[R-390] Calibrator tone every 90 Khz

[Michael Murphy]

Harold,

I screwed up: the crystal is actually a 200 kc job, not 100 kc. The
multivibrator is a divide by two afair much like a flip flop circuit, and
thus it produces the square wave and dirty little 100 kc harmonics. If you
stick a 100 kc crystal in you may get 50 kc markers!

Mike WB2UID

----- Original Message -----
From: "Bob Camp" <ham at cq.nu>
To: <mjmurphy45 at comcast.net>
Cc: "R-390" <R-390 at mailman.qth.net>
Sent: Thursday, July 08, 2004 6:36 PM
Subject: Re: [R-390] Calibrator tone every 90 Khz


> Hi
>
> That's a little far for the crystal to have drifted. I suspect that the
> multi vibrator circuit has a carbon comp resistor in it that has
> shifted value.
>
> Here's how to figure out if it's the crystal:
>
> Crystals are pretty tough to tune very far at all. Fortunately they
> rarely drift further than you can tune them. A very wide tune range
> circuit will pull a crystal 0.25 % of it's frequency. When you do this
> the stability of the oscillator is degraded quite a bit. For stable
> operation you rarely see them pulled more than about 0.0025%. Note that
> in your case the percentages refer to the 100 KHz frequency. A 10 KHz
> shift is 10%, way more than the crystal can move without being
> physically damaged.
>
> R-C circuits like the one in the mulitivibrator on the other hand can
> tune all over the place. That's why you see things like the HP 200
> series audio oscillators using R-C circuits to set up their frequency.
> They trade off stability for a wide tune range. At audio you never
> notice the stability, but at RF you would be bothered by it quite a
> bit.
>
> The manuals are generally pretty good at describing what is going on in
> the radio, but here's how the two gizmos work together:
>
> The multi vibrator runs as a frequency that is close to 100 KHz, but
> not quite on. The crystal oscillator runs at a higher frequency. When a
> pulse comes along out of the crystal oscillator *and* the multivibrator
> is just about to go from one cycle to the next the crystal oscillator
> pulse makes the multivibrator cycle. The net result is that you can
> divide frequency this way. The technical term for all this is an
> injection locked divider.  Back before digital IC's this was pretty
> common.
>
> I don't know if that helps or not but I have to post a certain number
> messages in threads that do not involve or mention certain words or I'm
> back in the penalty box .... hhmmm I wonder if penalty box is one of
> the words ....
>
> Take Care
>
> Bob Camp
> KB8TQ
>
>
>
> On Jul 8, 2004, at 12:22 AM, hdalexander at att.net wrote:
>
> > Hi All
> >
> > I have a Motorola R-390(non-A). The calibrator makes a tone
> > approximately every 90 Khz., not every 100 Khz.. For example: 14000,
> > 14090, 14180,14270, 14360. Do any of you have any words of wisdom for
> > me? Thank you in advance for any help.
> >
> > Harold Alexander
> > Modesto, CA
> > _______________________________________________
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> > http://mailman.qth.net/mailman/listinfo/r-390
> >
>
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