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

[Jerry Wothe]

Tis  the third Thursday of the month, it hasn't changed in may years.

On 3/17/2016 8:06 AM, kd6xh at comcast.net wrote:
> Am I right in assuming that the club meeting is tonight?  If so, I plan to attend.
>    
> KD6XH
>
> ----- Original Message -----
>
> From: "Wes (N7WS)" <wes at triconet.org>
> To: sadxa at mailman.qth.net
> Sent: Wednesday, March 16, 2016 1:57:51 PM
> Subject: Re: [SADXA] PEP vs N Tone Average Power - Amplifier Tuning
>
> 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
>>
>> ______________________________________________________________
>>
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