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Author Topic: 1500 pep output max  (Read 94833 times)
AA6CJ
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Posts: 95




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« on: December 22, 2015, 12:58:42 PM »

Hi all,
On Ssb that's a whole lot less average power out than other modes.  Has anyone tried petitioning the fcc to make it RMS or average power out?
Fred, aa6cj
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REASTON
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Posts: 61




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« Reply #1 on: December 22, 2015, 01:08:03 PM »

Hi all,
On Ssb that's a whole lot less average power out than other modes.  Has anyone tried petitioning the fcc to make it RMS or average power out?
Fred, aa6cj

I suspect some hams have but if the FCC wanted hams to have more power they would have done that when they changed the power definition to peak power decades ago.  Some hams in other countries have a lot less.  Don't complain.  The FCC might lower it if attention is directed at the power allowed now.
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W1BR
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« Reply #2 on: December 22, 2015, 01:15:40 PM »

How is peak power determined? How does it differ from "RMS" power--and what is RMS power and how is it different than average power?
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W8JX
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Posts: 13268




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« Reply #3 on: December 22, 2015, 03:02:49 PM »

Hi all,
On Ssb that's a whole lot less average power out than other modes.  Has anyone tried petitioning the fcc to make it RMS or average power out?
Fred, aa6cj

I think it is a moot point because there are a lot of hams running more than legal limit under the guise of having a amp with lots of "head room"
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Ham since 1969....  Old School 20wpm REAL Extra Class..
W1QJ
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Posts: 2980




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« Reply #4 on: December 22, 2015, 04:06:00 PM »

It's all about ERP.
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WA7PRC
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Posts: 2331


WWW

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« Reply #5 on: December 22, 2015, 05:00:15 PM »

It's all about ERP.
That would be Wyatt ERP.  Wink
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N1OD
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Posts: 76




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« Reply #6 on: December 22, 2015, 05:37:41 PM »

How is peak power determined? How does it differ from "RMS" power--and what is RMS power and how is it different than average power?


Peak power is calculated using the maximum voltage that an amplifier can deliver into a 50 ohm load.  The RMS voltage of that same power output can be found by multiplying the peak voltage by .707

If you know the RMS voltage you can find the peak voltage by multiplying the RMS voltage by 1.414

Sometimes average power is equated to RMS power, but I don't think that is technically correct.

We didn't always have peak reading measuring equipment, and the RMS voltage was what a typical analog instrument would read.

Google RMS power, or RMS voltage to see it graphically.

Does that answer your question?

Paul N1OD

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AA6CJ
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Posts: 95




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« Reply #7 on: December 22, 2015, 05:56:21 PM »

Not really.  The question is whether a petition has been attempted or not.  Appreciate the banter though.
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AA4PB
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« Reply #8 on: December 22, 2015, 06:04:18 PM »

I think what we are talking about in reference to SSB is not peak power, but peak envelope power (PEP). PEP is the power at the maximum point of the modulation envelope. The relationship of peak and RMS power (.707 and 1.414) only applies to a continuous sine wave and not to the typical voice modulation envelope of a SSB transmitter. A 100W PEP SSB transmitter has the same output at the voice peaks as a 100W CW transmitter or a 100W FM transmitter. A non-PEP wattmeter reads lower on a SSB signal because the meter can't respond fast enough to read the power at the voice peaks.

RMS power by the way, is the amount of power (in an AC waveform) that produces the same amount of heating in a resistance that an equivalent amount of DC power does. 5W DC will heat a resistor to the same temperature as 5W RMS.

On SSB average power varies with the modulation waveform and RMS doesn't really apply. The only thing you can easily measure with common instrumentation is PEP.
« Last Edit: December 22, 2015, 06:11:44 PM by AA4PB » Logged

Bob  AA4PB
Garrisonville, VA
W1BR
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Posts: 4195




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« Reply #9 on: December 22, 2015, 06:20:32 PM »

[
If you know the RMS voltage you can find the peak voltage by multiplying the RMS voltage by 1.414

Sometimes average power is equated to RMS power, but I don't think that is technically correct.

We didn't always have peak reading measuring equipment, and the RMS voltage was what a typical analog instrument would read.

Google RMS power, or RMS voltage to see it graphically.

Does that answer your question?

Paul N1OD



Nope. I can find no basis that shows "RMS" power exists...
http://www.w8ji.com/amplitude_modulation.htm
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N0GW
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Posts: 47




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« Reply #10 on: December 22, 2015, 09:23:41 PM »

Here is the sorta sideways (but reasonable) logic behind the 1500 PEP maximum power limit:

Previous limit was 1000 Watts INPUT power to the final amplifier (plate current time the plate voltage).  This was usually done in Class C for CW and AM modulation.  Remember that the peak input power of a 1000 watt class C amplifier with 100% AM plate modulation is 4000 watts (4 times the unmodulated carrier level.)

