[AMRadio] FCC's AM power


Gary Schafer garyschafer at largeriver.net
Mon Sep 26 18:59:25 EDT 2016


Actually most watt meters that have a "peak power" position are intended to
show PEP and not peak power. Some are better than others at doing so.

Although most watt meters do detect peak power but are calibrated in average
power. Peak envelope power is just a fast responding average power meter.

Here is a wattmeter that is excellent at reading PEP. Yes it will read AM
PEP accurately.
http://www.telepostinc.com/lp100.html Price is around $465.00, not much
different than a Bird and a couple of slugs.

Note that true "peak power" is different than "Peak envelope power (PEP)".
Peak power is measured from the actual peak voltage of the signal where as
PEP is measured from the RMS voltage of the signal which gives us AVERAGE
power (some incorrectly call this RMS power).
With modulation PEP is the average RF power at the crest or peak of the
modulation envelope. Easily seen on a scope.

Peak envelope power and average power of a CW signal are the same. Think of
the CW signal as a steady carrier, you find its power in the usual way and
just call it average power. When keying the CW signal on and off you create
an "envelope" for each character. The power at the crest or peak of this
envelope is the peak envelope power, the same as if you were holding the key
down.
A voice signal creates this same kind of envelope with modulation. The only
difference is the envelope varies up and down and slightly in frequency. For
peak envelope power we are only concerned what the level of the maximum
value of this peak. It is still an average power signal like the CW signal
only varying in strength.

Don't worry about being able to "catch" those illusive modulation peaks of a
transient of some high modulation frequency. There are many RF cycles
contained in any modulation envelope.
For example a 7 MHZ RF signal has 7 million cycles per second. When
modulated by say 7 KHZ modulation signal (probably a higher audio frequency
than most would use) there will be 1000 cycles of RF contained in that one
modulation envelope. 
The peak envelope power measurement is really done at an audio rate as far
as variation of the signal.

73
Gary  K4FMX

> -----Original Message-----
> From: AMRadio [mailto:amradio-bounces at mailman.qth.net] On Behalf Of
> Robert Bethman
> Sent: Monday, September 26, 2016 3:50 PM
> To: amradio at mailman.qth.net
> Subject: Re: [AMRadio] FCC's AM power
> 
> Ollie and All,
> 
> It doesn't matter whether it is an Autek or a Bird Peak reading meter.
> 
> They simply read the Peak Power Output Power.
> 
> I don't know a single watt meter that is capable of reading Peak
> Envelope Power.
> 
> There is far too much circuitry involved in reading PEP.  WE as a group
> of Amateurs don't have that sort of budget!
> 
> I suspect an oscilloscope of beyond normal calibrated one would do so
> either.
> 
> Even a darn good Tektronix Oscilloscope would be rather useless in an
> attempt to read PEP.
> 
> Regards, Bob N0DGN
> 
> -----Original Message-----
> From: AMRadio [mailto:amradio-bounces at mailman.qth.net] On Behalf Of
> Oliver Steiner
> Sent: Monday, September 26, 2016 4:19 PM
> To: Geoff <ars.w5omr at gmail.com>
> Cc: amradio at mailman.qth.net
> Subject: Re: [AMRadio] FCC's AM power
> 
> I'm not clear about the distinction between "peak power" and "peak
> envelope power" (If there is one).  My Autek power/swr meter lets me
> select between average power and peak power, but am I monitoring peak
> *envelope* power when I have it switched to the "peak power" position?
>    --- or is peak envelope power only possible to determine with a
> calibrated oscilloscope?
> 
> I'm grateful to read your answers to this.
> 
> Ollie
> W2QXR
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