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Author Topic: 1500 pep output max  (Read 94917 times)
KB8E
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Posts: 50




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« Reply #75 on: January 15, 2016, 02:40:25 AM »

WB4JTR is correct. PEP is power overaged over one RF cycle at the peak of the modulation envelope. In other words, very short-term average power at the peak of the modulation. (Note: not instantaneous peak power as I stated in my first post in this topic. Sorry for that error and thanks to those who corrected me.) Think of the case of an unmodulated carrier; Since the modulation envelope is constant, any measurement of average power is correct. If the carrier is modulated, PEP represents the average power at the peak, as if the peak were to be sustained.

Sam
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W5HRO
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Posts: 47




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« Reply #76 on: January 15, 2016, 05:54:04 AM »

because the waveform is ALWAYS just a sinewave.  (A sinewave contains no harmonics.)

No it is not and that's where you are wrong. You are right that a sinewave does not contain any 3rd order harmonics (be specific), but the PEP waveform is NOT always a sinewave.

I think most of us probably understand that you are referring to SSB and not AM and I'm only speaking for myself, but average power is mean power and is not PEP. Forget the fact that some people including myself tend to generalize avg/mean power as RMS power in discussions, but you have misinterpreted some basic facts.

A sinewave doesn't contain ANY harmonics.  Even harmonic distortion is also limited by the FCC.  If both odd and even orders weren't so limited, the single cycle on which PEP is based would be distorted, making the PEP calculation more difficult.

You keep repeating that average or mean power is not PEP.  That is true (as I have also repeated).  But PEP IS average (mean) power under the specific condition imposed by the ITU (and FCC).  By definition.  It is also RMS-derived power under the same condition.

I think the main problem here is failure to realize the time scale difference between the two concepts.  The average (mean) power used to define PEP is one RF cycle.  This is also the time scale used to establish the well-known peak/average/RMS sinewave relations.  The general audiophile concept of average power is based on a time scale of thousands of RF cycles.  And sometimes the RF waveform is ignored completely and averages are based on envelope or modulating audio alone.

In a way we're lucky PEP is based on the average (RMS) power at the envelope peak.  Think what our 1500 watts would get us if it were based on the instantaneous peak power of that single cycle!

A sinewave CAN contain even harmonics, but in RF applications it is not very critical. It is the sharp and/or flat edges of the instantaneous peaks in PEP that are the issue and like when someone overdrives their linear to where it flat-tops. Those will produce the 3rd order harmonics. Even order harmonics can be a good thing, but mainly in audio applications.

Forget what the FCC and the ITU say because it is insignificant. That's been the problem from the very beginning. In the REAL world PEP is NEVER a perfect one-cycle sinewave like you keep suggesting. RMS and PEP all do come from the same set of equations, but in the REAL world PEP with the human voice consists of instantaneous peaks which has nothing to do with average power unless you measure that average power, but it's still not PEP or what most people consider PEP to be.

You need to separate the in the clouds theoretical and the screwed-up FCC and ITU descriptions from the REAL world practical way things really are.
« Last Edit: January 15, 2016, 06:56:39 AM by W5HRO » Logged

WB4JTR
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Posts: 37




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« Reply #77 on: January 15, 2016, 10:15:50 AM »

WB4JTR is correct. PEP is power overaged over one RF cycle at the peak of the modulation envelope. In other words, very short-term average power at the peak of the modulation. (Note: not instantaneous peak power as I stated in my first post in this topic. Sorry for that error and thanks to those who corrected me.) Think of the case of an unmodulated carrier; Since the modulation envelope is constant, any measurement of average power is correct. If the carrier is modulated, PEP represents the average power at the peak, as if the peak were to be sustained.

Sam

Thank you Sam.  That is all I am trying to say.  All my statements are in the context of the post #14 which I endever to refute.  The original poster can speak for himself, but I can speculate where he went wrong:
If you ignore the RF waveform and base your calculations on the modulating single-tone sinewave, you could conclude that power derived from the RMS calculation is half the peak power.  But that is just flat wrong for a SSB signal.  The ITU (and FCC) got it right for calculating the difference between PEP and average (RMS-derived) power in this case.  The difference is exactly zero -- not 3dB.

