[ntp:questions] Re: Looking for time sync hardware supported under Linux for under $400?

Richard B. Gilbert rgilbert88 at comcast.net
Wed Jan 18 14:05:31 UTC 2006


Tim Keck wrote:

> Richard B. Gilbert wrote:
>
>> You can get an "FS Oncore" GPS Timing receiver from Synergy Systems 
>> <http://www.synergy-gps.com/>
>>
>> You should plan to purchase one with the "evaluation kit" unless you 
>> are equipped to design and produce your own circuit board.  I bought 
>> one about fourteen months ago when they were still manufactured by 
>> Motorola and paid about $200 US for it.   It comes with a power 
>> supply (wall wart) and an antenna.  I've been using it with a Sun 
>> Ultra 10 running Solaris 8.   It generally synchronizes within a 
>> millisecond or less.
>> sunblok_$ ntpq -p
>>     remote           refid      st t when poll reach   delay   
>> offset  jitter
>> ============================================================================== 
>>
>> *GPS_ONCORE(0)   .GPS.            0 l    4   16  377    0.000    
>> 0.001   0.001
>>
>> There are other GPS receivers that will work quite nicely; one sells 
>> for around $85 US.   Be certain to get one with a serial (RS-232) 
>> interface (the USB interface does not work well in timing 
>> applications).  Also be certain to get a receiver designed for timing 
>> applications.  Many GPS receivers are designed for navigation and it 
>> is generally not possible for a receiver to do both timing and 
>> navigation well.
>>
>
> Maybe I'm confused, but aren't the delay, offset, and jitter in 
> milliseconds, indicating (here) 1 microsecond offset and jitter?
> Tim Keck

Your absolutely right.   You are seeing it at its very best.

sunblok_$ ntpq -p
     remote           refid      st t when poll reach   delay   offset  
jitter
==============================================================================
xGPS_ONCORE(0)   .GPS.            0 l   10   16  377    0.000  -198.45 
128.901
sunblok_$ uptime
  8:56am  up 14 min(s),  1 user,  load average: 0.00, 0.05, 0.10

and there you have it at something near its very worst!   We had a power 
outrage at about 6:30 AM EST and the system has not been up very long.
sunblok_$ ntpq -p
     remote           refid      st t when poll reach   delay   offset  
jitter
==============================================================================
xGPS_ONCORE(0)   .GPS.            0 l    5   16  377    0.000  -61.949  
40.343
sunblok_$ uptime
  8:59am  up 17 min(s),  1 user,  load average: 0.00, 0.03, 0.09
sunblok_$ ntpq -p
     remote           refid      st t when poll reach   delay   offset  
jitter
==============================================================================
*GPS_ONCORE(0)   .GPS.            0 l    -   16  377    0.000   -4.811  
22.622
sunblok_$ uptime
  9:02am  up 20 min(s),  1 user,  load average: 0.00, 0.02, 0.07




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