[time-nuts] Leap Second quirk, Another hanging bridge

Hal Murray hmurray at megapathdsl.net
Tue Aug 12 19:11:24 EDT 2008

>> I got the impression that the extra $50 you pay for the Garmin receiver is 
>> well spent on a well-engineered device.

> or a ublox, or a trimble, or... always check the datasheet

Does anybody have suggestions for low cost GPS units to use for timekeeping?  
No wiring preferred.

The Garmin GPS 18 is the best candidate I know of.  The LVC version includes 
PPS but requires minor soldering.

The USB version doesn't have a PPS but it works reasonably well without any 
soldering.  It's not supported by the officiall ntpd distributions, but I 
have a driver.  It's not microsecond quality, but low milliseconds.

The SiRF chipset is used in many low cost brands.  Their latest version, III, 
is much more sensitive than the Garmin GPS 18.  Most units I've seen are USB. 
 Unfortunately, the NMEA output isn't well synchronized so it isn't very good 
for timekeeping.

I took the cover off a BU-353.  There is a PPS signal on the chip set, but no 
extra wire in the cable.  It might be possible to free up the power return 
wire by using the shield.  I haven't tried it.

The Globalsat MR-350 is a RS-232 version with PPS.  It comes with a funny 
connector and is slightly more expensive.  It's easy to replace their 
connector.  I haven't done detailed tests on the PPS.  The NMEA signals are 
as crappy as all the other SiRF units.

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

More information about the time-nuts mailing list