Let's not go down the rabbit hole of long-term average power of voice-modulated envelopes of the sinewave RF waveform.  It's different for each voice and exact calculations require mathematics of which most hams (and more audiophiles) are unaware.

But the ITU got it right and expressed it correctly.  Deleting the word "average" from the text, as was suggested earlier, would break the analysis.

-Lee
« Last Edit: January 15, 2016, 11:36:12 AM by WB4JTR » Logged
WB4JTR
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Posts: 37




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« Reply #78 on: January 15, 2016, 10:27:02 AM »


A sinewave CAN contain even harmonics, but in RF applications it is not very critical. It is the sharp and/or flat edges of the instantaneous peaks in PEP that are the issue and like when someone overdrives their linear to where it flat-tops. Those will produce the 3rd order harmonics. Even order harmonics can be a good thing, but mainly in audio applications.

Forget what the FCC and the ITU say because it is insignificant. That's been the problem from the very beginning. In the REAL world PEP is NEVER a perfect one-cycle sinewave like you keep suggesting. RMS and PEP all do come from the same set of equations, but in the REAL world PEP with the human voice consists of instantaneous peaks which has nothing to do with average power unless you measure that average power, but it's still not PEP or what most people consider PEP to be.

You need to separate the in the clouds theoretical and the screwed-up FCC and ITU descriptions from the REAL world practical way things rea inlly are.

See message 77 above.

PS:  A single sinewave never contains even or odd harmonics.  It takes a summation of sinewaves to represent any harmonic distortion.  And even harmonics of the RF signal are harder to filter than odds -- the first one is closer to the fundamental.  I think you have confused harmonics with IMD.
« Last Edit: January 15, 2016, 10:42:36 AM by WB4JTR » Logged
W5HRO
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Posts: 47




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« Reply #79 on: January 15, 2016, 11:04:24 AM »

A perfect symmetrical waveform will not produce any harmonics even or odd, but a perfect symmetrical waveform does NOT exist in the real world and that's what you keep missing Roll Eyes

In the REAL world with 80% to 90% hams running tube linears biased in AB2 the lower operating point of AB2 introduces harmonic distortion to the modulated waveform anyway. However, if the distortion is not distortion from flat-topping or from other anomalies that create sharp edges then the distortion will generally be of even-order which can be a good thing. What it will do is increase the modulated bandwidth and audio fidelity. However, for every repetition of the fundamental frequency there are two repetitions of the 2nd harmonic along with three repetitions of the 3rd harmonic, but the level of those 3rd harmonic repetitions are usually so low they are insignificant.

Now, if someone over-drives their tube AB2 linear into flat-topping and/or produces sharp edges like many hams operating on SSB do today then It will produce lots of trash that will show up on a spectrum analyzer. That or if they are using and over-driving solid-state audio equipment and/or solid-state linears. It will always be 3rd order and much worse. One of the benefits of using vacuum tube equipment is that you can generate the even-order harmonics and obtain better fidelity doing so. That is one area where some Audiophiles actually no more than some Radiophools.
« Last Edit: January 15, 2016, 11:24:33 AM by W5HRO » Logged

WB4JTR
Member

Posts: 37




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« Reply #80 on: January 15, 2016, 11:32:08 AM »

A perfect symmetrical waveform will not produce any harmonics even or odd, but a perfect symmetrical waveform does NOT exist in the real world and that's what you keep missing Roll Eyes

In the REAL world with 80% to 90% hams running tube linears biased in AB2 the lower operating point of AB2 introduces harmonic distortion to the modulated waveform anyway. However, if the distortion is not distortion from flat-topping or from other anomalies that create sharp edges then the distortion will generally be of even-order which can be a good thing. What it will do is increase the modulated bandwidth and audio fidelity. However, for every repetition of the fundamental frequency there are two repetitions of the 2nd harmonic along with three repetitions of the 3rd harmonic, but the level of those 3rd harmonic repetitions are usually so low they are insignificant.

Now, if someone over-drives their tube AB2 linear into flat-topping and/or produces sharp edges like many hams operating on SSB do today then It will produce lots of trash that will show up on a spectrum analyzer. That or if they are using and over-driving solid-state audio equipment and/or solid-state linears. It will always be 3rd order and much worse. One of the benefits of using vacuum tube equipment is that you can generate the even-order harmonics and obtain better fidelity doing so. That is one area where some Audiophiles actually no more than some Radiophools.


