[time-nuts] Switching oscillators

WB6BNQ wb6bnq at cox.net
Mon Dec 10 00:05:57 UTC 2012

   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

     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

   My two cents,


   Joseph Gray wrote:

     For my use, I don't think the switching glitch will be a concern.
     of the time, the equipment will be in a standby mode. There is a
     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.


     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

     time-nuts mailing list -- time-nuts at febo.com
     To unsubscribe, go to
     and follow the instructions there.


   1. https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts

More information about the time-nuts mailing list