In ,
Scott mentions:
Check this page from Amidon Associates. They are a great supplier of
toroids to the ham community!

http://www.amidoncorp.com/aai_ironpowdercores.htm

Looks to me like 25 turns on a T-50-2 core will give about 3 MICRO
Henries according to Amidon's formula...

Whew! thanks!

My assumption that it was 300 yielded some pretty far out number of turns
for air coils, like 72 or something I seem to recall.

Looks more like 7-8 turns on a cylinder 2.5" in diameter? (that seems
awful small to me) If the tickler coil is currently three turns, would I
just leave it at that? Still, it's nice.. small enough I can probably use
the "good wire" for shortwave. :-) (FWIW old microwaves are apparently an
excellent source if copper wire, I'm tempted to use some of it for an
antenna)

If the capacitance in the tank circuit is ~25-400pF, and I use 3uH then
the frequency response will be about: 4.5mhz - 14mhz ? (does that sound
right?)

This must be why the others I'd looked at involve pluggable or tapped coils?

(In general, is there an ideal ratio of capacitance to inductance for a given
range? IE: could I just add parallel capacitance to lower the frequency
or is it better to increase the coil or.. both? I notice as I run through
some calculations, I need a LOT more uH to cover a smaller and smaller range
of frequencies the lower I get.

He states on his page that it picks up MW, (which is actually what I'm mostly
interested in) but.. didn't mention anything about mixed coils.

His circuit involves a "front end RF amp" (for a total of two coils) when
using air, do I need to some how shield this second coil? I'm assuming it
if it's perpendicular to the main one, thats enough?)

Was hoping to avoid a large air coil because as it is now, the everything
except the capacitors (and AF stuff) fit in a tunafish can for shielding. :-/

Still, the whole point is to assemble it from garbage. I might splurge and
get some mechanical stuff for the tuner, but.. have to get it working first!
(sure am glad I kept that signal injector, it's been really handy for this!)

Jamie
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