On Sat, 22 May 2010 14:28:54 +0100, Steve Hunt wrote:
>It all seems pretty academic when I could shift the SRF by similar
>amounts simply by changing the way the leads were dressed. As Ian said
>earlier, a choke which achieves high resistive impedances is the only
>way of ensuring a robust and repeatable design.
YES. And that is exactly why the #61 material is a very bad choice -- a
high resistive impedance can be achieved for a relatively small frequency
range. For most of the spectrum it is either inductive or capacitive, and
can be cancelled by the common mode reactance of the transmission line.
The #43 material achieves this above 5 MHz, and the #31 material achieves
this from the AM broadcast band up to VHF.
Another way of looking this is that chokes wound with #61 have Qs on the
order of 10, while HF chokes wound with #31 or #43 have Qs less than 0.5.
73,
Jim Brown K9YC
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