As I suspected, you have presented a general discussion of IMD.  It's mostly true, but out of context in the present discussion.

Please see message #77 above.
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W5HRO
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Posts: 47




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« Reply #81 on: January 15, 2016, 01:08:21 PM »

As I suspected, you have presented a general discussion of IMD.  It's mostly true, but out of context in the present discussion.

It has nothing to do with that and I was right on point. You have been referring to a perfect symmetrical sinewave from the FCC and ITU specs which does NOT exist with either the human voice (voice communications) or music.

If a perfect symmetrical sinewave did exist the amplifier bias class (or operating point) of what ham operators actually use would distort it one way or another anyway. Only class A amplifiers can come close to producing an exact replica of a perfect symmetrical sinewave if a perfect symmetrical sinewave was inputted.

The main point is that the human voice does not produce a symmetrical sinewave so quoting what is written in the FCC and ITU specs does not apply because they are not real world representations of what actually happens.
« Last Edit: January 15, 2016, 01:10:44 PM by W5HRO » Logged

WB4JTR
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Posts: 37




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« Reply #82 on: January 15, 2016, 03:15:32 PM »

As I suspected, you have presented a general discussion of IMD.  It's mostly true, but out of context in the present discussion.

It has nothing to do with that and I was right on point. You have been referring to a perfect symmetrical sinewave from the FCC and ITU specs which does NOT exist with either the human voice (voice communications) or music.

If a perfect symmetrical sinewave did exist the amplifier bias class (or operating point) of what ham operators actually use would distort it one way or another anyway. Only class A amplifiers can come close to producing an exact replica of a perfect symmetrical sinewave if a perfect symmetrical sinewave was inputted.

The main point is that the human voice does not produce a symmetrical sinewave so quoting what is written in the FCC and ITU specs does not apply because they are not real world representations of what actually happens.

There is absolutely no requirement for a perfect RF sinewave.  It only has to be close enough to satisfy the FCC regs.  That is plenty close enough to allow use of the sinewave relations for peak/RMS/average.  The calculations will be far more accurate than any 'scope, spectrum analyzer, or meter (even after corrections for average-responding movements).

And even if you suspect your waveform doesn't meet FCC regs, here's the surprise:
The ITU regulators were pretty smart.  Even if the RF cycle of interest is not a good sinewave, the calculation for PEP still works!  This is a result of the definition being based on average power of a single cycle (the basic concept of RMS).

So the ITU definition is robust.  If you suspect your RF cycle is not clean enough, just break out the calculus and follow the definition explicitly.  Your result will still be true PEP -- just realize all of the power won't be on the operating frequency.  Some of the PEP will be out of the band at the harmonics of your frequency (in violation of the regs).

Don't confuse the single cycle used for the PEP definition with the audio modulation waveform and IMD effects.  Also realize PEP is defined at the output to the antenna -- after harmonic filtering.
« Last Edit: January 15, 2016, 03:49:35 PM by WB4JTR » Logged
W5HRO
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Posts: 47




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« Reply #83 on: January 15, 2016, 06:56:11 PM »

There is absolutely no requirement for a perfect RF sinewave.  It only has to be close enough to satisfy the FCC regs.  That is plenty close enough to allow use of the sinewave relations for peak/RMS/average.  The calculations will be far more accurate than any 'scope, spectrum analyzer, or meter (even after corrections for average-responding movements).

I never said there was, you did.

Quote
And even if you suspect your waveform doesn't meet FCC regs, here's the surprise:
The ITU regulators were pretty smart.  Even if the RF cycle of interest is not a good sinewave, the calculation for PEP still works!  This is a result of the definition being based on average power of a single cycle (the basic concept of RMS).

It's pointless trying to meet that so called FCC requirement because it is not valid in the real world.

Quote
So the ITU definition is robust.  If you suspect your RF cycle is not clean enough, just break out the calculus and follow the definition explicitly.  Your result will still be true PEP -- just realize all of the power won't be on the operating frequency.  Some of the PEP will be out of the band at the harmonics of your frequency (in violation of the regs).

