[ntp:questions] Installing more stable oscillator?

Pete Stephenson pete+usenet at heypete.com
Sun Jul 15 03:17:44 UTC 2007

In article <4698E3AF.4020402 at comcast.net>,
 "Richard B. Gilbert" <rgilbert88 at comcast.net> wrote:

> It's also possible, and far less hazardous to your computer, to use a 
> high quality oscillator as an external reference clock for NTP.  HP used 
> to make a GPS disciplined crystal oscillator, I think it was a Z3816A, 
> that was used by telephone companies and started appearing on the 
> surplus market three or four years ago.  These were much in demand by 
> amateur radio operators as a frequency standard and by time junkies as 
> NTP reference clocks.

*nods* I saw one of those on eBay the other day. Very interesting -- it 
looks like it has an ovenized crystal oscillator and a Motorola Oncore 
GPS receiver. It's got a variety of outputs, including four PPS outputs.

Expensive, but nice.

> The cheapest route I know of is to buy a Garmin GPS18LVC GPS timing 
> receiver (< $100 US) add a 5 volt power supply and a DB9 connector and 
> plug it in to a serial port.  Install NTPD with the necessary driver, 
> start it up, and wait a few minutes for it to synch up.

I was looking at that as an option, but I was concerned about GPS signal 
strength in my area due to buildings and a limited view of the sky[1]. I 
was told that the GPS 18 LVC is a generally good unit, but that it's 
antenna reception was not fantastic in areas of marginal reception.

The Motorola Oncore receivers look pretty good, as one can attach an 
active antenna, which should help out a bit with marginal signal 
strength. That, and you keep all the expensive bits inside the 
apartment. I'm debating between the GPS 18 and the Oncore, but the GPS 
18 does seem quite a bit simpler to setup as one doesn't need to worry 
about separate boards and whatnot.

How good is the GPS 18 LVC as a time source? From what I can read, the 
leading edge of the PPS pulse is within 1 microsecond of UTC, which is 
certainly more than adequate for my needs, but it's always nice to do 
better if possible. :)

[1] I live on a first-floor apartment with essentially no usable GPS 
signal from the window. There are a few locations outside where I can 
get between 50-70% view of the sky and still have the antenna be within 
about 20-30 feet of my apartment.

Pete Stephenson

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