[SADXA] PEP vs N Tone Average Power - Amplifier Tuning

[Richard W. Solomon]

Back in the day when I had an Ameritron AL-1200, I would just send 
a string of dits and tune for maximum output.

Today with the Solid State Amp, it's punch and go.

Times have changed.

73, Dick, W1KSZ

-----Original Message-----
From: SADXA [mailto:sadxa-bounces at mailman.qth.net] On Behalf Of W7EXG (Bill)
Sent: Wednesday, March 16, 2016 1:45 PM
To: sadxa at mailman.qth.net
Subject: [SADXA] PEP vs N Tone Average Power - Amplifier Tuning

Hi SADXA Group.. 

If you are interested in Key Down Tuning of your Linear Amp [without frying
your output devices], you might find value in my comments below. No Pulse
Tuning required. 

Most of you are probably familiar with 2 tone SSB testing:

Key Points:  1. Two Tones of different non-harmonically related frequencies
are used as input, but with identical amplitudes.
		 2. Distortion/Linearity can be directly observed with scope
voltage (V) measurements across the load resistor (R).  
		 3. Average output Power (Pavg) is 1/2 the PEP output power
P(pep), while testing. 

NOTE: Pavg is defined by V(rms)^2/R for any waveforms, which defines the
Joule Heating of a load Resistor (R). 

At the Last SADXA meeting, I had mentioned the theoretical relationship
between P(pep), and an N tone Pavg. 

Basically:
	P(pep) = N Pavg

For example, using 4 different frequencies, but identical amplitude tones, a
1500W pep output will produce a 375W average output power. 

Most 1500W output PEP amps, can tolerate 375W key down average output power,
during the 1500W PEP Output tuning process. 

Ideally, access to a peak-reading RMS calibrated Wattmeter would be of
value, since it should measure the RMS value of the non-sinusoidal waveform
as well, and thus the correct average output power. 

NOTE: Most Watt Meters [with an AM or FM designation], are usually accurate
in measuring Pavg, for the sinusoidal waveform. However, for non-sinusoidal
voltages, these meters often determine average Value of the waveform to
determine the so-called Average Power. The DAIWA CN-101L series has the FM
designation (only in the Manual).

For the 2 tone case, the Average output Power on THIS DAIWA meter will be
40% of the PEP output power (not 50%). [2.5 Pavg] = P(pep) For the 3 tone
case, [3.75 Pavg] = P(pep) For the 4 tone case, [5 Pavg] = P(pep)

In general, a simple power test on any given wattmeter, can determine the
ratio of PEP output power vs Pavg for N input tones for that meter.  This
ratio can then be used with the meter to tune the Linear Amplifier.  

I hope someone in the SXDXA will find value in these comments. I found this
method useful, in testing my Drake L7 Linear Amp to maximum potential, after
I completed the refurbishing of this amplifier. 

Best 73s, and happy testing/tuning. 

Bill W7EXG

______________________________________________________________
SADXA Website http://www.sadxa.org

SADXA mailing list
Home: http://mailman.qth.net/mailman/listinfo/sadxa
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:SADXA at mailman.qth.net

This list hosted by: http://www.qsl.net
You can support qsl.net: http://www.qsl.net/donate.html