Only a meter that can measure true Average power will be accurate. Another member already posted one previously. PEP is a nonsense measurment and it's pointless trying to meet it.

Quote
Don't confuse the single cycle used for the PEP definition with the audio modulation waveform and IMD effects.  Also realize PEP is defined at the output to the antenna -- after harmonic filtering.

I'm not confusing anything. The only person who has been confused is you.
« Last Edit: January 15, 2016, 07:02:47 PM by W5HRO » Logged

W9IQ
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Posts: 3553




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« Reply #84 on: January 15, 2016, 08:24:09 PM »

You may wish to debate your preferred method of power measurement but in the end, PEP limits are a regulatory requirement in the US. Until you convince the FCC to change the regulations, your "better" way doesn't convey any regulatory significance - at best it could be described as an additional metric.

The good thing is that PEP is well defined, it is relatively easy to measure, it works for all modulation modes, and it spans all amplifier classes. It is also independent of voice characteristics, assuming all voices are capable of the same modulation peak (ideally 100% modulation) at some time in their speech pattern (particularly applicable to SSB).

You can of course use various processing techniques to improve your average output power and still meet the PEP limits set forth in the regulations. Coincidentally, there is a nice article by W9GR on CESS for SSB in the February 2016 issue of QST to this very point. Dave sites a ~3.6 dB improvement in average power for the same PEP power while eliminating the need for ALC. The takeaway for this thread is that the technique can still meet the PEP regulatory requirement while improving average power (and most likely the receiver's S meter reading).

- Glenn W9IQ



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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
WB4JTR
Member

Posts: 37




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« Reply #85 on: January 15, 2016, 08:39:38 PM »

There is absolutely no requirement for a perfect RF sinewave.  It only has to be close enough to satisfy the FCC regs.  That is plenty close enough to allow use of the sinewave relations for peak/RMS/average.  The calculations will be far more accurate than any 'scope, spectrum analyzer, or meter (even after corrections for average-responding movements).

I never said there was, you did.

Quote
And even if you suspect your waveform doesn't meet FCC regs, here's the surprise:
The ITU regulators were pretty smart.  Even if the RF cycle of interest is not a good sinewave, the calculation for PEP still works!  This is a result of the definition being based on average power of a single cycle (the basic concept of RMS).

It's pointless trying to meet that so called FCC requirement because it is not valid in the real world.

Quote
So the ITU definition is robust.  If you suspect your RF cycle is not clean enough, just break out the calculus and follow the definition explicitly.  Your result will still be true PEP -- just realize all of the power won't be on the operating frequency.  Some of the PEP will be out of the band at the harmonics of your frequency (in violation of the regs).

Only a meter that can measure true Average power will be accurate. Another member already posted one previously. PEP is a nonsense measurment and it's pointless trying to meet it.

Quote
Don't confuse the single cycle used for the PEP definition with the
 audio modulation waveform and IMD effects.  Also realize PEP is defined at the output to the antenna -- after harmonic filtering.

I'm not confusing anything. The only person who has been confused is you.

If I ever said a perfect RF sinewave is required I was wrong.  That requirement would mean the FCC regs call for infinite attenuation in the harmonic filtering.  Truly impractical.  The harmonic content is only LIMITED by regulation.  And that limit is low enough that the sinewave RMS/average/peak relations can be used in practice.  But as I demonstrated above, if you are so concerned about the purity of the sinewave, don't worry -- the ITU definition still describes a perfectly accurate PEP.  You don't really have to use the sinewave relations to get there -- it's just a little more difficult calculation.

Meeting the ITU/FCC maximum PEP requirement is not pointless.  It is done regularly and successfully all over the world.  Just be aware of the accuracy limit of your measurement system and stay that far below the limit -- you'll be safe.

PEP measurement is not nonsense.  CW power output can be measured accurately enough and used as a reference on any old 'scope to set a reference for accurate PEP 2-tone, multi-tone, or voice/music measurements.  Even band-limited white noise can be used to check PEP, if desired.

