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April 9th 04, 09:51 AM

(Hayato) wrote in message . com...
Hello,
I'm building a FM Tx and I'm having some problems to find 100uH RF Chokes here.
So I decide to wind a 100uH air-core inductor, is there any problems on that?
My inductor especifications a
-Wi AWG 24.
-Core diameter: 35 mm.
-Spires: 48, 2 layers of 24 spires each.

You didn't say what frequency the choke will be used for, nor where in
the circuit. But it seems like 100uH is quite a large inductance for
the usual FM frequencies. Winding the choke as two layers will lower
the self-resonant frequency a lot. Even with a very carefully
designed 100uH choke, it will be very difficult to get the
self-resonant frequency up in the 100MHz region. And at 100MHz, 100uH
would give you 62kohms reactance (if you could actually construct it
with high enough self-resonant frequency), which would be more than
you would need in any 100MHz circuit I can think of. If it's a
low-impedance solid state circuit, 100nH might be enough!

Please tell us more. What current do you need to pass in this choke?
How is it used in the circuit? What frequency will it be used at?

Cheers,
Tom