[time-nuts] Agilent appnote
cfmd at bredband.net
Mon Jul 25 14:19:31 EDT 2005
From: "Joseph Gray" <jgray at zianet.com>
Subject: Re: [time-nuts] Agilent appnote
Date: Mon, 25 Jul 2005 10:42:05 -0600
Message-ID: <03c301c59137$ca9d1c50$66fea8c0 at antecp4>
> > That is two methods yes (you need to distinguish between phase-delay and
> > group-delay). However, considering that he was reading AP200-3 the text
> > giving
> > the reference is:
> > +/- Systematic Error
> Magnus, your psychic ability is amazing :-) Yes, I was reading AP200-3.
Not really, I can be really friendly to a Google in a window near me, and since
that appnote was being discussed recently putting one and one together was not
that difficult. ;O)
> I'm surprised that I can't find AP174-10 at Agilent, though.
I'm doing a general digging around for HP/Agilent appnotes right now...
Let's see what pops up.
> Thanks to everyone for the helpful suggestions. I had actually done a simple
> measurement of a cable with my 5370A. I saw this method mentioned on John
> Ackerman's site. The results I came up with were a bit longer than the
> actual cable. I wasn't sure if this was due to the BNC connectors and tee
> adapter, or some error in my measurement.
> Here is what I got with the average of 100 measurements: Mean = 19.197 nS
> I calculated the mean value times C (299,792,458 m/S) and then by the
> velocity factor (Beldin RG-58AU is .66, right?). This comes out to 12.47 ft.
> The coax I was using is 12 ft long.
With those values the k-value should be .6355 which certainly is possible, but
a small time-offset would certainly skew values downwards:
k = ---
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"), so doing it backwards to get the time we would expect
a delay of 18,485 ns, so you have some 711 ps extra. That is 140 mm and I don't
think that is all measurement error, but some I would expect to be in stuff
like additional lag etc. However, the speed in cable may very well be lower.
Also, do you *really* have exactly 12 feet of cable?
> As for the phantom appnote, I would still like to see a copy. It may provide
> further insight into the process.
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