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[AMPS] Re: Input Impedance.

To: <>
Subject: [AMPS] Re: Input Impedance.
From: (Pete Smith)
Date: Tue, 24 Mar 1998 20:45:00
At 06:57 AM 3/24/98 -0800, Phil wrote (I think - these multi-layer quotes
are confusing): 

>>Your SWR does not change enough to see it because as you lower the input
>>power, you also lower the cathode current, maintaining about the same
>>input impedance. Try this...tune up your amp and apply 100 watts drive.
>>Note the cathode current. Reduce the drive to 50 watts. The cathode current
>>should be close to 1/2 what it was at 100 watts input. Since input impedance
>>equals drive power divided by peak cathode current squared, you can see how
>>the input impedance stays fairly close throughout the operating range. The
>>low Q of the tuned input L/C allows compensation for any variations in the
>>drive/cathode current ratio.

I don't know the theory, but on my SB-220, when I run it on 24 MHz I
usually use the autotuner on my TS-930 to match the input network.  As I
tune the final, the autotuner senses a change in the input SWR (I can see
it on the 930's SWR meter as well) and responds by retuning.  So both it
*and* I are seeing the change.

73, Pete Smith N4ZR 

"That's WEST Virginia.  Thanks and 73"

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