[time-nuts] GPS for ntp

Tom Van Baak tvb at LeapSecond.com
Fri Oct 24 15:39:03 EDT 2014

Joe, et al.

I put some info at: http://leapsecond.com/pages/reyax/

Here's what you need to know about those Reyax GPS boards:

1) These are simple, well-made, low-cost, tiny GPS boards. Four models are available, based on three u-blox chips. The prices are $14 $16 $20 $27.

2) The 3 chips are u-blox MAX-7C, NEO-7N, NEO-M8N. See http://www.u-blox.com for chip info. Board documentation:

3) The 4 boards available:

4) The only difference between the $14 RYN25AI and $16 RYN25DI is that RYN25DI adds a ±10 V RS232 transceiver. The other 3 boards have a typical "inverted" logic-level (3.3V) serial interface, suitable for uP or SBC or UART/USB interface chip.

I have no affiliation with seller "reyax" but their boards seem a step above some of the other GPS stuff on eBay. In general I gravitate to low-cost GPS receiver breakout boards with serial I/O and clean 1PPS output. It's amazing how well these integrated antenna boards work: a truly "3-pin" timing solution: power, ground, 1PPS.

Note these are not "timing receivers" in the sense of RINEX output or external clock input or position-hold with sawtooth correction. But for less demanding work, the ±20 ns level that many of these receivers offer more than enough.

5) You can also find similar boards from US sellers such as http://parallax.com/ , http://adafruit.com/ , http://sparkfun.com/

6) All of this is grossly overkill for NTP (at the 1 ms or even 1 us level). But if some of you are pushing NTP to sub-microsecond limits, cheap GPS/1PPS receivers like this are of interest.

For more details, including almost medical-grade photos of a GPS patch antenna, see:


----- Original Message ----- 
From: "Joseph Gray" <jgray at zianet.com>
To: <Brian.Inglis at systematicsw.ab.ca>; "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Thursday, October 23, 2014 9:18 PM
Subject: Re: [time-nuts] GPS for ntp

> OK, I see source of the confusion. There is a difference of "one" character
> in the two part numbers. The RYN25 has the older Ublox chipset. The RY725
> has the Neo-7N chipset. There is only a $6 difference in price. I think
> I'll get a few to play with.
> Joe Gray
> W5JG

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