PRETTY COOL READ ON (PEP)

[TonyV225]

This was kind of cool when I read it and I thought I post it here. We have had this discussion on 75 meters a few times they say theres a formula of taking your power off a standard meter without a true peak reading and multiply it to 3.14 and its supposed to be close although this seems to be kind of out of sorts to me.

I take for example 300 watts which 300 x 3.14 = 942 uum Im thinking Im not doing this right has anyone ever heard of this formula to calculate this?? here is the article that I found. Its a good read but it doesnt give me the formula for calculating Average to PEP like the boys were telling me on 75 meters.

Measuring SSB transmitter power

 

[Captain Kilowatt]

That's the thing about the internet,there is soo much usefull information available it boggles your mind. The bad thing is that it is offset by an equal amount of BS and you are left to figure out which is which.

 

[Lazybones1222]

That's the thing about the internet,there is soo much usefull information available it boggles your mind. The bad thing is that it is offset by an equal amount of BS and you are left to figure out which is which.

yep - what he said. Plus - hams will argue about anything. Put three and a room, and it seems there will always be at least two opposite schools of thought on any given subject.

 

[W5LZ]

TonyV225,
VK1OD's testing method is flawed for several reasons. One of those reasons is that a mechanical meter can not follow the peaks of a non-constant signal, it just isn't fast enough. There is no 'set' figure for 'normalizing' such a characteristic of a mechanical meter, no two mechanical meters are ever the same.

Instead of using '3.14' for your calculations, try '1.414' instead (or the other way around, use '.707'). That '1.414' is used to convert RMS to Pep, '.707' for converting Pep to RMS. Deals with the amount of 'work' done with AC. 'Work' = 'power'.

None of this is ever going to be accurate to more than maybe 1 or 2 decimal places, just too many 'error' variables involved.

And probably most important, if you try checking power output with something other than a sinusoidal test signal, you have a much better chance of winning the lottery than finding a correct answer. Will that mean a really 'correct' figure? No, but it's ball-park close, which is close enough.

When dealing with people and opinions, multiply the number of people by 2, add in 1/2 the number of people to that figure, and you come up with the -minimum- number of opinions possible.
- 'Doc


None of the above takes efficiency into account!

All of this can be misconstrued to make it come out, or mean whatever you want it too.

 

[HiDef]

VK1OD is a sharp cookie. Nowhere does he say to rely on a mechanical meter for accurate measurement other than the quote below. What he does say is to use a peak hold circuit for peak power readings. He also said:

<These instruments are calibrated on a steady (unmodulated) carrier, and are only accurate on such a waveform.>

 

[HiDef]

A simple formula cannot be used to convert between P.E.P. and average values on complex waveforms such as voice ssb.

 

[W5LZ]

HiDef,
"A simple formula cannot be used to convert between P.E.P. and average values on complex waveforms such as voice ssb." --
I know. So using voice as the audio signal source is kind'a silly, isn't it! So don't use a complex wave form (voice), use a 'simple' wave form for testing instead.
And just for grins. Those formulas are accurate for any instantaneous time period reading in any kind of wave form. Seems like if you wanted the 'average' power figure you'd use an 'averaging'/RMS meter (Bird 43??), wouldn't you say? Oops! Better not do that, then you'd end up with them 'Bird watts', right?
(Measure a carrier signal on both an RMS and Pep meter. If they aren't the same reading, better check that Pep meter, it ain't right.)
- 'Doc

 

[HiDef]

HiDef,
"A simple formula cannot be used to convert between P.E.P. and average values on complex waveforms such as voice ssb." --
I know. So using voice as the audio signal source is kind'a silly, isn't it! So don't use a complex wave form (voice), use a 'simple' wave form for testing instead.
And just for grins. Those formulas are accurate for any instantaneous time period reading in any kind of wave form. Seems like if you wanted the 'average' power figure you'd use an 'averaging'/RMS meter (Bird 43??), wouldn't you say? Oops! Better not do that, then you'd end up with them 'Bird watts', right?
(Measure a carrier signal on both an RMS and Pep meter. If they aren't the same reading, better check that Pep meter, it ain't right.)
- 'Doc

So how do you measure your 1500 watts P.E.P. in order to comply with FCC rules when using ssb?

What is an instantaneous time period?

Consider the RMS value of a square wave verses a sine wave an an example of why simple math won't work with or without time involved.

