[time-nuts] Plug and play GPSDOs was:(no subject)

Hal Murray hmurray at megapathdsl.net
Tue Jun 30 13:44:35 EDT 2009

> I am not very much interested in how it is achieved, but wonder if a
> 10MHz oscillator locked to GPS is now available as "plug&play" rather
> than needing a lot of time/effort/building.

> I note the Thunderbolt units available from the Far East on ebay
> for~£80gbp. Are these really P&P - that is, just connect PSU and
> aerial and out comes 10MHz locked to GPS? Is it necessary to connect
> to a computer via the RS232 link, or is that just there if you want to
> fiddle and be clever?

You probably need a PC to set it up.  After that, it should just work all by 
itself.  The problem is that the Thunderbolt doesn't have any LEDs to tell 
you that it is or isn't happy.

The main thing you might want to monitor is the number of satellites.  If 
your antenna is in a good location, that will get boring pretty quickly.  If 
your antenna is marginal, you can watch it occasionally go into holdover when 
there aren't any satellites visible.

If you like software, you could program your favorite one-chip micro to talk 
to the serial link and blink a LED when something is wrong.

You can test the holdover stuff by disconnecting the antenna.

> If so, then this may be preferrable to running my rubidium source
> continuously. 

The rubidium doesn't need an antenna.  For the price of a Thunderbolt, you 
could get a spare rubidium.  (I'm assuming you are using Telco surplus units.)

> What I am interested in is stability, not ultiamte accuracy. 

What level of stability do you need?  What time scale?  Is an OCXO good 

The nice think about a GPSDO is the great long term stability.

These are my opinions, not necessarily my employer's.  I hate spam.

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