[time-nuts] Suggestion for a timing GPS receiver (Trimble / Ublox / other?)

Bryan _ bpl521 at outlook.com
Fri Jan 26 15:57:24 EST 2018

Which would be the preference as timing receiver Motorola Oncore or a Trimble Resolution T ?


From: time-nuts <time-nuts-bounces at febo.com> on behalf of Pete Stephenson <pete at heypete.com>
Sent: January 26, 2018 12:48 PM
To: Paride Legovini; Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Suggestion for a timing GPS receiver (Trimble / Ublox / other?)

On 1/22/2018 4:38 PM, Paride Legovini via time-nuts wrote:
> Dear fellow nuts,
> I plan to build a decent GPS/GNSS-based Stratum 1 NTP server, and I'm
> looking for a good and possibly affordable timing GPS receiver.

As others have pointed out, NTP over the internet isn't usually more
accurate than several tens of microseconds, so you have a lot of
flexibility in the receiver you choose.

If you need something that's simple to interface, has RS-232 polarity
signals, and is generally plug-and-play, the Garmin GPS 18x LVC is a
good choice. It's robust, compact, and easy to wire to whatever device
you want: in my case, I use a USB-A male plug connected to a USB port on
my time server to provide the required 5V power and have the serial and
PPS lines connected to the server's hardware serial port.

It's not strictly a timing receiver with a position hold mode, but it
does produce a PPS output +/- 1 microsecond, and can do "position
averaging" so it doesn't drift around more than a few meters when

It can output data in either NMEA format or the Garmin binary format,
which is well-documented and supported by GPSd. Garmin's made the
receiver for many years and has generally worked out the kinks with a
bunch of firmware updates over the years.

Another alternative is the rather older Motorola Oncore UT+ receivers
one can get on eBay for about $15 USD. No longer supported by the
manufacturer and with hardware of unknown age, it might not be the best
choice for critical systems. Still, they're true timing receivers with
sawtooth correction, are easy to power with 5V, output TTL serial (so a
MAX(3)232 can easily convert the data to RS-232 polarity) and a PPS
signal, and are well-supported by NTPd. The Oncore driver for NTPd is a
bit chatty in terms of what it logs every second, but that's easy enough
to deal with. They're cheap enough to get a few to play with.


Pete Stephenson
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