Alexander Sack wrote:
On Tue, Dec 8, 2009 at 3:43 PM, Bruce Griffiths
<[email protected]> wrote:
Alexander Sack wrote:
On Tue, Dec 8, 2009 at 3:01 AM, Robert Atkinson<[email protected]>
wrote:
Hi Alexander,
Welcome to the list.
Another professional option is the Trimble Accutime Gold.
http://www.trimble.com/timing/ The older Accutime 2000 and Palisade turn up
on ebay. A desk top box is the CNS Clock II
http://www.cnssys.com/cnsclock/CNSClockII.php cost about $3000 complete.
Some idea on if you want new / professional or used / amateur and if you
are a keen constructor would allow more targeted advice.
Thanks Robert!
Yeah I didn't really specify price or performance metrics in my
request. I think I should document this stuff and write up a
beginner's FAQ (I didn't see anything on LeapSecond.com).
Alright, the reason WHY I didn't actually specify much is because I
really don't know WHAT to look for. I found out today that the
rinky-dinky Endrun Technologies Cf/Ct receivers are 1k each (GPS and
CDMA variants)! I was kinda shocked because there ain't much to these
units AFAIK. So I want to step back for a second (pun intended?) and
ask everyone, WHAT SHOULD I BE LOOKING FOR? Say I want nanosecond
accuracy with respect to the PPS rising edge to absolute UTC....I know
that for sure. My target system is FreeBSD though I would like to use
something with Snow Leopard as well (even if that's just ntpd synced
locally to the FreeBSD box). I am interested in running NanoBSD on a
stand alone system.
As for as assembly, I'm open, though I haven't soldered anything since
undergraduate engineering school in a lab. I am a software guy by
trade.
Another issue is what governs the price of these units? I'd like to
think its not going to be like the audio industry.
Hope that helps,
-aps
Alexander
If you want the best performance possible from nanobsd then using an M12M or
M12+T is advisable.
In this case hardware timestamping (with a resolution of about 100ns) of the
PPS signal is used together with a customised version of the driver created
by Poul-Henning Kamp.
The cheapest option would be to obtain used M12+T timing receiver boards.
however using these would entail constructing a board with a TTL/CMOS to
RS232 transceiver and adding a 50 ohm driver for the PPS signal (required
for highest time stamping precision as it avoids the delay of an RS232
driver and receiver). The only complication being that the receiver board
uses a mating connector with 1.27mm pitch rather than the more common 2.54mm
pitch connectors used by older receivers.
Ahh thanks for this info. I was gravitating toward trying to setup
something similar using phk's ntpd driver? I need to read more.
The Soekris 4501 also needs a little mechanical work to mount the second
serial port connector on the front panel.
Whilst the Greenlee punch as used by JRA:
http://www.febo.com/pages/soekris/ can be made to work there are better
(and more expensive) punches out there that incorporate alignment
features, even so the lip on the Soekris case means that the punch guide
cannot be used (without grinding it to fit). With careful alignment this
guide isnt necesaary.
Failing that its not too difficult if one has a drill press and and
suitable files to make a neat hole for the DE9 connector shell.
If one uses the standard PC 2nd serial port cable the metal plate on the
end can be removed (not much use in a Soekris 4501) and used as a template.
Of course network congestion and queueing delays add to the timing noise
seen by client machines on the network.
Right.
If one used PTP (IEEE 1588) instead of ntp then the performance can be
substantially improved if one can avoid standard network switches with their
queueing delays.
However PTP is relatively new and as yet IEEE 1588gear hasn't yet hit the
surplus market.
Usually PTP uses hardware timestamping of the relevant network packets,
however there have been some efforts at software timestamping.
Yes but in fact I would like to play with IEEE 1588 as well for work reasons!
-aps
Bruce
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