# [time-nuts] Switching oscillators

Tom Miller tmiller at skylinenet.net
Mon Dec 10 02:10:17 UTC 2012

```Ok, thanks for the explanation.

Tom

----- Original Message -----
From: "Bob Camp" <lists at rtty.us>
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
Sent: Sunday, December 09, 2012 8:51 PM
Subject: Re: [time-nuts] Switching oscillators

Hi

That's one interpretation and one method of measurement. The other method is
to measure frequency shift from say one hour after power on to 24 hours
after power on. A lot depends on the requirements of the system the OCXO was
intended to be used in.

If you use the measure / power off / warmup / measure approach, you need to:

1) Define the time on before the first measure
2) Define the power off time
3) Define the warmup time

Change any of those numbers and the retrace number will be different.
Generally the temperature(s) involved are also defined. The most common case
is that all of this is done at  20 or 25C.

Bob

On Dec 9, 2012, at 8:47 PM, "Tom Miller" <tmiller at skylinenet.net> wrote:

> So if I understand it, you allow the OCXO several days of warm-up to set
> the frequency. Then when turned off for a while, then restarted. After
> some warm-up period, the retrace spec would give an indication of how
> close the frequency will be?
>
> Thanks,
> Tom
>
> ----- Original Message ----- From: "Bob Camp" <lists at rtty.us>
> To: "Discussion of precise time and frequency measurement"
> <time-nuts at febo.com>
> Sent: Sunday, December 09, 2012 7:58 PM
> Subject: Re: [time-nuts] Switching oscillators
>
>
> Hi
>
> Retrace assumes that the oscillator has some "normal" frequency that only
> moves according to the aging rate. Retrace occurs after the oscillator has
> been off power for some period. The rate of change is greater than the
> aging rate. Warmup and retrace are obviously inter-related. Warmup is
> generally described as a short term (sub 1 hour) process. Retrace is often
> looked at as a day to multiple day sort of thing.
>
> Since none of this is tightly defined, you will see various specs looking
> at the same issues a bit differently. Often those differences roll up to
> some sort of system requirement.
>
> Bob
>
>
> On Dec 9, 2012, at 7:45 PM, "Tom Miller" <tmiller at skylinenet.net> wrote:
>
>> Hi Bob,
>>
>> Can you give a good definition of retrace as it applies here?
>>
>> Thanks,
>> Tom
>>
>>
>> ----- Original Message ----- From: "Bob Camp" <lists at rtty.us>
>> To: "Discussion of precise time and frequency measurement"
>> <time-nuts at febo.com>
>> Sent: Sunday, December 09, 2012 7:24 PM
>> Subject: Re: [time-nuts] Switching oscillators
>>
>>
>> Hi
>>
>> Your TCXO will have the same sort of retrace issues as your OCXO. Past
>> some number of minutes (5,10,15…) you will always be better with a modern
>> OCXO than with a TCXO.
>>
>> Bob
>>
>> On Dec 9, 2012, at 7:05 PM, WB6BNQ <wb6bnq at cox.net> wrote:
>>
>>> Hi Joe,
>>>
>>> I think you all are not looking at this correctly.
>>>
>>> 1.    First, as has been pointed out, a TCXO will vary around till the
>>> environment it is in has returned to its nominal operating temperature.
>>>
>>> 2.    A typical TCXO is nominally spec'ed around +/- 0.5 x 10-7
>>> neighborhood.  Not a stellar number.
>>>
>>> 3.    The real spec to look at is the "RETRACE" factor of a good OCXO.
>>>
>>>   Many of the modern PCB CAN manufactures do not or are quite hazy on
>>>   this point.  Vectron, for example, on their double oven high
>>>   performance WIDGET (model DX-170) claims a warmup time of 5 minutes
>>>   to +-10ppb of final frequency, however, they also include this
>>>   cryptic statement "(1 hour reading) @ +25DEGC" on the same spec.  I
>>>   am not sure, but it suggests that they are reading the final
>>>   frequency at the one hour point after turn-on.  Taking it at face
>>>   value, it suggest that the oscillator is within +/- 1 x 10-8 at 5
>>>   minutes.  That is a whole decade better than the TCXO under any
>>>   condition.
>>>
>>>   Looking at something real like the HP 10811A/B Quartz Crystal
>>>   Oscillator, you will see they spec the retrace as "Warmup 10 min.
>>>   after turn-on within 5 X 10-9 of final value, at 25DEGC and 20 Vdc.
>>>   See Notes 1 & 2.  Notes: 1. For oscillator off-time less than 24
>>>   hours. 2. Final value is defined as frequency 24 hours after
>>>   turn-on."  Here, we are talking about two whole decades better than
>>>   the TCXO ever could be.
>>>
>>> 4.    So the real question is just what the hell are you doing at 10
>>> minutes or less that would require all this worry ? ?
>>>
>>> 5.    The real answer to your dilemma is to have some serious battery
>>> backup and if it is truly to be considered a critical necessity, then
>>> maybe you need a power generator that is automatic when the shore power
>>> drops.
>>>
>>> My two cents,
>>>
>>> Bill....WB6BNQ
>>>
>>> Joseph Gray wrote:
>>>
>>>   For my use, I don't think the switching glitch will be a concern.
>>>   Most
>>>   of the time, the equipment will be in a standby mode. There is a
>>>   high
>>>   probability that the OCXO will be in use most of the time.
>>>
>>>   I guess my original idea of simply waiting a sufficient time for the
>>>   OXCO to warm up and then switching is probably the thing to do.
>>>
>>>   Joe
>>>
>>>   On Sun, Dec 9, 2012 at 3:16 PM, Bob Camp <lists at rtty.us> wrote:
>>>> Both would need some sort of timer to drive them. Both would
>>>   disrupt the instrument when the switch took place. I know of no
>>>   "cheap / easy" ways to take care of the switching glitch. There are
>>>   fancy / expensive ways.
>>>>
>>>> Bob
>>>
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>>
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