Jim:
I have not been paying attention to this thread until now. What parameters
are you looking for in the choke you are planning to make?
I have a few of the 2.4" type #31 cores and some Teflon coax plus the
equipment to test the reactance and resistance of a choke. Within reason I
would be willing to build and measure one for you before you spend a lot of
money on cores.
If the frequency range you want to cover is 1-30 MHz I suggest you consider
two chokes rather than one. I think it is much easier to build chokes for
1-10 MHz and 10-30 MHz than one choke that will cover the entire range.
Since you are talking common mode chokes with high impedance (preferable
resistance as John suggested) desired on the outside of the coax shield,
using Teflon coax is a simple way to achieve it.
I have experimented with #61 cores making current chokes which work fine for
1-10 MHz using #14 wire in the form of an open wire transmission line {see
Sevick]. Coax works fine also. I have not yet experimented with the #31
cores so would not be adverse to doing a few tests.
Let me know.
Tod, K0TO
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