[ICOM] AM Modulation Levels vs carrier power.

[Sheldon Daitch]

Assume that we are talking about negative modulation here on the numbers,
because in the stateside broadcast band, positive moudlation peaks above
100% are permitted.

But moving on to the contention of carrier power vs modulation level, our
policy on the IBB transmitters is high levels of modulation with lower
carrier
power levels.  That is, if we have to reduce peak power on the transmitter
because of antenna problems, specifically arcing on modulation peaks,
we reduce carrier power, maintaining the modulation levels, to the point
where we reduce or eliminate the arcing problems.  I realize this is
slightly different problem than poor path conditions, but I think the
effect is the same.

George Woodard, who was a director of engineering for RFE/RL,
then IBB and a career with Continental Electronics, wrote a white
paper on the issue, for our system some years back.  I'll have to
dig it up (I could not find it in a quick Google search) and verify
that he wrote what I thought he wrote.

Our target audience is generally using AM receivers with simple
carrier derived AGC, so the audio output is going to be a function
of carrier level. that is, a strong carrier with weak modulation will
give less audio at a given receiver audio gain than a lower level
carrier with full modulation.  Audio derived AGC and use of
sideband receivers might change that audio relationship.

73
Sheldon
WA4MZZ




Peter Markavage wrote:

> Actually AM'ers can run more than 375 watts of carrier output as long as
> they decrease the percentage of modulation. Running the percentage of
> modulation at 90% or 80% has little impact to the person on the receiver
> end. You generally want the AM receiver end to capture the
> signal(carrier), so under poor conditions, more carrier at the expense of
> 100% modulation, is desirable. 1500 watts PEP output is your maximum;
> carrier and modulation are your variables; adjust them according to
> conditions.
>
> Pete, wa2cwa