Chris wrote:


To reduce the drive power to an amplifier and make the modulation louder.

Chris

I see. But reducing the carrier won't make the modulation louder, only
more distorted.

Well, let me back up a little. What I said is true if the modulation is
100%.

But let's suppose that the transmitter is capable of only 50%
modulation. In that case, you *can* make the modulation louder by
increasing the amount of audio applied to the carrier. If the
transmitter is fundamentally designed to handle 100% modulation, this
would require only more audio gain or a "hotter" microphone. That would
be the best way to make your modulation louder.

But let's say that instead, you reduce the carrier from 4 watts to 1.
Then the 1 watt carrier would be 100% modulated. (100% modulation of a 4
watt carrier takes 2 watts. 50% modulation takes only 1/2 watt, which
will modulate a 1 watt carrier 100%.) Now you have 100% modulation of
the 1 watt carrier. There's the same amount of transmitted audio power
as before -- 1/2 watt --, so you're really not making the audio any
stronger, and no one will be able to copy you any better than before.
(In fact, your weaker signal will have more trouble getting through in
the presence of noise or interference.) But if you're the only signal
being heard, the receiver's AGC (automatic gain control) will react to
your weaker carrier by turning up the receiver's gain, making the audio
sound louder. The person receiving your signal can make your audio just
as loud with a 4 watt carrier by manually turning up the volume.

So I'll relent and say that reducing the carrier might make your audio
sound louder -- but only if your transmitter is undermodulated in the
first place, there's no stronger signal to control the receiver AGC, and
if you don't reduce the carrier so much that it makes the modulation
exceed 100%. But your ability to get through interference and noise will
probably be reduced.

Roy Lewallen, W7EL