[time-nuts] ocxo

Sun Dec 7 19:11:53 EST 2014

Hi,

The on-board TCXO or Option 01 OCXO is either free-running with the 
calibrated DAC value or being PLL-locked to the external ref. Either of 
those two 10 MHz sources will then be synthesized into 90 MHz. However, 
the 90 MHz path has a pretty hefty filtering with crystal filter, so it 
should be able to fairly well surpress the +/- 5 MHz sidebands on the 90 
MHz carrier. There is some 10 MHz routes (10 MHz TTL and 10 MHz ECL) 
going out, where the TTL end seems to end up in the time-base end, while 
the ECL one ends up in the 1 kHz reference generator. Both seems to have 
the necessary division by 2 which cancels any 5 MHz variation out. Seems 
like on first inspection it should be relatively insensitive to 5 MHz 
doubling. What is an issue is the increased white noise, but filtering 
helps to bring some of that out.

There is several factors in the 90 MHz synthesis chain which should be 
investigated for the environmental sensitivity (such as temperature).

Cheers,
Magnus

On 11/23/2014 03:27 PM, Bob Camp wrote:
> Hi
>
> If all the “good stuff” runs on the 90 MHz, the 5 MHz issue may not be important at all. It’s just something to watch for. If you start seeing data in two groups, each one 20 ps wide and separated by maybe 200 ps, you are seeing a problem from the 5 MHz.
>
> Running the box for a while before doing a full detailed cal is a very good idea. It’s a bit warm inside and some of the stuff is temperature sensitive. You want it to reach equilibrium.
>
> Bob
>
>> On Nov 23, 2014, at 1:06 AM, Don Latham <djl at montana.com> wrote:
>>
>> Ah. Got it finally!  Doh. Just finished trying out the Morion this afternoon.
>> Electrically works very well. Used a 7812 to drop the +15 volts from the
>> option 1 ocxo, there is enough power headroom to bring the Morion up from cold
>> and run it comfortably. As you said, the control voltage for the original is
>> indeed 5 v, and can be set by the internal d/a. The output of the oscillator
>> passes through an emitter follower voltage adjuster and through a low-q filter
>> to three stages of ECL buffer and then out to the 10 MHz system bus clock.
>> Another path proceeds to a relay-switched divide by 2 to the phase detector so
>> an external 5/10 MHz source can lock the internal oscillator.
>> The external 5/10 MHz source proceeds to the phase detector thru an identical
>> buffer chain without the switched divider.  The remainder of the clock
>> circuits is a multiplier to 90 MHz.
>>
>> I'll run the autocal tomorrow and then get some jitter stats if possible. This
>> is an early specimen, s/n about 700 or so. I can imagine seldom used, and
>> sitting on standby for 20 years or so, pushing the ocxo out of tolerance.
>>
>> The saga continues; I may have to look for a 10 MHz replacement on epay, there
>> isn't room to put in an Hp, unfortunately.
>> Don
>>
>>
>>
>>
>> Bob Camp
>>> Hi
>>>
>>> At least the Morion’s I have seen have 5 MHz crystals in them rather than 10
>>> MHz. They have a 10 MHz output due to an internal doubler. Since the circuit
>>> is not perfect, there is cycle to cycle variation in the 10 MHz. It’s way more
>>> jitter (measured in picoseconds) than the oscillator has due to phase noise.
>>> My concern is that a counter might be bothered by this is some subtle way.
>>>
>>> Bob
>>>
>>>> On Nov 22, 2014, at 3:55 PM, Don Latham <djl at montana.com> wrote:
>>>>
>>>> Hi Bob: no. cobble, not double :-)  A little research has me thinking I can
>>>> easily adapt a morion. I can try it at least by starting with the morion on
>>>> an
>>>> external power supply and patching the output and control voltages in to the
>>>> sr.
>>>>
>>>> The sr620 has a control circuit which apparently accomplishes your
