[time-nuts] Looking for advice to get a submillisecond setup

[Chris Albertson]

I'll second that.  sub-millisend timing using NTP is very easy and not
expensive.  An old Motorola timing GPS receiver can be bought for about $20
and then all you need in some kind of computer.  NTP can run on any
existing computer while it does it's normal functions.

Getting below a microsecond is MUCH harder but getting 100X better than
your millisecond level goal is cheap and easy.

I like the old Motorola Oncore series because of their price and
performance. They are very inexpensive an 50 nanosecond 1 sigma error is
typical.   But the Garmin will work too.  Use what you have.  NTP really
can't make use a nanosecond level clocks.  NTP works in microseconds.



On Thu, Feb 19, 2015 at 2:34 PM, Jim Lux <jimlux at earthlink.net> wrote:

> On 2/19/15 9:11 AM, Matt wrote:
>
>> Hi,
>>
>> My university would like to have a <1ms precise source of time to do
>> some networking experiments (measure one way propagation delays
>> etc...). So I wandered on the internet to find the best choice with a
>> budget of ~1000€ (~1100 American dollars).
>> I've been overwhelmed by the number of possibilities (atomic
>> clocks/GPS signal etc...) and as no price appear on the seller
>> websites, it's difficult to rule out options.
>>
>>
> An inexpensive GPS receiver with a 1pps output will easily get you to much
> better than 1 millisecond.  The Garmin 18 is but one choice.  It has the
> advantage that it's already packaged, as opposed to, say, one of the little
> modules designed to be attached to a Arduino.
>
> Configuring ntp to use it is just a matter of setting up the file
> properly. NTP will use the 1pps coming in on one of the modem control
> signals (DTR, DCD, RI, etc.)
>
> (I use a USB cable to get 5V to run my GPS-18x-LVC, and wire 1pps to DCD,
> pin 1 on the 9 pin connector)
>
>
> So really, it's a matter of finding a place to put your Garmin receiver
> and string a cable that's not too long to your *nix box running ntp.
>
> People have done it with a Rpi, if you want to go that route.
>
>  I also read good comments on Garmin 18 hardware but it is so cheap I
>> wonder if it precise enough.
>>
>> I wonder if we should buy a specific box or if we could not plug the
>> antenna to a linux box with gpsd/NTPd on it ?
>>
>>
> That's exactly what you want to do.
>
> http://www.satsignal.eu/ntp/FreeBSD-GPS-PPS.htm
>
> http://www.rjsystems.nl/en/2100-ntpd-garmin-gps-18-lvc-gpsd.php
>
> (everything there should work fine with the current GPS-18x-LVC, but I'm
> sure someone on the list has actually done it and can confirm.)
>
> http://www.catb.org/gpsd/gpsd-time-service-howto.html
>
>
> Yeah, the Garmin is cheap ($85 US), so you're not going to get nanosecond
> timing, just microsecond level.  Since you need milliseconds, it's plenty
> good enough.
>
>
>
>
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-- 

Chris Albertson
Redondo Beach, California