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[AMPS] Re: Input Impedance.

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Subject: [AMPS] Re: Input Impedance.
From: (Rich Measures)
Date: Tue, 24 Mar 98 06:57:40 -0800
>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.
?  well said, Phil.  .  Murphy was right.  Things are usually more complicated 
than they look.  
>Phil, K5PC
>"To do is to be".....Sartre
>"To be is to do".....Aristotle
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R. L. Measures, 805-386-3734, AG6K   

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