[ARC5] ARC-5 TX output circuit modeling [long]

[W7QHO at aol.com]

In a message dated 1/7/07 1:48:19 PM, ianmwilson at earthlink.net writes:


> The large capacitor goes across the 50 ohm load. The parallel combination 
> of 50 ohms and 1000pF is equivalent to about 9 ohms in series with 1200pF.
> 

All,

OK, made some quick and dirty tests with my GP-7 on 40M. The GP-7 "F" tuning 
unit includes a plate tank coil with a rotatable link feeding a roller 
inductor the same as in the command sets, but I don't know at this point just how 
many turns are on the link or what the link-to-tank turns ratio might be.

With 300 watts input to the 803 PA I get 210 watts out into a 50 ohm dummy 
load with a single 50pf series   capacitor, the roller inductor adjusted for 
maximum loading and the link engaged at approximately 25%.   Current through the 
roller iinductor under these condx is 2 amps.   Adding 1000pf across the 50 
ohm load resulted in the output dropping to 170 watts and the inductor current 
rising 50% to 3 amps.   Same input to the PA, of course, and in both cases the 
link engagement remained at approx. 25%.   Inductor and PA tuning settings 
also changed as expected.

Higher current through the link and the inductor accounts for the 40W loss 
maybe?   

Dennis D. W7QHO
Glendale, CA