[ntp:questions] NMEA ref.clock better than my ISP's timeserver?

David Lord snews at lordynet.org
Fri Jun 12 17:22:34 UTC 2009


David J Taylor wrote:
> David Lord wrote:
> []
>>> I think you're needlessly overcomplicating the PPS signal.  I have
>>> the GPS 18LVC feeding /two/ parallel RS-232 interfaces, /and/ a
>>> low-current LED, so for a 30m length I think you would get away with
>>> a simple wire connection.  However, have fun with the soldering iron!
>>
>> Are you getting better than 10us offsets though? :-)
> 
> No, but I'm using Windows which is known to be not as good as FreeBSD.
> 
>> I've no idea how much signal degradation there would be using
>> utp for pps and will both put it on spice and keep the spare
>> pair in cable free to give it a try.
> 
> I'd be interested to know the results.

I'll put up some link but gps pc isn't lan connected until I
move it back and put in the extension. So far as I can see the
Garmin hasn't lost being valid source so I'm now tempted to try
out of back window with only short cable to servers.

.....

>> That's another project, putting the servers in a cupboard
>> with temperature control. Alternative of locating the crystals
>> and fitting heater is also a possibility. Cupboard idea has
>> advantage of cutting down noise and will help keep the pcs
>> from overheating.

> Cupboard keeps the PCs from overheating?  Doesn't it restrict air flow? 
> If you add air conditioning to the cupboard, a little noisy and power 
> hungry?  I would try and either go for a low-power PC (perhaps Intel 
> atom based, perhaps flash-disk), or cut down the power consumed by the 
> PC and try to keep the load constant.  Turn down the clock in the BIOS, 
> remove or disconnect the power from unwanted devices (CD/DVD drives), 
> use "green" HDs etc. etc.

Cupboard will have a quiet fan pushing a good air flow over some
cooling fins from an ex dehumidifier. The eventual servers are
600MHz VIA C3 but they don't like 30C temperatures as happened
couple of days last year. All my servers seem to be around 40-50W
but that's probably due to non low power psus as a mate has his
target < 25W but it's cost him.

> All way over the top for time-keeping "better than your ISP", of course!
> <G>

ADSL is pretty bad for ntp from my experience and faster means
worse. So yes, OTT and as mentioned before it's more important to
have  servers in sync than be spot on UTC and if I could get MSF
or DCF reliably that would be ok. I already know ground floor has
embedded steel mesh and suspect this may be case for some walls.
GPS gives much more than I need for ntp but I was also after a
good frequency reference and the gps with 10kHz out seem to be
no longer available.

David




More information about the questions mailing list