|[AMRadio] GG 813 Linear in GE Ham News|
w5omr at satx.rr.com
Sun Oct 9 07:44:09 EDT 2005
Donald Chester wrote:
>> This scheme is also taken even further into the cutoff region in
>> CB-land and used to obtain a low level carrier, say 1 watt, while
>> still obtaining 12 watts peak envelope levels at full modulation. A
>> radio or amplifier set up to do this is called a 'modulator', and
>> gets you alot of 'swing' on the old power meter.
> And gets you a lot of splatter and distortion too.
Because, a truely 100% modulated AM carrier doesn't move, on the watt
meter. The output RF current will increase a bit when modulated, but
the actual carrier level doesn't/shouldn't move when modulated.
When modulation levels exceeds 100%, the plate voltage on the final is
reduced to 0 at that momemt. If you exceed 100% (negative peaks to/past
the baseline, while watching the carrier envelope on a scope), then the
audio voltage then adds to the carrier output. One might think that
this is desireable, but remember that spatter and distortion occur the
instant the negative peaks exceed the carrier level.
A standard carrier reading wattt meter (think 'Bird') should not move,
when the carrier is modulated to 100%. A PEP reading wattmeter (it's my
opinion that you can *not* find one that reads accuratly enough) willl
only show that the rig -is- being modulated, but not if it is being
over-modulated, causing distortion and splatter and being rather
un-neighborly to others on near frequencies..
I know I've said this before, and it just needs saying again...
Don Chester/K4KYV was quoted years and years ago in the AM Press
Exchange (AM P/X) as saying:
"Operating your AM Rig without an Oscilliscope, is like driving your car
at night without headlights."
73 = Best Regards,
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