[time-nuts] Accuracy/drift of Garmin GPS 16 HVS 1 PPS output under invalid fix conditions...

[Attila Kinali]

On Wed, 13 Mar 2019 21:41:37 +1100
Steve Olney <t0502 at internode.on.net> wrote:

> Radio astronomy is a hobby - i.e., a source of fun - although I do 
> strive to maintain a level of scientific rigour to the best of my 
> abilities.  One of the key drivers of the fun is doing things with 
> simple systems.   I get extra pleasure in using a $20 DBTV dongle as my 
> pulsar receiver to achieve the detection of a pulsar glitch (AFAIK the 
> first time an amateur has ever done so on any pulsar).   You can pay up 
> to $8,000 or so for the best SDRs. Hence, while more sensible/serious 
> people might go the way of playing with more complex systems I am 
> motivated to do it with as simple/basic a system as possible.   Granted, 
> this approach does not always work - but when it does it greatly 
> enhances the fun factor for me.

How about adding $5-$10 and going for a Brook Shera GPSDO[1,2]?
That's probably the simplest you can build yourself and
will do very well in short term hold-over. You can simplify it with
a modern uC by using its built-in timer capture/compare unit instead
of the external counter that Brooks used. Then all you need is a suitable uC,
a DAC (can be low resolution, 12bit should be more than enough) and an OCXO
(do go as low as $5 on ebay). With that, you should be able to have a
hold-over performance better than 100ns in the order of an hour or two.

			Attila Kinali


[1] https://attila.kinali.ch/sites/default/files/u2/brooks_gpsdo_schema.png
[2] https://web.archive.org/web/20140605092139/https://www.rt66.com/~shera/index_fs.htm
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