[time-nuts] need recomendation for a portable 10mhz referenceoscilator

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Dec 12 17:47:15 EST 2007

Rex Moncur wrote:
> Hi Said and All
> I have been following this thread with a lot of interest because my
> application is also in portable Microwave operations with narrowband modes
> such as WSJT.  The main issue here is not so much long term frequency
> stability as one only has to find a signal in an SSB passband, but the
> short-term stability should preferably be better than a few Hz over a 46
> second transmission. A second issue as others have mentioned is that one
> needs to have a stable signal at a new location within a relatively short
> period for many rover operations (say 15 mins).
> (Note: I earlier asked a question about short term stability with my Trimble
> Min-T and this has been solved by increasing the Time constant from the
> default value of 10 seconds to 200 seconds. The short-term stability is now
> better than one part in 10^10 which is the limit to which I can measure)
> Now to my Question: I note the importance of the self survey for absolute
> time but I wonder if a self survey is important for accurate frequency where
> the absolute time is not an issue?
> There are number of things that it seems one could do to achieve frequency
> stability as fast as possible at a new location.
> 1. Run the Oven off batteries full time - this can be typically only 3 to 5
> watts - for the Mini-T or the Fury.
> 2. Record the EFC voltage at the home location and insert this in software
> as starting point at the portable location.
> 3. Insert the position information in software of the portable location as a
> staring point.
> 4. As Said suggests run a short self survey of only a few minutes.
> Now I am not sure which of any of the above points are necessary or
> important but I would be grateful for the thoughts of others.
> Regards Rex VK7MO

If you make provision for multiple power sources with preassigned
priority its not necessary to run of a battery all the time, however the
battery needs to be present as a backup when the other power supplies
are disconnected.

Achieving this without disturbing the power supply voltages when
switching between various power sources requires careful design, a
simple diode OR circuit is in general inadequate particularly if more
than 2 sources (mains, external dc, internal battery) are available,
however the required circuity need not be overly complex.



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