In message <42E5296C.6090709@bellsouth.net>, Brian Kirby writes: >You may have a "bias" error. Try connecting 1 PPS to the start input >and stop input via equal length of bnc barrels or two very short >pieces of matched length cable. Run your measurements again - you mave >have to subtract the "bias" from your measurements to get a true reading. If this is a 5370B there is an easier way: Use TI+/- mode, and measure first from start to stop, then from stop to start and take the average. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.

> You may have a "bias" error. Try connecting 1 PPS to the start input > and stop input via equal length of bnc barrels or two very short > pieces of matched length cable. Run your measurements again - you mave > have to subtract the "bias" from your measurements to get a true reading. > > Bria - N4FMN I'll try that and see what happens.

> If this is a 5370B there is an easier way: Use TI+/- mode, and > measure first from start to stop, then from stop to start and take > the average. > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 I have a 5370A, but is seems to have the same controls as the "B", so I'll try your suggestion.

From: "John Miles" <jmiles@pop.net> Subject: RE: [time-nuts] Agilent appnote Date: Mon, 25 Jul 2005 11:30:15 -0700 Message-ID: <PKEGJHPHLLBACEOICCBJOEFNEBAA.jmiles@pop.net> John, > Also... it might seem obvious, but check your 5370's reference levels to > make sure they're both 0.00. I don't remember which button calls up those > settings to the display, but if they don't match exactly (and/or your 5370 > is not in calibration), the Start and Stop channels will trigger at > different phases of the signal. > > > Belden RG-58A/U 50 Ohm is 0.66 (where as the 52 Ohm is 0.73 and > > 53.5 Ohm is > > 0.75, all is "RG58A/U") > > Is this genuine Belden cable, or whatever was on sale at Radio Shack last > week? It does make a difference. :) The above numbers all came from Beldens catalogue on the web, and whatever Radio Shack or its local equalent is having a sale on can indeed vary from this. Basically, with cables you need to know exactly what cable it is to beleive the specs, and beyond that we have manufacture variations (they only give a mean value anyway), effect of handling etc. Propper measuring is surely needed. If we really care, we should also take the rise-time of the cable into acount, so that we could combine the cables rise-time with the signal rise-time and also the counter input channels rise-time and compensate for the effective risetime if we do not measure that separately. HP has a nice little patent on calibration of time interval counters. Much recommended reading. Cheers, Magnus