+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 -- RPM
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:
+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
-- RPM
On Tue, Jun 26, 2012 at 04:33:35PM -0400, Robert E. Seastrom wrote:
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 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 --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701 gem@rellim.com Tel:+1(541)382-8588
On Tue, Jun 26, 2012 at 9:11 PM, Majdi S. Abbas <msa@latt.net> wrote:
On Tue, Jun 26, 2012 at 04:33:35PM -0400, Robert E. Seastrom wrote:
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 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.
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 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.
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
On 6/26/12 2:34 PM, Dave Hart wrote:
On Tue, Jun 26, 2012 at 9:11 PM, Majdi S. Abbas <msa@latt.net> wrote:
On Tue, Jun 26, 2012 at 04:33:35PM -0400, Robert E. Seastrom wrote:
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 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.
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.
Does anyone use or prefer the 5Hz version of the 18x LVC? ~Seth
On (2012-06-26 15:05 -0500), Ryan Malayter wrote:
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
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? -- ++ytti
participants (7)
-
Dave Hart -
Gary E. Miller -
Majdi S. Abbas -
Robert E. Seastrom -
Ryan Malayter -
Saku Ytti -
Seth Mattinen