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Author Topic: 1500 pep output max  (Read 94920 times)
K6UJ
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Posts: 1377




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« Reply #45 on: December 31, 2015, 04:49:16 PM »

I think we are at the gist of it now.  Had I been aware of the ITU language, I would have asked the question to say has anyone petitioned the fcc to make the power level based on mean power.  The question is to address that the average power is 20-30% under pep.  I apologize if I started us down the rabbit hole not being sure whether I should refer to it as average or rms power.  My bad.  


Going back to my question, I wonder if one could measure mean  power properly for ssb?  And, .25s doesn't "feel" like a long enough interval.

Mean or average power in reference to SSB doesn't work as a good way to measure output power because it is dependent upon the characteristics of an individuals voice. Not easy to measure.  Peak power is not easy to measure with much accuracy either.  The FCC probably should have just left the old way of measuring power in place because it was simpler and only common cheap metering needed to be used to measure average input for SSB.  
[/quote

The FCC doesn't base their decisions on what's simpler or cheaper.
:-) :-).   
Bob
K6UJ
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KK4YDR
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Posts: 673




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« Reply #46 on: December 31, 2015, 04:51:20 PM »

The  only instance I can come up with for ERP as the rule is the 5 channels on 60 meters.
That is done for a totally different purpose to limit QRM to other services in the same band as well as the frequency and bandwidth has to be precision to specified  limits.
Good luck.

Yeah i'm quite sure if they didn't limit ERP and wen't with pep there would be split splatter all over the place. The band would look like someone is frying water in oil. Hell 80 meters looks like this all the time.
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W9IQ
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« Reply #47 on: December 31, 2015, 05:36:27 PM »

PEP is easy to measure. See my earlier post in this thread.

Average power for SSB could be measured but it would take a fast enough processor and a more rigorous definition for average power.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
AA6CJ
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Posts: 95




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« Reply #48 on: January 01, 2016, 06:06:07 AM »

Yeah, that get us back to what time interval to average across.  How do you get consensus on that?  Assuming Ssb is ultimately replaced by a digital voice waveform, that waveform pep might be like rtty and cw.
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W9IQ
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« Reply #49 on: January 01, 2016, 06:16:06 AM »

Since our Amateur Radio community is sadly lacking in standards, I don't expect concensus on average power to be imminent. Consider that S meter "standard" is only a techical recommendation and look how poorly that is followed.

Also consider that their are dozens of modulation modes that would need to be addressed.

That is why I like PEP - clearly defined and simple to measure regardless of the modulation mode.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
SM0AOM
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Posts: 261




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« Reply #50 on: January 01, 2016, 06:28:04 AM »

Yeah, that get us back to what time interval to average across.  How do you get consensus on that?  Assuming Ssb is ultimately replaced by a digital voice waveform, that waveform pep might be like rtty and cw.

It is highly unlikely that a vocoder and a channel coder good enough to get a telephone quality DV data stream into a constant-envelope RF waveform suitable for transmission on HF will surface in the forseeable future.

Current DV technology for HF channels needs a 2400-3600 bps channel capacity, and this takes a multitone or PSK/QAM modem to achieve this throughput. These modems use a waveform that has a peak-to-average ratio which is about the same as SSB voice, and since distorsion is a critical parameter PEP will still be the most suitable power measure.

It may very well be that the end of amateur radio comes before the end of analog SSB.
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AA6CJ
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« Reply #51 on: January 01, 2016, 04:05:33 PM »

Thanks, the average power might be the same, but aren't all the QAM tones sent out at full pep? 

If you averaged the power out of cw you'd be counting the time between the dits and dahs. 

OM I'm listening...got my attention with the digital waveform....   Cheesy

We may all die off before ssb's demise but hopefully not HR.  I read recently how big a deal it was to switch from am to Ssb.
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SM0AOM
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« Reply #52 on: January 02, 2016, 12:58:39 AM »

QAM is one method to approach the Shannon limit in a modulated waveform, and the more noise-like the waveform is, the closer to this limit you are getting. White noise has a long term peak-to-average ratio of about 13 dB, so to use a power amplifier efficiently it is necessary to use some processing in the time domain, frequency domain or both. The goal is to reduce the peak-to-average ratio without introducing undue distorsion.

Each carrier in a multitone or OFDM modem can be modulated in different ways, ranging from FSK to multilevel QAM,but all have in common that they may add in phase which may create a very high peak-to-average ratio. This is avoided by various forms of processing. The PEP in unprocessed waveforms can be very high compared to the average power, and this is unfavourable in peak power and distorsion limited transmitter, which most practical systems contain.

CW or Morse can use any averaging time desired, but with long averaging times, such as minutes, hours or days, we end up in impractical relations between peak and average power. Intra-character spaces and listenng pauses would then enter the pricture.

