[AMPS] Inductors

[ToddRoberts2001@aol.com (ToddRoberts2001@aol.com)]

I think the most efficient variable inductor I have seen is one based on the 
"screwdriver" antenna. A coil is placed inside a copper tube of slightly 
larger diameter. At one end of the copper tube is a ring of heavy-duty finger 
stock that contacts one turn of the coil. As one end of the coil is rotated 
on a threaded shaft the other end of the coil emerges from the copper tube. 
The turns inside the copper tube are completely out of circuit as RF flows on 
the outside of the copper tube. This eliminates the lossy "shorted turn" 
effect that is present on standard roller inductors. I am waiting for someone 
to apply this technique to high-power transmitting inductors  for amplifier 
use. 73 Todd Roberts WD4NGG .

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