look for an old article called "beer can baluns ", in QST, maybe also,in
some of their handbooks. consider, that you need a 1/4 wave length lonf
piece of 25 ohm coax (if you build with no dielectric, will be true 1/4 wave
length, no velocity factor) this will be a "sleeve, or "choke" balun (to
acheive a balanced feed, and will provide you a match under 1.6 to 1!
(assuming your impedence formulai is correct! Math is for your balun Zo
(line required) = Zo (in), Times Zo (out), and then take the SQUARE ROOT
RESULTS OF IT! , (and with the small reactive component, should be
insignificant to the calculation) Good Luck-- Jim NN7K



"Phil" wrote in message
...
Try a T match. The ARRL antenna hand book shows dimensions under the
section
on K1FO Yagis.

Phil, KB2HQ

"MikeN" wrote in message
...
Hi all.

I've got a 70 cm Yagi which is to be matched to a 50ohm feedline,
feeding a 70cm repeater (5MHz split).

The Yagi has an impedance of 12.7+j0.8 (so 4NEC2 tells me).

What are appropriate matching systems to give me the best matching so
that the Tx-Rx duplexer peforms up to its bandpass and notch
specifications.

Thanks

MikeN