Ah ha! That explains the changing numbers I see on the 5370B (jitter), and explains why I see no change on the scope other than the jitter. Reading the manual, I don't see any clear explanation like what you just gave me. I see my mistake in manual interpretation but not until after reading your reply. Thank you.
-Bob On Sat, Sep 19, 2009 at 5:18 PM, Bruce Griffiths <bruce.griffi...@xtra.co.nz > wrote: > Bob > > Robert Darlington wrote: > > Hello all, > > > > I'm trying to adjust the time between the leading edge of the PPS square > > wave and the 10MHz zero crossing outputs on a Trimble Thunderbolt. The > > manual seems to indicate the cable delay compensation setting will do > this. > > > No, it doesnt. > This only adjusts the timing of the output PPS signal with respect to > the GPS time as seen by the receiver. > It is only intended to compensate for delay in the cable (and > potentially the active antenna group delay) between the antenna and the > receiver. > The PPS output is synchronous with the 10MHz signal and the delay from > the preceding zero crossing of the 10Mhz signal to the leading PPS edge > cannot be altered. > The PPS signal has considerable jitter (~300ps rms ) with respect to the > 10MHz signal zero crossing. > > As I understand things, this is also called the "PPS Offset" in the > manual. > > I've changed this from 58ns to -58ns with no visible change over the > course > > of a 12 hour period on a scope. My test setup is using an old Tek TDS > 210 > > scope triggering on the PPS on channel 1 through a 50 ohm terminator, > > trigger set to 400mV and horizontal position adjusted so that 400mV > crosses > > the center vertical graticule marking. Channel 2 is attached to the > 10MHz > > signal through another pass-through 50 ohm terminator. What I see on the > > screen looks like 15ns delay between the triggered PPS signal and the > zero > > crossing 10MHz signal. My 5370B shows 18ns delay between them when the > > start input level is set for 400mV. > > > > The manual indicates that it could take a while to see a change, but how > > long is a while? My tbolt has default settings for everything except the > > PPS Offset value (again, now sitting at -58ns). I expected to at least > see > > some change over the course of 12 hours or so, but I get nothing. Am I > > completely misunderstanding something? I accidentally cycled the power > > after making the settings change after the tbolt was up for a couple of > > months. I learned to not use a normal serial cable with an APC ups, it > cut > > the power on the UPS immediately upon plugging it into the back of my PC! > > Settings were verified after power was brought back up. Total downtime > was > > perhaps 10 seconds, but that was enough for it to lose almanac data. > > > > > > Thanks, > > Bob, N3XKB > > > > Bruce > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.