On 23-May-10 1:10 PM, Joe Subich, W4TV wrote:
> The average ham has even less ability to accurately measure the
> 1 dB compression point on an amplifier than he has of accurately
> measuring IMD. Most don't have one accurate wattmeters much less
> two ... nor the ability to understand the issues of exciter foldback
> and the changes in SWR between the exciter and amplifier with tuning.
The beauty of 1 dB compression power is that unlike two tone testing,
absolute accuracy is not required to achieve proper operation of the
amp. All that is required is some linear response indication of output
power and input power. You can even make the required measurement with a
peak detector and a DC voltmeter and get exactly the same results. Of
course this assumes you know what a dB is and how it relates to volts,
amps, and ohms, and what all those funny little buttons on your
calculator do. You DO NOT need to know what the actual power output is,
you only need to know at what point you should be adjusting the drive to
when running a linear mode.
The exciter doesn't enter into the test at all other than supplying a
carrier. It can be a class C exciter for all that matters. It has no
effect at all on the outcome of the measurement of the amplifier.
No fancy test equipment required, easy to do, and essentially free
(other than the time it takes to learn how) such a deal. The down side
is that your nifty peak reading watt meter wil ALWAYS wind up reading
less power than it did when you were slamming the crap out of the tubes
and splattering the whole band. Can't have everything I guess...
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