[AMPS] Q:Rf chokes

Peter Chadwick Peter_Chadwick@mitel.com
Thu, 29 Oct 1998 10:52:50 -0000

I have seen some Kw + chokes using ferrite for HF. In that particular case,
there was a lot of playing about to get around resonance problems, and as
Carl said, using the right ferrite - as I remember (it was over 20 years
ago), there were a number of different types of ferrite used to optimise
operation over the HF band. In the end, it was abandoned as too expensive,
and cheaper (because the amps were set to freq and subsequently rarely
changed) to use a conventional choke and pull a few turns in test if there
was a resonance.

As was also mentioned, saturation needs watching as well. 

And the worst parasitics I ever had was from trying to use ferrite beads
instead of a 'conventional' approach. That was on a 2MHz marine radio using
3 6146Bs for a guaranteed 100 watts into a 10 ohm seriesed with 250pF load.
1 watt 47 ohm carbon resistors with 5 turns on them was also 50% cheaper
than beads there as well. All in all, I heavy a deep distrust of ferrite
beads as the absolute cure all 'snake oil' for all applications.


Peter G3RZP

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