[time-nuts] Discipline a rubidium driven net4501 with a Garmin LVC 18?

ernieperes at aol.com ernieperes at aol.com
Fri Oct 15 19:26:43 UTC 2010


Hi Jason,

Have a look on ebay.....280567398921.....
quite good TCXO.

Rgds Ernie.







-----Original Message-----
From: Jason Rabel <jason at extremeoverclocking.com>
To: time-nuts at febo.com
Sent: Fri, Oct 15, 2010 9:10 pm
Subject: Re: [time-nuts] Discipline a rubidium driven net4501 with a Garmin LVC 18?


Nothing wrong with wanting to use a Rb as the clock source for the board. I 
almost* decided to go that route since I had a spare
PRO sitting around. But I realized that I would never need that long of 
old-over so it would kind of be a waste. I've been looking
t some cheap ($20 USD) 1PPM TCXO on ebay... Which would be a decent upgrade 
rom the stock crystal rated at 50PPM.
> Furthermore I'd like to get a 1PPS input from GPS as others already did. 
 However, I would like to use one of these Garmin GPS 18 LVC units (as on 
 http://time.qnan.org/) that usually work fine and provide a 1PPS signal 
 together with a NMEA output and connect it to the net4501 internal 
 serial port instead of the FatPPS (as John did: 
 http://www.febo.com/pages/soekris/). Is there a way to get 
 Poul-Hennings`s NTPns working with the GPS 18 as a PPS source?
I'm not 100% sure, but I *think* there is a basic PPS driver with NTPns? On my 
ox I set the course time on boot-up via ntpdate,
hen when NTPns starts it has something decent to work with (if the time is too 
ar off I think it throws an alarm).
You can get Motorola Oncore UT+ or even M12+T receivers on eBay relatively 
heap. With a little effort they *will* fix inside the
oekris box so you can just have a connector on the back for your antenna. The 
T+ receivers *will* work with NTPns.
You can checkout my first build here:
ttp://www.extremeoverclocking.com/articles/howto/Building_S1_NTP_Server_1.html
> Is there any specific reason why a 1PPS signal from another source (like 
 a Thunderbolt GPS disciplined clock) together with a FatPPS board would 
 give better results as my Garmin approach?
I *think* the PPS output from a Thunderbolt is not the raw GPS PPS but rather a 
eterministic one? Someone will have to verify /
ebunk that though. However you are also kind of doubling up on the oscillators 
ince when a Thunderbolt looses signal it will
lywheel off it's internal OCXO.
I have a pre-built image of NanoBSD w/NTPns (and I think regular NTP is on there 
oo) that I did a while back, feel free to give it
 whirl:
http://www.rabel.org/ntpns/ntpns_NanoBSD_7.tar.bz2
You might have to change some of the startup paramaters & ntpns configurations 
epending on how you wire up everything to the GPIO
ins and whatnot.

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