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

[Wes (N7WS)]

Good stuff.  BTW, an Elecraft K3(S) has a built-in two-tone generator.

On 3/16/2016 1:45 PM, W7EXG (Bill) wrote:
> 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
>
> ______________________________________________________________
>