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

[kd6xh at comcast.net]

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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