[time-nuts] Switching oscillators
Tom Miller
tmiller at skylinenet.net
Mon Dec 10 00:45:14 UTC 2012
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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