[R-390] Calibrator tone every 90 Khz

[Bob Camp]

Hi

Oddly enough since the divider is also an oscillator a 100 KHz crystal 
will give you 100 KHz markers. The multivibrator is still timed by it's 
R-C circuit and it will lock lock directly to a 100 KHz input if that's 
what you give it. It will also probably do strange things like lock up 
at 100 KHz with a 333.3333 KHz input.

Truly and almost unbelievable is the ability to be driven in KHz and 
put out in KC. It is also rumored that the circuit can be driven with 
KC and it will put out KHz ....

	Take Care!

		Bob Camp
		KB8TQ


On Jul 8, 2004, at 7:44 PM, Michael Murphy wrote:

> 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
>>> _______________________________________________
>>> R-390 mailing list
>>> R-390 at mailman.qth.net
>>> http://mailman.qth.net/mailman/listinfo/r-390
>>>
>>
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>