A practical approach that I believe is used almost universally is to average the power reading for Morse transmissions over a time interval equal to the length of the shortest signalling element used. This would take into account dynamic electrical and thermal stresses of the output devices. For evaulating thermal stresses in the power supply or the cooling system, longer averaging times, up to several minutes, may be appropriate.
« Last Edit: January 03, 2016, 09:11:06 PM by SM0AOM » Logged
AA6CJ
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Posts: 95




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« Reply #53 on: January 02, 2016, 04:47:45 PM »

If all of the points of the constellation of QAM are sent at the same amplitude, then wouldn't that amplitude be 1500 pep? 

I've read that the average power of Ssb is actually 20-30 percent of Pep because of variations in voice sound level at various frequencies as we speak.  You are way way beyond me in understanding, I'm just trying to understand how we could get more power for  ssb contesting.  I guess I envy the power of cw and rtty that is allowed because they are binary. 0 or 1500 watts.  Voice is far from that.  I originally thought that we could address this by looking at it from an average power perspective.  Not a good idea based on the technical challenges of measuring it as discussed in the thread.

Digital voice is really as a side thought, but one I'm interested in.
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KM1H
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« Reply #54 on: January 02, 2016, 07:57:50 PM »

Quote
I've read that the average power of Ssb is actually 20-30 percent of Pep because of variations in voice sound level at various frequencies as we speak.


That is without any processing which can raise it to 50% and still sound good.

Quote
I'm just trying to understand how we could get more power for  ssb contesting.

Crank up the processor until your taking out 5-10 kHz and eliminating interlopers. That is the prime directive of contesting these days as it not only raises your average power to almost PEP but you win the game of bumper cars or mines bigger Roll Eyes

Carl

 
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W6RZ
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Posts: 365




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« Reply #55 on: January 02, 2016, 09:42:31 PM »

If all of the points of the constellation of QAM are sent at the same amplitude, then wouldn't that amplitude be 1500 pep?

You're probably thinking of QPSK, where the four constellation points are at the same power level. But you can't send the raw symbols, it would take way too much bandwidth. You have to filter the symbols to limit the bandwidth, and the typical filter for QPSK (and QAM) is the root raised cosine filter.

The roll-off factor of the RRC filter determines the PAPR level. For the 0.35 roll-off that's used on DVB-S, the PAPR is around 4.5 dB. Sharper roll-offs increase the PAPR.

Here's a 100 tap RRC at 0.35 roll-off. Symbol rate is 12 Msyms/s and the bandwidth is 16.2 MHz.

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AA6CJ
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« Reply #56 on: January 03, 2016, 07:58:30 AM »


Quote
You're probably thinking of QPSK, where the four constellation points are at the same power level. But you can't send the raw symbols, it would take way too much bandwidth.

That's exactly what I was assuming.  Thanks for taking the time to explain it.  The light bulb came on....
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AA6CJ
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« Reply #57 on: January 03, 2016, 08:07:29 AM »

Quote
I've read that the average power of Ssb is actually 20-30 percent of Pep because of variations in voice sound level at various frequencies as we speak.


That is without any processing which can raise it to 50% and still sound good.

Quote
I'm just trying to understand how we could get more power for  ssb contesting.

Crank up the processor until your taking out 5-10 kHz and eliminating interlopers. That is the prime directive of contesting these days as it not only raises your average power to almost PEP but you win the game of bumper cars or mines bigger Roll Eyes

Carl

 


Carl I think you've nailed it here.  K9EID, has started doing a series on audio articulation.  Limiting the audio to those frequencies that convey through articulation and then applying some compression or limiting the pep peaks judiciously on top of that might be the secret sauce.  But already what you describe is 3db, and according to a contest university presentation I watched recently, each dB increases score by 6%!

thanks OM,
Fred
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WB4JTR
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Posts: 37




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« Reply #58 on: January 03, 2016, 03:11:43 PM »

Putting RMS vs. peak power into perspective....

A continuous tone on SSB with a PEP of 1500 watts will provide an RMS output of 750 watts, which is "3 db"  "less", so it would take 3 KW PEP to achieve 1500 watts RMS with a single tone...


Brian K6BRN

Not true.  Remember, PEP is defined as the RMS [ed- " RMS-based"] power at the peak of the envelope.  So a single tone from a 1500W SSB transmitter is 1500W (by RMS).
« Last Edit: January 18, 2016, 08:03:30 PM by WB4JTR » Logged
KM1H
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Posts: 5549




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« Reply #59 on: January 05, 2016, 05:22:38 PM »

Here we go again with an audiophool version of reality....Im not saying your one but that version grew fast wings from them
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