[Boatanchors] AM PEP

[Donald Chester]

From: Gary Schafer    garyschafer at largeriver.net
 Fri Oct  2 00:41:31 EDT 2015

> If we get the math right PEP is easier to understand.

> First, there is a difference between peak power and peak envelope power
> (PEP).

> A 375 watt carrier requires 187.5 watts of AVERAGE power to modulate to 100%
> which equals 1500 watts PEP.

I'd venture to guess that's WAY over the heads of many, if not most of to-day's amateur licensees.

The FCC admitted as much in the Report and Order of that infamous proceeding, when they deleted the previous requirement that amateurs running more than 90% of the  legal power limit, must possess measuring instruments capable of ACCURATELY MEASURING transmitter power. They included some nonsense in the text about amateurs being able to determine whether or not their signal is in compliance by using "means other than accurate measurement".


> Per the FCC, The definition of PEP is the AVERAGE POWER contained in 1 cycle
> at the PEAK of the modulation envelope.

That delves back into early arguments over the physical existence of sidebands, which raged in the early 1920s.  Some British engineers had argued that sidebands exist only in the mathematics that describe the modulation process, and that with modulation, the carrier merely increases and decreases in step with the modulation; some other American engineers counter-argued that sidebands indeed exist in physical reality.  As we all know, eventually those arguments were settled and the American engineers' argument won out.

Now, it's a well known fact that the AM signal consists of a carrier, upper sideband and lower sideband, something that can readily be displayed on a spectrum analyser or panadaptor. The amplitude of the steady unvarying carrier can be seen at all times towering well above that of either one of the sidebands. The above definition appears to revert back to the 1920s concept of a carrier on a single frequency varying up and down in amplitude.  How can we have "one cycle" at a specific power level, when the AM signal consists of three independent components, each with its own distinct waveform?

For those who obsess over their "pee-e-pee", in the thirty-some years since  the power limit rule was changed (or should I say mutilated), how many times have you heard of a ham receiving a citation because a few of his voice peaks strayed over the magic number? About the only citations for over-power that have been reported are cases in which the station's power level egregiously surpassed  the legal limit, and most, if not all, of those were with CBers, not  hams, caught running hundreds if not thousands of times more than their legal power, usually after attracting undue attention to themselves by generating widespread interference and disruptions. 

Don k4kyv