[AMRadio] Re: What is PEP?


Bob Macklin macklinbob at msn.com
Fri Feb 15 15:40:16 EST 2008


In the OLD DAYS the rule was 1KW INPUT POWER. But that rule did not work
when SSB became the predominant phone mode.

I think I recall a period where the power limit was defined in terms of DC
INPUT POWER or PEAK ENVELOPE POWER.

In those day the FCC did have a competent FIELD division. And they did have
direction finder trucks. The ones I remember from about 1950 were BREAD
VANS. They did go out and check on hams that were causing problems. Those
were the early days of TV.

Bob Macklin
K5MYJ
Seattle, Wa,
"Real Radios Glow in the Dark"
----- Original Message -----
From: "D. Chester" <k4kyv at charter.net>
To: <amradio at mailman.qth.net>
Sent: Friday, February 15, 2008 12:30 PM
Subject: [AMRadio] Re: What is PEP?


>
>
> > Don,
> >
> >   It seems that we have defined PEP power pretty well:
> >
> >>"Well, PEP is defined as the AVERAGE power over at least one RF cycle at
> >> the most powerful point of the envelope."
> > Now, since we do not speak with sine waves, the average "power point of
> > the envelope" is going to be less than 0.636 (sine wave average) of the
> > peak >value. With many voices the average might be 0.2 to 0.5 of the
peak.
> > Doesn't this mean we can increase the peak power until the PEP as we
have
> > defined >it hits 1500 watts? It seems that many of us confuse peak power
> > with Peak Envelope Power. The definitions are different. If I have this
> > correct, then >unprocessed voice peaks can be increased until the PEP
> > legal limit is achieved, and the carrier level might be a lot more than
> > 375 watts. Maybe the KW1, >or Johnson Desk KW at Hi-Tap are still legal?
>
> Now, this makes me REALLY feel for all the Hammy Hambone types out  there.
> It has ME confused!
>
> BTW, another term for average power is "mean" power.  There is no such
thing
> as "rms" power.  MEAN power is calculated, using Ohm's law, by multiplying
> RMS voltage by RMS current, as they work into a resistive load.
>
> Rms voltage and current are the "effective" values of an alternating
current
> and voltage, meaning the equivalent measurement of DC that would produce
the
> same effect.  With a sine waveform, the rms value is .707 times the peak
> value.  But the mean power into a  load is also dependent on power factor,
> that is, whether the voltage and current are perfectly in phase, as they
> would be into a resistor.  In a.c.circuits with a reactive component,
> voltage and current may not be exactly in phase, so that a direct
> calculation using measured values of voltage and current may give a figure
> that is greater than the actual power.  That's why transformers are rated
in
> volt-amperes, not watts.
>
> We don't talk in p.e.p. but we don't talk in sine waves, either.  The
> loudness and interference-causing capability of a signal over the air is a
> function of mean, or average power radiated from the antenna, regardless
of
> where occasional voice peaks may reach.  The average amplitude of a
typical
> human voice waveform is about 7 to 10 dB below the amplitude of the voice
> peaks.  In other words, unless we use clipping or severe peak limiting,
when
> our voice modulates a  transmitter 100% on peaks, the average percentage
of
> modulation is more like 30%.  If you ever visit a properly running
broadcast
> studio that still uses analogue, electro-mechanical VU meters, you will
> notice the readings stay well over to the left side of the scale most of
the
> time to avoid hitting the red zone on peaks.
>
> Don k4kyv
>
>
>
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