David said:
> I have directional couplers in the output (already in place) and input
(not yet >made), so measuring phases of the drive relative to the output
will be simple
>using a mixer, with the input and output drive applied to the RF and LO
>ports of a mixer.
That only gives you a zero output when the phases are 90 degrees apart.
To get 180degree phase detectors is more difficult - the best method is
to sample and phase compare at LF, as in the old HP Vector Voltmeters -
at least for VHF. I question whether stepper motors are the way to go if
you aren't using a computer - a DC servo may be easier.
Generally speaking, 'tuning' should be done for plate volts and amps to
be in phase, and 'loading' for the correct ratio of plate volts to grid
volts (or cathode volts in the case of grounded grid). One way to do
this is to use diode detectors on the input and output, and with a two
tone test, adjust for a straight line on an oscilloscope - one detector
on Y, one on X, while tuning at rated output. This could be automated
with the computer...........actually writing the program is way beyond
me.
My professional experience with auto tune is that although you can do it
at HF, trying to do it on the cheap without some knowledge of the
monents of inertia and so on of all the mechanical bits makes it a bit
'guess worky', and non-optimum. It probably isn't helped by the fact
that I failed Applied Mechanics 5 times! I argued (and lost!) with the
Training Officer - I said 97% in radio was far more to the point for a
radio engineer than 33% in mechanics - he didn't agree. Doing it at VHF
could be fun!
73
Peter G3RZP
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