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Author Topic: 1500 pep output max  (Read 94425 times)
AA6CJ
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Posts: 95




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« Reply #315 on: February 26, 2016, 07:33:54 PM »

In general when we are discussing RF power and SSB, "average power" is usually meant to be the average over some significant time period, usually something like the length of a full sentence of speech.  We use the term Peak Envelope Power as the highest instantaneous (one RF cycle) power generated by a transmitter during that sentence.  (Let's not get wrapped up in the duration of the average - I'm presenting the general concept here.)

To be meaningful, the term "average" power must be integrated over a defined time period that is relevant to the quantity being measured.  For example,  with CW, we could mean the average power over an entire transmission, which would include spaces between characters, words and sentences.  We could even define it as the average power over a QSO, including periods of reception.  Obviously, those definitions would have little meaning in terms of effective transmitter output power.  The chosen time period must be relevant to the nature of the transmitted data.  With CW, the relevant time period would be the duration of the shortest character of the normally transmitted  signal, i.e. a single dit.  With SSB voice, the relevant factor would be a function of the syllabic rate of human speech.

With SSB voice under the 1 KW DC input rule, the FCC addressed the issue of "input power" in a letter to ARRL:

  The following ... may be considered as a presently acceptable method for determining the d.c. plate power input to the final r.f. stage of a single-sideband  amateur transmitter:
  The maximum d.c. plate power input to the (RF) tube(s) supplying power to the antenna system of a (SSB) suppressed-carrier transmitter, as indicated by the usual plate voltmeter and plate milliammeter, shall be considered as the "input power" insofar as ... the Commission's rules are concerned, provided the plate meters utilized have a time constant not in excess of approximately 0.25 second, and the linearity of the transmitter has been adjusted to prevent the generation of excessive sidebands.  The "input power" shall not exceed one kilowatt on peaks as indicated by the plate meter readings.


- Single Sideband for the Radio Amateur (ARRL), second edition 1958, page 14

Average output power from a transmitter is generally proportional to the DC input to the final stage, assuming a consistent efficiency factor. That was the basis for the amateur power limit for many decades and served the purpose well. The 0.25 second (250 ms) time constant prescribed in the FCC statement is consistent with the concept of the audio V-U meter used  in audio recording and broadcasting, in which by definition the mass of the meter movement effectively integrates the signal with a rise time of 300 ms.

Here is a treatise which may be of interest, from the BBC in 1963, on the subject of VU meters, peak-reading meters and loudness measurements:
http://www.mwigan.com/mrw/Publications__49_Edmund_Ramsay_Wigan_files/1963-29.pdf


How cool that you digged up this FCC statement.  The .250 ms time constant could still be used today and applied to PEP output.  The BBC paper makes a good case for PPM vs VU, But ignoring that for now....  I wonder how much increase in average power would result?  If someone had simulink it might be pretty straight forward to analyze.
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AA6CJ
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« Reply #316 on: February 26, 2016, 07:44:20 PM »

PEP seems to me to be a perfectly reasonable way of slapping a limit on transmitters which can operate in many, many different modes...

Silly thought but how about a limit in terms of power per Hz of occupied bandwidth...
73 Dan.
Agreed and not silly.  However, 1500 watts concentrated in a 30hz CW...is akin to a laser beam.  I could see one getting addicted to power like that.  Hi!
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AA6CJ
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« Reply #317 on: February 26, 2016, 07:51:16 PM »

"I see this as a discussion of power parity between modes...Now, you will have to define what you think parity between modes might be.  Do you mean that all modes should be given a power level that allows them the same communications capability at some distant point on the earth?  What is the base reference?  JT65, PSK31, SSB voice, Full Carrier AM, NBFM, Spread Spectrum?  I'm not trying to be silly here but what are you concerned about SSB achieving parity with?

Obviously each mode has different communications capability under different propagation and noise conditions.  I saw reference earlier to comparing the average power of RTTY with the average power of SSB.  RTTY is a 100% average power mode.  Under most conditions a 1500 watt PEP SSB signal gets through better than a 1500 watt RTTY signal.  That difference is why RTTY stations typically run high power.  It is necessary even with modern computer based decoding programs.  On the other hand, a 150 watt PSK31 signal would likely get through more reliably than a 1500 watt SSB signal.  Most PSK31 operation is with power levels below 50 watts and world wide DXing is possible.  Each mode has its advantages and disadvantages for different purposes and under different conditions.

So, the question is: Parity with what?

