[R-390] Adjusting Linearity Stack Collins PTO

Sat, 28 Dec 2002 16:00:28 -0500

Hi,

Having spent most of the last 20 years doing this sort of thing there is one
other item to worry about.

The inductance of the coil will change when you put the cover on it. It
doesn't change a lot but it will change enough to notice. I doubt that it
will have a major affect but you will see it throw things off a bit.

The bottom line is that there is no easy way to set up a PTO. The people who
built the radios still remembered that as being the worst job on the entire
line 20 years after the last radio shipped .....

    Enjoy!

        Bob Camp
        KB8TQ

----- Original Message -----
From: "Bill Smith" <[email protected]>
To: <[email protected]>
Sent: Saturday, December 28, 2002 3:09 PM
Subject: Re: [R-390] Adjusting Linearity Stack Collins PTO

> Has anyone tried this?
>
> 1.  Set up a spread sheet with a list of frequency entries every 50 kHz.
> (nominal) from 3.455-2.455 mHz
>
> 2.  Rotate the PTO from one frequency end to the other.  At mechanical 50
> kHz intervals, using a counter, document the measured PTO frequency.
>
> 3.  Remove the cover.
>
> 4.  Repeat step 2, above with the cover off.
>
> 5.  Subtract the frequency differences steps 2 and 4 for each measurement
in
> the list.  The result should be the error due to capacitance contributed
by
> the cover if this scheme is to have any merit.
>
> 6.  Add (subtract) each result obtained in step 5 to each frequency in
step
> 1.   This list becomes the calibration standard for the PTO.
>
> 7.  Calibrate (adjust) the PTO at each mechanical 50kHz stop to the
> frequencies obtained in step 6.  This is a predicted error + frequency so
> that when the cover is replaced, the error will be compensated by the
cover.
>
> 8.  Replace the cover.  If the calculated error values are correct, the
PTO
> should now be linear.  Hopefully you won't have to go through a second
> calibration cycle.
>
> 73 de Bill, AB6MT
> [email protected]
>
>
> ----- Original Message -----
> From: "Dave or Debbie Metz" <[email protected]>
> To: <[email protected]>
> Sent: Friday, December 27, 2002 3:00 PM
> Subject: Re: [R-390] Adjusting Linearity Stack Collins PTO
>
>
> > At 09:04 AM 12/27/2002 -0500, Jim M. wrote:
> > >Thanks...I found this link, and also some references to Electric Radio
> > >articles, doing a Google.com search (an amazing thig).  Note:  The PTO
> > >alignment discussions on the r390a.com page appear to discuss only the
> > >Cosmos manufactured PTO.  The linearity adjustment for Collins mfgd
PTOs
> > >is considerabily different.
> > >
> > >http://groups.yahoo.com/group/r-390/message/4718
> >
> > Jim,
> >
> > Right you are on the difference between collins and Cosmos.
> >
> > A long time ago, I tried it and had limited success on a PTO that was
out
> > 6-8 kc with a procedure that went something like this:
> >
> > Take a junker PTO and cut a slit in the inner can above the camstack
about
> > a 1/4" wide to allow you to insert a piece of insulated something to
push
> > on the cam stack just above the roller.  Then, adjust the tightening
screw
> > so that you can move the stack. First, you need to find the worst
> > offset  from end to end such that you are only going to push the stack
> down
> > to either increase or decrease the freq. ( could never quite figure out
> the
> > way to pull the stack up to go the opposite direction in frequency.)
> Then,
> > mount the pto into the receiver with only the inner slotted can and push
> > down at each 25khz increment to either raise (or lower, I cannot
> remember).
> > the freq to the desired freq. I only used the inner can with the slit.
> This
> > creates a bit of a problem because you have no rear mount so you have to
> > brace it somehow. You should "T" in a counter to measure the freq with a
> > counter. Remembering the PTO goes from 2.455--3.455 inversely as the
freq
> > is acending you need to set up a chart to know what is the desired PTO
> freq
> > @ each 25khz indicated.
> >
> > I am sorry for the lack of detail but it's been a few years and I forgot
> > the details.  I am sure there must be a better way. However, I was  not
> > able to figure a way to adjust the camstack short of pulling the PTO
> > hundreds of times with a trial and error method. I seriously doubt that
> > Collins did anything trial and error.  I am so in awe of the engineering
> of
> > this setup. What a sophisticated way to linearize a very delicate
> oscillator.
> >
> > I know that there has been a lot of talk about the PTO manufacturers
here
> > on the list but a long time ago I had a conversation with Paul Zechinno
> at
> > Mil Spec Communications, (Not Rick Mish) and he was less than
> complimentary
> > on Cosmos compared to the Collins PTO's. He had years of experience with
> > these and felt that the Cosmos was probably fine when it left the
factory
> > but would not weather the years like the Collins units in the non A
390's.
> >
> > However, bottom line: Don't do it!  If you  have a PTO  within one or
two
> > KC, you have NO problem. It never was perfect and I doubt seriously that
> > you can achieve anything better.
> >
> > 73's
> > dave
> >
> >
> >
> > _______________________________________________
> > R-390 mailing list
> > [email protected]
> > http://mailman.qth.net/mailman/listinfo/r-390
>
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