On Sat, 31 Oct 1998 14:11:15 EST wc6w@juno.com (Radio WC6W) writes:
>
>On Fri, 30 Oct 1998 02:48:15 -0500 km1h@juno.com writes: > Has there
>been anything published on a real autotune amp? I do not mean
>a
>>bandpass design such as the old Alpha's, etc. I do not want the
>>problems of the early Collins either ( I worked on the ARC-27 !!) but
>
>>how about a cross between the old and the new. Ideally it
>>would be controlled by a PC, not an on board processor..
>>Just getting ideas for the YC-156.
>
>Hi Carl, I found that RG-402 trick just as interesting when I first
>saw it.
>:-)
> I am currently involved in an update of my own ridiculous amplifier
>and I may just drop one of those coils in for the sake of science.
>
> Switching to autotune ...
> The same Hughes piece where the coil resides is fully autotuned.
>And they also used the same techniques in a number of multistage /
>multikilowatt amplifiers of the early '60's.
> The basic layout had individual tuned grid - tuned plate stages
>with each individually neutralized plus some of the higher power
>models
>employed RF feedback around the last two stages to reduce distortion.
>
> They employed a diode descriminator to sense proper tuning with the
>input coupled through a little toroid from one leg of the grid tank
>and the reference signal injected via a capacitive divider from the
>plate circuit. The theory is that when the stage is in tune there
>will be a 180 degree difference between the plate and grid signals.
>By picking off the input from one leg of the input tank you get a free
>90 degree phase shift at resonance which makes the descriminator
>output zero when the
>stage is in tune.
> There were a number of presets selected by sensing the input
>frequency to force the tuning fairly close before enabling the
>autotune servos so as to allow reasonable range & gain in the servo
>amps and also avoid the
>obvious problem of harmonic locking.
> They also have a loading comparator circuit, similar to that
>employed in a number of Collins designs ( the 30S1 comes immediately
>to mind),
>for sensing and adjusting the load capacitor via servo.
> All of these servo amplifiers were of chopper design, likely
>directly
>using the 400 Hz power as the switching rate in the airborne units.
> I think that all of these techniques can be found in the
>professional literature of the '50's if you dig deep enough! The
>only amateur reference I can recall would be in "Amateur Single
>Sideband" by Collins Radio, 1962. They describe the tuning & loading
>methodology in chapter
>4, sections 10 B & C respectively.
>
> I'm not familiar with the ARC-27... is this the same scheme?
> In my 4CX1500B linear, built around 10 years ago, I have stepper
>motors, driven by a sine drive under microprocessor control, direct
>driving the vac. variables and roller coils of the Pi-L network. I
>didn't do anything fancy with the autotune, at that time, beyond
>including about 100 presets, which were selected by the amplifier as
>the result of interrogating my Kenwood 440 to ascertain its transmit
>frequency, and then just tweaking the plate cap automatically for the
>fine tune.
> As part of the redo, which mostly concerns the software, I am
>installing the sensors to try the "true" autotune as detailed above.
>
> I did have to surmount one minor problem in using that scheme.
>Since my amplifier has a swamped grid input, I didn't have the free
>phase shift available to use the diode descriminator. Therefore, I am
>employing a modern phase comparator, using a couple of CMOS parts,
>that can directly
>resolve the grid & plate signal's phase differences.
> I will also be adding a direct frequency count to the input, in case
>I
>ever need to use the amplifier with an exciter besides the Kenwood.
>
>73 & Happy Halloween,
> Marv WC6W
That is some great info Marv...gotta save that one to the printer!
The ARC-27 was a Collins 200-400MHz airborne TX from the 50-60's era.
Select a channel from the remote head and wait a minute while all the
motors did their thing. Always in for repair! Actually it was a nice TX
when it worked correctly and some selections were very fast. Thankfully
the main unit was remoted since the noise and dials spinning was
distracting.
73 Carl KM1H
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