Gary - N0GW

I expected this question.  All valid points.  As I understand it in the PSK31 it would be considered terrible manners and completely unnecessary to run high power.
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K4KYV
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« Reply #318 on: February 27, 2016, 09:54:55 PM »

How cool that you digged up this FCC statement.  The .250 ms time constant could still be used today and applied to PEP output.  The BBC paper makes a good case for PPM vs VU, But ignoring that for now....  I wonder how much increase in average power would result?  If someone had simulink it might be pretty straight forward to analyze.

Or more meaningfully, to average power.  It would be based on a true-RMS reading RF voltmeter or ammeter, with no more than a 0.250 time constant. The thermocouple RF ammeter is too sluggish, so it would likely be accomplished with some type of active DSP circuit.  Problem with the "average power" function with conventional meters like the Bird 43, is that it actually reads simple average voltage rectified with a diode, not true RMS. What confuses most people is that average power is derived from RMS voltage/current, NOT average (absolute value of) voltage/current. And, as we discussed before, there is no such thing as RMS power or RMS watts, and average voltage X average current yields a physically meaningless figure.
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AA6CJ
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« Reply #319 on: February 28, 2016, 05:13:19 PM »


Or more meaningfully, to average power.  It would be based on a true-RMS reading RF voltmeter or ammeter, with no more than a 0.250 time constant.

I understand.  I'm not aware of such a wattmeter.  If anyone does please let me know. Thanks.

Addendum - MB-1 will work.
« Last Edit: March 02, 2016, 05:03:13 PM by AA6CJ » Logged
KM1H
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« Reply #320 on: March 03, 2016, 06:20:50 PM »

Quote
I expected this question.  All valid points.  As I understand it in the PSK31 it would be considered terrible manners and completely unnecessary to run high power.

As an absolute statement....WHY? Plus it is only for HF as at VHF thru microwave and EME they often run full bore 1500W or as much as they can get...plus or minus Roll Eyes

Granted there is a ~ 20dB advantage over CW but do you really think serious DX stations at both ends wont run 1500W or so and pick up another 10-12db or so out of the noise?

Talk about working the world on an apparently, by ear, dead band and creating your own propagation!

Let the QRP JT users have their little band segments, Im sure it is fun for that mind set. Ive already confirmed 9BDXCC with a QRP 5W on CW but it took 30 years to do it on 160. So far Ive no interest in any of the digi modes but might give it a try when the 630M ham band is authorized in the US since only 5W ERP will be allowed.

Carl
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AA6CJ
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Posts: 95




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« Reply #321 on: March 03, 2016, 07:43:30 PM »

As an absolute statement....WHY? Plus it is only for HF as at VHF thru microwave and EME they often run full bore 1500W or as much as they can get...plus or minus Roll Eyes

Granted there is a ~ 20dB advantage over CW but do you really think serious DX stations at both ends wont run 1500W or so and pick up another 10-12db or so out of the noise?

Talk about working the world on an apparently, by ear, dead band and creating your own propagation!
I confess that harbor a HF centric point of view.  When we go back to solar minimum, I'm thinking about giving the higher bands and EME a go.   Smiley
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KK4YDR
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« Reply #322 on: March 03, 2016, 10:06:51 PM »

This thread has gotten so large it is impossible to keep up with it.
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K6UJ
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« Reply #323 on: March 09, 2016, 10:07:13 AM »

This thread has gotten so large it is impossible to keep up with it.


Eric,

We are going for the longest thread award   Grin Grin Grin Grin

Bob
K6UJ
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K6CKD
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Posts: 170




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« Reply #324 on: March 10, 2016, 09:21:33 AM »

Lets go back to the old days.  Input power.  Voltage times current. That made since.  From what I see,  add about 20% to the key down SSB power and you have PEP. Why do they want to complicate things.
What was wrong with kilocycle,  why does it have to be Hertz.
Whats with the call signs.  I heard a KJ the other day,  that used to be Johnson Island.  KG used used be the Mariana Islands.  Who knows what it is now.
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N6YW
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Posts: 70




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« Reply #325 on: April 07, 2016, 08:48:35 AM »

This has been an enormously entertaining and remarkable thread. I appreciate the brain trust who
set fine examples of truth verses fantasy. Of particular note was the firm handed technical spanking
that was applied to El Brino HaRO. Perhaps he will use that as an excuse to deflate his enormous ego
and take stock of his insecurities, and who knows, MAYBE consider not being a keyboard bully as his
history on the boards so well illuminates. It's a pity he has no one to circle the wagons on his behalf.
But then, that usually happens to those who behave like that and for good reason... something that he
doubtfully will ever embrace.
Thank you for the lessons.
73 de Billy N6YW
"Life is too short for QRP"
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