Bob Miller wrote:

On Thu, 02 Mar 2006 14:00:41 GMT, David wrote:

On Thu, 02 Mar 2006 13:39:00 GMT, Bob Miller
wrote:

On Thu, 02 Mar 2006 00:28:43 GMT, Telamon
wrote:


I guess I'm missing something here. If the impedance of a 1/2 wave
dipole at its resonant frequency is about 72 ohms, and at twice that
frequency is about 5000 ohms, how is any single balun going to work
for a multi-frequency listening or transmitting setup? How does the
popular 9-1 balun used by so many swl-ers work for multi frequency
listening? Would it be to simply get the impedance within yelling
distance of the receiver input, or is it really needed at all, given
the pretty good sensitivity of most modern receivers?

Who uses 1/2 wave dipoles for receive only?

9:1 baluns are for random wire monopoles.

The purpose of the dingus is to more properly mate the random wire
with the shielded transmission line. It keeps noise pickup down and
bleeds static electricity away from the receiver.

Thanks for clarifying, but the question remains the same. Why would a
random length wire monopole at assorted listening frequencies always
be at nine times the impedance of the coax feed? If it is not, why the
fixed 9 to 1 ratio of the balun? Would not a variable device, such as
an L-circuit antenna tuner work better?

Of course it would, but that involves a lot of fiddling everytime one makes a
big frequency change whilst the balun approach offers a good compromise in
evening out the impedence mismatch, without the hassle.

http://members.aol.com/DXerCapeCod/z_transformers.pdf

http://www.dxing.info/equipment/impe...ing_bryant.pdf

dxAce
Michigan
USA