On Sat, 1 Mar 1997 13:42:13 -0500 bruce muscolino <w6toy@pop.erols.com>
writes:
>At 07:59 PM 2/27/97 EST, you wrote:
>>
>>I get RF peak voltages of about 45v (90v peak to peak) across my 50
>>ohm dummy load, resulting in V*V/(2*50) or 20.25w. With the variable
>>output power modification, (ac coupling the MOSFET gate and varying
>> the gate bias voltage as derived from the "T-" signal from 0 to about
>> 5.25v), I can get continuously variable power from 10mw (1v peak) to
>>20.25w (45v peak).
>>
>You ought to clarify that V you used in your calculation is multiplied
>by .707 to get rms. Power is an average quantity, not a peak one. Oh,
>yes, I did check your math.
>
Ah, keeping me honest!
Yeah, I didn't want to get into all of that. Yes, the factor of two
takes care of the RMS to average involving V*V, as you have noticed.
Actually, I noticed that a stock 38 special with the stock 5w mod will
not work as I first said. The bias for the gate for that modification is
derived from the 12v line. As the rig input voltage is raised, the bias
voltage to the IRF510 goes up also, which messes things up by biasing the
IRF511 to high. In fact I think this caused problems with folks early on
who tried to run 13.8v.
I derived my gate bias from the "T-" signal which is regulated, of sorts,
to about 7.75v, so I had no problems. People that have used the direct
coupling between the gate of the IRF510 and the driver, shorting out the
coupling cap will be ok also.
Now to see if I can get the 40m mods to my 38 special all wrapped up by
tonight and get it out on the air!
- Dan Tayloe, N7VE, Phoenix, Az, QRPL # 696, Az ScQRPions
>
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