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[AMPS] Re: Input Impedance.

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Subject: [AMPS] Re: Input Impedance.
From: (Phil Clements)
Date: Tue, 24 Mar 1998 01:28:36 -0600
At KE9NA wrote:

>At 10:30 PM 3/23/98 -0600, you wrote:
>>>>Everybody claims this, but I haven't seen it.  The input impedance does 
>>>>NOT vary with input power.  I have the exact same match applying 100 
>>>>watts as I do 5.  My SWR does not change. 

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.


Phil, K5PC

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