PEAK AND PEP

[KJ4BAE]

Is there a difference, if so what is it? The reason i ask is some meters need a power sorce to work and some dont.

 

[Beetle]

Is there a difference, if so what is it? The reason i ask is some meters need a power sorce to work and some dont.

"Peak" power applies mainly to power utilities and large generating stations. The output from those stations is quite constant. Viewed on an oscilloscope, you'll see nothing but a constant stream of sine waves, all with the same frequency (say 60 Hz) and the same amplitude (say 120 volts). Once in a while you may see a short "spike" as a switch closes or opens, but that generally won't last longer than a small fraction of a cycle.

"PEP" (Peak Envelope Power), on the other hand, is a power measurement system that takes into account the fact that an SSB transmission, modulated by a human voice, is nowhere near a constant amplitude OR a constant frequency. It's the PEP meter that requires a source of power in order for it to work properly. The PEP meter has additional active circuitry that samples the signal, analyzes it, processes it, determines just where within the modulation envelope a particular bit of the signal is at a particular instant, and displays the result.

"Peak" power in voice radio transmissions has no meaning, since the signal has no constant level except when there's no modulation.

If you get a meter that does NOT require power (except maybe for the lights), such as many of the MFJ type meters, it may be switchable between "Peak" and "Avg", where "Avg" stands for "average". This kind of meter will do pretty well if you leave it on the "Avg" function. Any resemblance between what it will read on the "Peak" function to any accepted value is purely coincidental.

For comparison, the Bird 43 reads average power. Period. Its maximum error is plus or minus five per cent of full-scale value. If you add the "peak" board and batteries, you now have the Bird 43P. It reads PEP with a maximum error of plus or minus eight per cent FSV.

All the documentation from Bird regarding "Peak" readings comes from the fact that back in the 70s, when the Model 43 was being used by just about everybody who worked with RF, people KNEW the difference between "Peak" and "PEP", and wouldn't misunderstand if someone just called it "peak". However, the FCC specifies CB, ham and most other SSB transmitters in terms of "PEP", and they don't mean "peak". Many old timers will use the term "peak", but you can bet they'll know they're talking about PEP. One syllable instead of three. Saves time, but be sure you're talking about the right property.

 

[King Mudduck]

On a Dosy power meter. Peak will read the power that your radio produces as well as all of the harmonics ( big loud over modulated truck driver sounding radio ) it throws out as well. While on the avg setting it will only read power and not the harmonics hence the reduced amount of forward swing it shows.

Least that's the way it was explained to me.

 

[W5LZ]

King Mudduck,
I'm afraid is was explained to you a little bit incorrectly. A simple watt meter is not frequency sensitive. It can't tell what's supposed to be there from what's not supposed to be there. No difference between 'Avg', 'Peak', or 'Pep' meters in that regard. It can only measure what you put through it, not if what goes through it should be there or not. Wouldn't it be great if they could though? Wouldn't need to get all that 'frequency sensitive' stuff like 'scopes, freq.counters, etc!
- 'Doc