Mike Lord wrote:
> A question for the group. Some time back, ZL1AXB published a circuit for a
> single 813 grounded grid, using a tuned coil input circuit. He referred to
> it as a "bifilar wound coil." I built the amp and it works like a champ.
> /*snip*/ Pat's circuit covered 40 - 10 meters.
> I would like to use this circuit on 80 and 160.
> Is there a formula for winding the coil?
Think of it as a plate tank (parallel resonant circuit) for a RF amplifier
100 Watt stage with the plate tank coil wound with very small copper tubing
with a (or two) wires threaded through it. The resulting inductance and the
accompanying capacitance/s should be quite similar, the coil is tapped in
normal auto-transformer manor. (used backwards)
Shorting some turns (at the end furthest from the low impedance tap) should
change bands just like a regular tank circuit.
Generally a 40 meter coil will have about twice the inductance of a 20 meter
coil and an 80 meter coil will have four times the inductance of a 20 meter
coil.
and so fourth.
--
Ron KA4INM - nothin's quite as sure as change
from "look through my window" - The Mamas & The Papas
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