On Thu, 26 Jan 2006 22:45:57 -0500, Straydog wrote:



On Thu, 26 Jan 2006, Gary Schafer wrote:

On Thu, 26 Jan 2006 19:26:21 -0500, Straydog wrote:



The PEAK ENVELOPE POWER output will be 4 times the unmodulated output.
Re-read the deffinition of PEP which you deleted.

Yeah, I read it. Some of us have heard the rumor that the FCC has lawyers
write its material, not engineers. I wasn't too impressed with that
definition, by the way.

Well then if you don't believe anyone you should go and look it up for
yourself. You will find that same deffinition in the ARRL handbook. Oh
I forgot you don't believe what is in there either. Then try some of
the Collins Radio SSB handbooks. Maybe Art Collins didn't know what he
was talking about either? How about in the IEEE handbook.

Keep in mind when trying to understand PEP that there is no peak power
involved. It is all average power.

Also when calculating side band power and carrier power that is all
average power too. Forget about peak power.

Once you understand how this works then you can work from there to
figure out the rest.

I have eliminated all the other stuff as you seem to be going round
and round only for the sake of arguing and not for understanding.

I'm sorry but how you can write a sentence, above, like "Keep in mind when
trying to understand PEP that there is no peak power involved" when you
use "PEP" and "peak power" in the same sentence and say something that
sounds like "its there but it isn't there."

Let me explain: There is peak envelope power and there is peak power.
Peak power is seldom used. Peak power is the instantaneous power at
the very peak of the voltage and current. You will see peak currents
discussed in tube manuals often.

Our 100 watt carrier output transmitter with no modulation is 100
watts average power as we talked about before. The actual peak power
is 200 watts output. (nothing to do with modulation right now) This is
found by multiplying the 70.7 volts RMS output voltage by 1.414 to
find peak voltage. That gives us 100 volts peak. Divide that by 50
ohms and we have 200 watts peak output power. Note that peak power is
2x average power with a sin wave.

PEP
Peak envelope power does NOT involve peak power as above. It only
deals with AVERAGE power.
Remember the definition of PEP: The AVERAGE power out at the crest of
the modulation waveform.
(perhaps the "peak" in peak envelope power is a misnomer)

The modulation voltages, that we use to calculate PEP, in each side
band are also RMS voltages, they are not peak voltages.
In the figures below are typical voltages present in the signals at
the output of an AM transmitter modulated 100%. I gave these same
figures in another post.

100 watts into 50 ohms = 70.7 volts (carrier)
25 watts into 50 ohms = 35.35 volts (side band)
25 watts into 50 ohms = 35.35 volts (side band)
Total voltage = 141.4 volts (which is 2 x carrier
voltage)

141.4 x 141.4 = 20000 / 50 = 400 watts PEP. This takes care of our
PEP power.

The amount of voltage that you see on a scope when looking at this
same modulated signal, if we actually measure them with the scope,
will be peak to peak voltage as that is what the scope sees.

So measuring the composite signal voltage on the scope it will show
400 volts peak to peak. Take ½ that to find peak voltage and you have
200 volts peak. To find RMS voltage multiply that by .707 and that
will give you 141.4 RMS volts. This is what is used to calculate PEP.

73
Gary K4FMX