[AMPS] Smallest practical 1.5KW 20uH coil

[Radio WC6W]

Hello to the group,
  I'm contemplating some alternative designs for a 20uH,160M "padder",
coil, to be switched in following the Pi-net roller coil in my 4-400A amp
under construction.

  The "typical" 3" long by 3" diameter section of B&W stock, including
reasonable clearance to adjacent components, would take up a bit too much
space in this instance.

  I thought of winding 20 turns of #10 teflon on four stacked
(Micrometals / Amidon) T200-2 iron powder toroids but, that also gets to
be rather large (2.25" diameter by 2.5" long) and is surprisingly lossy,
if I did the math correctly.  

  I'm now considering a short solenoid cross section wound in the form of
two adjacent spirals (one spiraling into the center, the other out)
fabricated from .375 by .07 silver plated copper ribbon.   Sixteen turns,
8 in each spiral, in a 3" diameter by just under 1" thick form factor
should provide the requisite inductance.  I'll just slip some thin strips
of fiberglass between the turns to keep them properly spaced.  The only
drawback that I perceive in employing this geometry is the somewhat
higher than usual inter-turn capacitance but, this part is only for use
on 160M.

 Comments, suggestions, alternative ideas???  but, please no
superconductors! :-)

73,
  Marv WC6W











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