+1 on the freesd-or-linux. with say a Garmin GPS-18x or whatever
timing puck. Have an intern or junior tech tackle it as a learning
exercise. The time geeks on comp.protocols.time.ntp seem to favor
low-power Soekris hardware (http://soekris.com/) for stratum-1s. You
need RS232 serial to get decent PPS; USB introduces tons of jitter.
If you have to have something pre-integrated and soon, I'd look at Meinberg:
http://www.meinberg.de/english/products/index.htm#network_sync
Word around the campfire is that the 18x is jittery compared to the 18.
Maybe it only matters if you are super-anal.
Majdi, do you have any current info on this?
-r
Ryan Malayter <malayter@gmail.com> writes:
We have several Meinbergs, quality hardware definitely. But I really wish
they'd have hardware timestamping. And 1GE instead of 100M would also
reduce jitter further.
Right now I'm seeing offset of about 65us from our meinbergss over routed
network of several hops and delay to meinbergs ranging from 0.5ms to 8.4ms
I wonder if symmetricom does NTP timestamping in HW, or only PTP?
The 18x is much worse than the 18LVC. Thankfully I still have
2 18LVCs... but that said, given the hockey puck design, and that Randy
already has an antenna, I wouldn't recommend this approach anyway. It's
really only suitable next to a window, or in a short, wooden structure.
Also, we've got a leap second pending, and at least the
18LVCs...do not appear to handle those gracefully. Mine freaked out
pretty badly in 2008 and had to be reset and reconfigured. I've also
seen them lose their configuration (which has to be reset using a Garmin
utility.) For this reason I can't recommend running them unattended.
Does anyone have any experience with the Veracity VTN-TN?
I don't, but it looks somewhat interesting.
--msa
Yo Majdi!
Does anyone have any experience with the Veracity VTN-TN?
I don't, but it looks somewhat interesting.
No, but I highly recommend the BU-353. Chrony reports jitter of about
700 nano Sec while in my basement. So no need for an external antenna
in many cases. Not tried the new BU-353-S4, but got on on order.
RGDS
GARY
Word around the campfire is that the 18x is jittery compared to the 18.
The 18x is much worse than the 18LVC\. Thankfully I still have2 18LVCs... but that said, given the hockey puck design, and that Randy
already has an antenna, I wouldn't recommend this approach anyway. It's
really only suitable next to a window, or in a short, wooden structure.
I agree the Garmin GPS 18x LVC solution is only appropriate near a
window, or in a short wooden structure. David J. Taylor's experience
was the older GPS 18 LVC had a substantially less sensitive receiver,
so that his needed to be mounted outside, while his 18x LVC works
inside.
The area where 18x LVC underperforms the 18 LVC is the jitter of the
timing of its NMEA output relative to the leading edge of the PPS.
Configured correctly, this should matter very little, and only
transiently at startup where ntpd first uses the NMEA end-of-line
timestamp (possibly fudged to bring it closer to the top of second) to
"number the seconds" before engaging the PPS. I don't recommend
attempting to use any NMEA source without PPS. With it, I don't
understand why Majdi finds the 18x LVC much worse.
The 18x is a number of years old at this point. Newer GPS receivers
(such as the Sure GPS evaluation kits at around $30) are likely to be
much more sensitive. I've heard reports of them working in basements
and in office buildings 20 or more feet from a window.
Also, we've got a leap second pending, and at least the18LVCs...do not appear to handle those gracefully. Mine freaked out
pretty badly in 2008 and had to be reset and reconfigured. I've also
seen them lose their configuration (which has to be reset using a Garmin
utility.) For this reason I can't recommend running them unattended.
There was a bug in early firmware versions of the GPS 18x LVC that
could result in the device wedging until you either left it unpowered
long enough to drain its battery/capacitor and thereby clear its
configuration, or cracked it open to achieve the same, or (as many
did) exchanged it with Garmin for a replacement. I believe that bug
was first fixed in the 3.20 or 3.30 release, but one of those made the
NMEA timing even worse, sometimes causing NMEA sentences to continue
past the next top-of-second that could have fit easily in one second
if not so delayed. The NMEA timing was improved in the 3.70 firmware,
which I recommend all GPS 18x LVC + ntpd users upgrade to,
particularly those using 3.20 or earlier.
The change history included with the 3.70 firmware doesn't completely
align with my recollection. There's no mention of fixing the bricking
bug I mentioned. The closest likely mention is of a 3.60 fix:
Version 3.50 to 3.60
1. Fixed factory firmware flash capabilities.
It does confirm the NMEA timing fix for 3.70, on the other hand.
Cheers,
Dave Hart
Does anyone use or prefer the 5Hz version of the 18x LVC?
~Seth