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

Christian C. Gruber cg at chilia.com
Fri Oct 15 12:45:34 UTC 2010


out of curiosity I want to build a ntp timeserver. I can remember some 
epxerimets I carried out with a DCF77 receiver and a Cobalt Qube years 
ago, however this never really worked out.

My plan is to buy a  soekris net4501 
(http://soekris.eu/shop/net4501/net4501_30_board_only_en.html) and 
modify it to use a 10MHz signal from a rubidium source via a clock-block 
(http://www.tapr.org/kits_clock-block.html). I read that a rubidium 
source is not really necessary, but since I'm a chemist I'd like to have 
something "atomic" in there that keeps my time when the GPS satellites 
drop from the sky. I found some tested rubidium sources at 
http://www.tenmhz.com/LPRO.htm, does anyone have experience with this 
seller? Are these units better than the one from China sold on eBay?

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?

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?

Altogether, this would cost about 450EUR [129EUR (net4501) + 49EUR 
(clock-block) + 176EUR (rubidium standard) + 100EUR (used Garmin GPS 18 
LVC)] excl. shipping and small stuff for a rather good time server, what 
do you think?

Best regards and thanks for your help,

Christian C. Gruber
cg at chilia.com

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