In , Swan Radioman
wrote:

snip
Frank;
Statistical studies of the distribution of signals on the air
versus the signal strength shows that the probability of successful
communication will be the same if the SSB power is equal to one-half
the power of one of the two AM sidebands.

That's exactly what I said.

Your 100 watt figure is
pretty close to what the studies show.

Whats the Peak Envelope Power of a Legal AM radio?

Where did I say anything about PEP? I know what you are trolling for (if you're
not trolling then somebody else will), and yes, the PEP of a 4 watt AM carrier
that is 100% modulated is 16 watts. But that number is misleading because you
are forgetting that an AM signal has a lot of excess baggage. This is one
instance where less is more....

PEP is used when determining the maximum power handling capability of the final
(output) amplifier. In other words, if the AM carrier is going to be 4 watts,
the final must be capable of providing 16 watts. It means nearly the same with
SSB, because the PEP rating of the output amplifier is the peak power level at
which the signal will begin to distort, and since the peak-to-average modulation
ratio is about 3 to 1, a transmitter capable of 12 watts should safely handle
about 4 watts average power in SSB.

But if a transmitter is capable of 16 watts, it seems foolish to use AM with
it's 1 watt sidebands when you can transmit SSB with an effective power of
almost 200 watts AM or better, depending on your average modulation. The FCC
limits the radios to 12 watts PEP, but that's still much better than 16 watts
PEP in AM. In other words, PEP does not represent "talk-power".

For those who don't already know, Peak Envelope Power (PEP) is the RF power at
the brief instant an audio cycle peaks the modulation. PEP is used to describe
SSB power because the standard wattmeter can't measure the average power of an
SSB signal. For example, if your radio is capable of 12 watts PEP, your average
power will be somewhere around 4 watts, but you won't be able to tell because
your wattmeter will be bouncing around with your modulation. So SSB is measured
with a 'peak' value (PEP) instead of a 'real' value (RMS). So even though the
needle is bouncing around, you just need to keep it below the maximum PEP rating
of the radio.

OTOH, AM power is measured in RMS (true) watts, and is a measurement of carrier
power only. The modulation is detected (demodulated) and measured seperately as
a percentage. Modulation -must- be measured seperate from the carrier because
carrier power should remain steady while under modulation; and modulation is
read directly so the operator doesn't have to perform carrier subtractions and
square-root calculations on a PEP reading in order to find the modulation
percentage. Of course you can always add a PEP meter if you really want, but
what's the point of making things difficult and expensive when you already have
all the information you need?

Why is 12 watts the limit for a legal SSB radio?

Because the FCC says so.






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