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

Sun Mar 20 11:37:38 EDT 2016

I have a couple of RF Power Meters
(HP 436A & 438) with heads that have
been calibrated or checked against a
calibrated head. That allows me to check
the accuracy on any Power Meter, but
only on CW, not pulse.

Most Birds I check are not very good, but
the Kenwood SW-2000 is pretty accurate.

73, Dick, W1KSZ

On Sat, Mar 19, 2016 at 3:56 PM, W7EXG (Bill) <W7EXG at q.com> wrote:

> Dick,
>
> My FT2000D exhibits a 50% duty cycle with continuous dits, without
> programming.  This would be equivalent to a two tone test. In some cases,
> this may not be a sufficient reduction in the Average power for a full
> 1500W
> PEP output.
>
> Unfortunatly,  most low dollar wattmeters do not properly exhibit the
> average power for pulse or N tone tests. My DAIWA Wattmeter shows only 30%
> average power with 50% RF power duty cycle.
>
> Pulse tuning down to a 10% a duty cycle [for example - the ATP-100], can
> have this same wattmeter issue.
>
> However, if any of these wattmeters are pre-calibrated, [for a given PEP
> output, the average power ratio (error) is determined], then the inaccurate
> wattmeter can still be used for accurate amplifier tuning.
>
> I noted that even in these days, there are still many new RF amplifiers,
> that still require tuning. And then.. there are the refurbished SB200,
> SB220, Drake L7s.. etc.  But, I agree, no tuning with a solid state amp is
> nice.
>
> 73s, Bill W7EXG
>
> -----Original Message-----
> From: SADXA [mailto:sadxa-bounces at mailman.qth.net] On Behalf Of Richard W.
> Solomon
> Sent: Wednesday, March 16, 2016 3:28 PM
> To: 'Southern AZ DX Association E-Mail Reflector'
> Subject: Re: [SADXA] PEP vs N Tone Average Power - Amplifier Tuning
>
> 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
>
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