I assumed your presentation on audio and envelope distortion caused by non-linearity and IMD effects to be due to confusion of the modulation waveform with the RF waveform cycle on which PEP is defined.  My bad...I guess it was just a non sequitur.
« Last Edit: January 15, 2016, 08:46:23 PM by WB4JTR » Logged
W5HRO
Member

Posts: 47




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« Reply #86 on: January 16, 2016, 07:59:32 AM »

You can just keep going on and on here and you have already contradicted yourself once or twice but you are still wrong nevertheless.

PEP is in fact a real measurement if you inject a perfect symmetrical waveform using a generator, but it's shape will still be slightly altered (distorted) after going through the audio and RF amplifier circuits ham operators use so in the end it will not be an exact replica of what was inputted, but it will be close enough for a so-so-measurement. It will never be 100% textbook exact though.

What blows PEP out of the water and its use as a measurement in the real world is the fact that the human voice produces an asymmetrical waveform that’s shape and level constantly changes as a person talks so the only real way to measure it is to take an average measurement of it over a time period and not just using one single cycle. A good and true avg/mean power reading meter will work the best.

You yourself can kept debating otherwise, but in the end you will still be wrong no matter what you say.

Have a good one...

73's
« Last Edit: January 16, 2016, 08:01:39 AM by W5HRO » Logged

WB4JTR
Member

Posts: 37




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« Reply #87 on: January 16, 2016, 09:31:52 AM »

You can just keep going on and on here and you have already contradicted yourself once or twice but you are still wrong nevertheless.

PEP is in fact a real measurement if you inject a perfect symmetrical waveform using a generator, but it's shape will still be slightly altered (distorted) after going through the audio and RF amplifier circuits ham operators use so in the end it will not be an exact replica of what was inputted, but it will be close enough for a so-so-measurement. It will never be 100% textbook exact though.

What blows PEP out of the water and its use as a measurement in the real world is the fact that the human voice produces an asymmetrical waveform that’s shape and level constantly changes as a person talks so the only real way to measure it is to take an average measurement of it over a time period and not just using one single cycle. A good and true avg/mean power reading meter will work the best.

You yourself can kept debating otherwise, but in the end you will still be wrong no matter what you say.

Have a good one...

73's

PEP has no "shape".  It is a number: "watts"' easily measured and independent of audio or envelope shape or distortion.

You should take your discussions of audio harmonic and IMD distortion to another thread. They are non sequiturs here.  There is certainly some truth in them but they can only relate to "strawmen" here.

Your proposed procedure of "The only real way to measure it is to take an average measurement of it over a time period and not just using one single cycle." Will not produce anything close to PEP.

The purpose of this thread is to explain why single-tone SSB is not 3dB below PEP.  I think that has been accomplished.

Move on.

« Last Edit: January 16, 2016, 09:57:58 AM by WB4JTR » Logged
KM1H
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Posts: 5546




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« Reply #88 on: January 16, 2016, 11:49:45 AM »

PEP is power overaged over one RF cycle at the peak of the modulation envelope. In other words, very short-term average power at the peak of the modulation.

Sam

Of course that definition is correct as it is clearly spelled out in the FCC rules for decades now to anyone who takes the time to look it up.

However this cant be defined as RMS power since it simply has not been defined in engineering textbooks, journals, FCC, nor the IEEE.
IOW it is purely an invented term with no basis in fact and simply a carry over from Sears and other audio amp manufacturers who jacked up the power using a marketing managers formula squeezed out on the throne one morning. They carried it over to horsepower also.

Im still waiting for a legitimate citation from a USA source (not an individual) that claims otherwise. I say USA since this is about a FCC rule. If Im wrong an apology will be forthcoming. Meanwhile please stop all the meaningless verbal dancing, damage control or whatever else someone wishes to call it.

Carl
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K4KYV
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Posts: 116




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« Reply #89 on: January 16, 2016, 04:29:58 PM »

...it is purely an invented term with no basis in fact and simply a carry over from Sears and other audio amp manufacturers who jacked up the power using a marketing managers formula squeezed out on the throne one morning...

Like the p.e.p. amateur radio power rule.

Quote
I say USA since this is about a FCC rule.

As far as I know the USA was the first country to adopt p.e.p. as the amateur radio power standard, then other countries followed suit and adopted into their rules. Totally irrelevant to the fundamental purpose of a power limit in the rules of the amateur or any other radio service.
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