>>>> suggestions; they claim to use the internal oscillator for short term and
>>>> "lock" it to a supplied external source for longer term. Probably has a long
>>>> time constant on the built-in phase lock to do this.
>>>>
>>>> Anyhow, autocal calibrates everything except, guess what, the 10 mhz source.
>>>> Thats done separately.
>>>> So a bootup self check shows OK even if the frequency standard is way off.
>>>>
>>>> Onward and upward.
>>>> Don
>>>>
>>>> Bob Camp
>>>>> Hi
>>>>>
>>>>> I believe that the SR620 uses a “true” 10 MHz OCXO. I would be careful
>>>>> using a
>>>>> 5 MHz doubled to 10 OCXO. The counter may or may not be happy with
>>>>> sub-harmonic induced jitter.
>>>>>
>>>>> Best bet at the specs:
>>>>>
>>>>> +12V power
>>>>> 0-5V EFC
>>>>> Sine wave out +7dbm
>>>>>
>>>>> +/- 5x10^-9 0 to 70C
>>>>>
>>>>> Pinout - trace what you have.
>>>>>
>>>>> Bob
>>>>>
>>>>>> On Nov 21, 2014, at 6:59 PM, Don Latham <djl at montana.com> wrote:
>>>>>>
>>>>>>
>>>>>> So, I got a reasonable deal on a SR620 ho ho. Know your dealer. The ocxo
>>>>>> is
>>>>>> out of tolerance. All self tests pass with flying colors, autocal works as
>>>>>> well. So the best parts are OK.
>>>>>> Does anyone:
>>>>>> 1) have a spare Isotemp OCXO36-53 10.000 MHz  p/n 6-00051?
>>>>>> 2) know the specs, ie the input voltage/current and the control voltage
>>>>>> span
>>>>>> and direction? pinout?
>>>>>> I have some Morion mv-89's  and could easily cobble one in if it will
>>>>>> work.
>>>>>> Apparently a correct oscillator must be in place to use an external
>>>>>> source,
>>>>>> if
>>>>>> I read the manual right.
>>>>>>
>>>>>> 3) do we have a source for the schematics for the SR 620?
>>>>>>
>>>>>> The FTS 4060 is up, pumpin' and firmly locked. At least for now. That
>>>>>> dealer
>>>>>> was not lyin'
>>>>>>
>>>>>> Much thanks to all of you.
>>>>>> The adventure continues
>>>>>>
>>>>>>
>>>>>> --
>>>>>> "The power of accurate observation is commonly called cynicism by those
>>>>>> who
>>>>>> have not got it."
>>>>>> -George Bernard Shaw
>>>>>>
>>>>>> Dr. Don Latham AJ7LL
>>>>>> Six Mile Systems LLC
>>>>>> 17850 Six Mile Road
>>>>>> Huson, MT, 59846
>>>>>> mail:  POBox 404
>>>>>> Frenchtown MT 59834-0404
>>>>>> VOX 406-626-4304
>>>>>> Skype: buffler2
>>>>>> www.lightningforensics.com
>>>>>> www.sixmilesystems.com
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> time-nuts mailing list -- time-nuts at febo.com
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>>>>>
>>>>> _______________________________________________
>>>>> time-nuts mailing list -- time-nuts at febo.com
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>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> "The power of accurate observation is commonly called cynicism by those who
>>>> have not got it."
>>>> -George Bernard Shaw
>>>>
>>>> Dr. Don Latham AJ7LL
>>>> Six Mile Systems LLC
>>>> 17850 Six Mile Road
>>>> Huson, MT, 59846
>>>> mail:  POBox 404
>>>> Frenchtown MT 59834-0404
>>>> VOX 406-626-4304
>>>> Skype: buffler2
>>>> www.lightningforensics.com
>>>> www.sixmilesystems.com
>>>>
>>>>
>>>> _______________________________________________
>>>> time-nuts mailing list -- time-nuts at febo.com
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>>>
>>> _______________________________________________
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>>
>>
>> --
>> "The power of accurate observation is commonly called cynicism by those who
>> have not got it."
>> -George Bernard Shaw
>>
>> Dr. Don Latham AJ7LL
>> Six Mile Systems LLC
>> 17850 Six Mile Road
>> Huson, MT, 59846
>> mail:  POBox 404
>> Frenchtown MT 59834-0404
>> VOX 406-626-4304
>> Skype: buffler2
>> www.lightningforensics.com
>> www.sixmilesystems.com
>>
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
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