[Collins] Interpretation of 30L-1 manual, sec. 4.7

[Dr. Gerald N. Johnson]

On Sun, 2010-02-21 at 16:21 -0800, Robert Jefferis wrote:
> Greetings all.
> 
> This afternoon I was reading 30L-1 manuals to clear memory 
> cobwebs before adjusting a unit. I happen to have the 5th 
> and 8th editions on hand. When I got to the "TUNE METER
> ADJUSTMENT", section 4.7.g., I noted what I feel is a confusion 
> factor. Once you have increased exciter drive to the point of 
> distortion onset, you should see a minimum of 450 V p-p on the 
> scope (if you use this method). The 450 V p-p minimum output 
> voltage requirement is clearly associated with the peaks of 
> the 2-tone RF waveform envelope. This would correspond to a
> minimum output requirement of 506 Watts into 50 Ohms.

The envelope is not constant at that peak value and that affects the
other instruments.
> 
> Since this check is done with 2-tone excitation, why would the 
> RMS voltage, 160 VRMS (actually 159 if you run the numbers corresponding 
> to 450 V p-p ) be stated in the manual ?

Because with a peak reading, calibrated in RMS, voltmeter such as the
HP410B typically specified for such a measurement, will read the peak,
not the heating power(RMS) or the average. And that matches the peak to
peak value on the scope.

> Since my scope can only handle 
> 400 V p-p without an external calibrated attenuator, I don't use the 
> measurement method called for. Instead, I place directional couplers 
> in the input and output lines of the amplifier to create an X-Y display 
> on the scope. I can get much more reliable detection of distortion onset. 
> I also place a wattmeter in the amp output line. My interpretation of 
> all this is that the minimum power output with 2-tone excitation at 
> distortion onset, as indicated by a wattmeter should be 506/2=206 Watts.

Depends. A peak reading meter should show 506 watts. An average reading
meter will show less, but I think more than half. Probably about 70.7%
of the peak since the envelope is a sine squared waveform.
> 
> Have I missed something?
> 
> Yes, I know that the Tuning Indicator can be problematic, but IMO, 
> it needs to be set up correctly, regardless of how you tune the amp 
> when in service.
> 
> Bob, KF6BC
> 
>