"Tom Bruhns" wrote in message
m...
I've made coiled-coax choke baluns at 440MHz. Seems to work fine.
Generally expect to use pretty small line, to be able to make a small
enough coil. The self-resonance is nice but not critical. You're
just looking for a moderately high impedance. I have a program that
does a good job of estimating the self-resonant frequencies of coils,
but it's not on this machine so I can't check for you...I think one of
Reg Edward's programs also estimates self resonance for coils. If you
can get an impedance that's a few times the load impedance, you should
be OK. In feeding an antenna, it may be as important to use a couple
such chokes, spaced about a quarter wave apart, to keep the antenna
from coupling strongly to a possibly resonant section of feedline.

Cheers,
Tom


Thanks for that info, Tom.

If resonance is not necessary, then I need only one turn of .75 diameter to
make sure resonance is higher than my operating frequency. That would make
the coil with parasitic capacitance look inductive.

73,
John