com/Performance-of-baluns-tp455789p455791.html
On Fri, 6 Aug 2004 16:47:57 +0100, Geoffrey Mackenzie-Kennedy wrote:
>Have noticed over the recent years that current baluns are used in places
> where the load/source Z is not purely resistive (OK will allow a little reactance) ,
>example - an incoming transmission line that looks like R +j (quite a lot) goes
>to a balun then the to an ATU then to the TX.
There are some detailed discussions about baluns and their use on W8JI's
website. Do a google search. Tom makes the point that it is the common mode
impedance of the transmission line that must form a voltage divider with the choke
balun, and that if that impedance is too high (as it would be when it is close to an
odd multiple of quarter wavelengths), the balun must be a very high impedance to
be effective.
DX Engineering sells a nice selection of W8JI-designed baluns. I have several
models and have opened some of them up to look at them (the ones that I can
take apart with screws). These are the best commercial baluns I have seen, and
nothing else is close. One of their characteristics is that the ferrites they use are
"beefy" enough to provide that higher impedance (and to provide a higher power
rating without saturation or overheating).
Jim Brown K9YC
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