Bob One way of reducing the effective noise/jitter on the PPS signal when using it with the 5370 to measure the instability of a source with respect to the Thunderbolt is to use the PPS to ARM the 5370 whilst the 10MHz from the thunderbolt starts the 5370 and the source (or a frequency generated by dividing down the source under test) being compared stops the 5370. This reduces the measurement noise by an order of magnitude.
Bruce Robert Darlington wrote: > 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. > > _______________________________________________ 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.