 

[W5LZ]

I use CW for measuring output power. Not everyone can, but it's the simplest way of doing it. Or, use a 'tone' as the audio for SSB input. 'Nuther one of those not everyone can do it, but it certainly works, using an RMS meter too.
(Not the 'best' by any means but a phone's dial tone is one source for that 'audio tone' and SSB/AM power output measuring. Deals with that dial tone being 'corrupted' by extraneous noises and that it's a 'two-tone' thingy.)
I can't think of a single time I've ever transmitted a 'square wave' intentionally. Not to say that I haven't, but at least not intentionally. Even with a square wave, after the initial 'garbage' at the very beginning of it, and at the end, the constant portion between those two points would work just dandy for measuring purposes.
'Instantaneous time', is a bad way of saying a single point (of very short duration) in the transmitted signal. Just one 'point' along that 'wave'. Those formulas work just fine there. If you select that 'point' at the peak of the transmitted 'wave', you got 'half' of the Pep power. Take those readings over a longer period of time, average them and you got 'average' power. You have to 'manipulate' the "+" and "-" values, but that's fairly easy to understand how to do (only measure the "+" values and multiply by two). Which is what those 'Pep' or peak-reading meters are supposed to be doing, right?
- 'Doc

 

[BOOTY MONSTER]

http://www.firecommunications.com/rmspwr.pdf

 

[HiDef]

I use CW for measuring output power. Not everyone can, but it's the simplest way of doing it. Or, use a 'tone' as the audio for SSB input. 'Nuther one of those not everyone can do it, but it certainly works, using an RMS meter too.
(Not the 'best' by any means but a phone's dial tone is one source for that 'audio tone' and SSB/AM power output measuring. Deals with that dial tone being 'corrupted' by extraneous noises and that it's a 'two-tone' thingy.)
I can't think of a single time I've ever transmitted a 'square wave' intentionally. Not to say that I haven't, but at least not intentionally. Even with a square wave, after the initial 'garbage' at the very beginning of it, and at the end, the constant portion between those two points would work just dandy for measuring purposes.
'Instantaneous time', is a bad way of saying a single point (of very short duration) in the transmitted signal. Just one 'point' along that 'wave'. Those formulas work just fine there. If you select that 'point' at the peak of the transmitted 'wave', you got 'half' of the Pep power. Take those readings over a longer period of time, average them and you got 'average' power. You have to 'manipulate' the "+" and "-" values, but that's fairly easy to understand how to do (only measure the "+" values and multiply by two). Which is what those 'Pep' or peak-reading meters are supposed to be doing, right?
- 'Doc

OK. I see what you are trying to get across on single point. You seem to want to get some snapshot of time mixed in there. Probably because that helps seeing power delivery like RMS really is. This whole idea quickly runs into calculus and integration. Basic mathematics cannot be applied.

You could easily be violating the rules if you are near the 1500 watt limit. Your sinewave test tone isn't telling you what the peak power will be when switching to voice. Voice isn't anywhere close to a sinewave. Never was. Voice contains fundamentals and harmonics even within that narrow passband used for communications. It also has a different waveform on each side of zero. Yes, a tone into an ssb tx produces CW and a few spurs which can be ignored for this measurement.

An oscilloscope setup to measure R.F voltage can easily prove this. Sample some ssb R.F. with a test tone and watch what happens when you go to voice. You can set the system for 1500 watts on a Bird 43, R.F. ammeter or weapon of your choice. Go over to voice and the peaks can easily break the speed limit. Now, try it with a peak hold circuit like VK1OD recommends. The better ones track the scope within several percent. Bird even makes one. Its called the 4314. My station uses a peak reading 43 clone Coaxial Dynamics right beside a regular 43 without a peak reading circuit. It's really telling when looking at both at the same time. One foot away on the console is a Tektronix 465 looking at R.F. amplitude at 50 ohms through a Bird 4275 sampler.

The only time it would be safe to count on a tone measurement setting absolute peak power in an ssb system would be where the amplifier itself runs into gain compression because it's out of poop. Unfortunately those are all over the ham bands. That along with the ALC fixes everything from overdrive to warts mentality can make for some wonderful occupied bandwidth. Might as well just use a Davemade.

I'm only mentioning square waves as an illustration of what happens to RMS power. I'm not saying you are transmitting them

I'm considering just putting all this up on a page somewhere. Maybe a video of a good amateur R.F. measurement setup and it's limitations...........