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

Rex Moncur rmoncur at bigpond.net.au
Wed Dec 12 17:09:58 EST 2007


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



We have some customers that want the unit to do only 3 to 5 minutes of Auto

Surveying for a particular mobile military application, and the resulting  
<<100ns UTC accuracy is way better than their requirement.
 
In that case the Auto Survey time is insignificant when compared to the
OCXO 
warmup time.
 
It all depends on your particular accuracy requirement.
 
bye,
Said
 
 



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