[TowerTalk] resonance/swr/impedance plots

[Bill Turner]

On Sat, 2 Dec 2000 02:42:23 EST, K7GCO@aol.com wrote:

>Mount a BC 3 gang variable (50 cents in a flea market) in a box with it in 
>series with the center lead and connect to the mobile feedpoint.  Insulate 
>the shaft coming out of the box. 
__________________________________________________________

This works after a fashion, but whatever capacitive reactance you add
for tuning purposes must be also be added to the coil for a net zero.
This increases losses in the coil to some extent.  I prefer to use a
roller inductor in series with the antenna.  I set it to zero
inductance, resonate the antenna at 3999 kHz and then roll in
additional inductance as needed for lower frequencies.  I have a
reversible DC motor with gear reduction to do it and it works like a
charm.

With this method, you don't have any more inductance in the coil than
is absolutely necessary.

73, Bill W7TI

--
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com