Suppose that I want an inductor of 5 mH that will handle 1500 watts into a
3:1 SWR from 1.8 to 30 Mhz (to build an L network antenna tuner, at the
output of a solid state amplifier, say).
12 turns on a T-400A-2 powdered iron core will give me something like 5.2 uH
at a maximum flux density of 70 gauss at 500 volts at 1.8 Mhz (with no DC
current flowing). 70 gauss is acceptable at 1.8 Mhz (and it gets better
relative to the spec as you get higher in frequency). Fine, I'm a happy
camper.
Now suppose that I want an inductor of .5 mH, all else the same. 4 turns on
the same core gets me .58 mH, close enough - but the flux density is now
210, well beyond acceptable limits. Things get worse for smaller inductors
- the flux density goes through the roof for just 1 or 2 turns.
I can't buy a bigger core easily - so what do I do? Is my only option an
air core inductor (which I then have to shield...)? It seems more likely
that I am being dense, as usual :-)
Thanks!
***dan, K6IF
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