A nominal efficiency for a typical class C amplifier is about 75%.  That would mean our 1000 watt input power, 100% modulated AM transmitter would have an output Peak Envelope Power (PEP) of about 3000 watts.

OK,  here is the slightly sideways part of the subject:  Our AM transmitter is double sideband.  It was reasoned that since Single Sideband occupies half the bandwidth of an AM signal, only half the power should be needed for the same signal to noise ratio.  That would be 1500 watts PEP output.  Of course, that is not mathematically correct but we came out ahead compared with what the correct calculation would have provided.  1500 watts output PEP SSB does provide an advantage over a 3000 PEP output AM signal. 
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AA6CJ
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Posts: 95




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« Reply #11 on: December 23, 2015, 04:11:13 AM »

I think what we are talking about in reference to SSB is not peak power, but peak envelope power (PEP). PEP is the power at the maximum point of the modulation envelope. The relationship of peak and RMS power (.707 and 1.414) only applies to a continuous sine wave and not to the typical voice modulation envelope of a SSB transmitter. A 100W PEP SSB transmitter has the same output at the voice peaks as a 100W CW transmitter or a 100W FM transmitter. A non-PEP wattmeter reads lower on a SSB signal because the meter can't respond fast enough to read the power at the voice peaks

On SSB average power varies with the modulation waveform and RMS doesn't really apply. The only thing you can easily measure with common instrumentation is PEP.


Cool, this I understand.   they'd have to buy into something like a running average since the power is varying all the time.  Can't hang you hat on efficiency either because that can vary tube to tube and with by class.  I guess I should be happy that cw and rtty pep is steady and by comparison allows for sooo much more output power. (Sounds like I'm a power junkie....). I could see where a digital voice encoding scheme would help, but how would you ever get the traction for that.  I read an article about how we went from AM to SSB, but I doubt it would be as easy, and that was hard.  Probably much harder.
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KG4RUL
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WWW

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« Reply #12 on: December 23, 2015, 06:17:21 AM »

It's all about ERP.
That would be Wyatt ERP.  Wink

Earp
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SM0AOM
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Posts: 258




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« Reply #13 on: December 23, 2015, 08:38:56 AM »

Here is the sorta sideways (but reasonable) logic behind the 1500 PEP maximum power limit:

Previous limit was 1000 Watts INPUT power to the final amplifier (plate current time the plate voltage).  This was usually done in Class C for CW and AM modulation.  Remember that the peak input power of a 1000 watt class C amplifier with 100% AM plate modulation is 4000 watts (4 times the unmodulated carrier level.)

A nominal efficiency for a typical class C amplifier is about 75%.  That would mean our 1000 watt input power, 100% modulated AM transmitter would have an output Peak Envelope Power (PEP) of about 3000 watts.

OK,  here is the slightly sideways part of the subject:  Our AM transmitter is double sideband.  It was reasoned that since Single Sideband occupies half the bandwidth of an AM signal, only half the power should be needed for the same signal to noise ratio.  That would be 1500 watts PEP output.  Of course, that is not mathematically correct but we came out ahead compared with what the correct calculation would have provided.  1500 watts output PEP SSB does provide an advantage over a 3000 PEP output AM signal. 

I would say that the FCC applied some precedents from the professional world.

Since long ago, the power limits applied to smaller SSB stations in the mobile services on HF have been in the range of 1000 to 1500 W PEP,
A ship station for HF is subject to a limit of 1500W if operated on the high-seas HF bands and to 400W on the MF coastal telephony bands. 
This was in turn derived from the AM power levels common in the pre-SSB era, which usually were in the order of 300 to 500 W carrier, which could provide about 1200-2000 W PEP output at 100% modulation.

An amateur station was considered to be in "the same league" as a ship station.

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K6BRN
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Posts: 1339




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« Reply #14 on: December 23, 2015, 10:02:07 AM »

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..

This is only 1/2 s-unit improvement (relative to a single tone) with a major increase in amplifier mass and cost and major improvements needed to most antenna systems.  And the near-field RF danger will increase as will stray RF problems, so shack grounding and stand-off distances become even more critical.

Considering that some countries have a 400 watt limit (UK, Australia) and our close neighbor (Canada) at 2.25 KW - only 1/4 of an S-unit higher - we are doing OK.

Brian K6BRN
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