|[AMRadio] AM Amps|
W7QHO at aol.com
W7QHO at aol.com
Tue Jan 11 02:11:12 EST 2005
In a message dated 1/10/05 9:12:45 PM, w5omr at w5omr.shacknet.nu writes:
> Kinda Sorta. Depends on the quality of the transmitter. If he
> reduces the carrier output power of the Ranger, then the audio
> output power will rise, because there won't be as much final
> current flowing through the secondary of the modulation
> transformer. Depending on the impedance match of the final to
> the modulator through the mod transformer, determins how much
> more audio will be gained (or lost) when power is reduced from
> the exciter.
Hmmm.. Goes without saying that however the carrier level was reduced the
audio level should be concomitantly lowered to prevent over modulation. Easy
to do, just reduce the mic gain control.
> That, and the natural asymetricalness of the
> operators voice. Lowering the output power, more audio, a 3:1 SR
> (Symmetry Ratio), the 25w of carrier could contain as much as
> 200w PEP. In order for the linear to 'cleanly' reproduce the
> audio, it's going to need more than what the plates of a pair of
> 3-500Z's can deliver (*note: I said "Cleanly")
Two hundred watts PEP on a 25 watt carrier comes out to 400% modulation.
Would take some extreme speech processing to achieve this in the positive
direction while limiting modulation to 100% negative at the same time. Far beyond
the asymmetry of "normal" human speech. So, a pair of
3-500Zs running GG and giving, say, 10db gain, with 35 watts of drive would
give 350 watts of carrier out and modulating at 100% with a reasonably
asymmetric audio signal would give 1400 W. PEP. I have been using a 3-1000Z linear
in this way for years with excellent results.
Speaking of the human voice, there undoubtedly exist some levels of asymmetry
depending on the speaker. I suspect, however that much of the asymmetry
observed and reported is actually the product of nonlinearities in speech
amplifier circuitry, particularly in the early, low-level stages.
Dennis D. W7QHO
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