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Mon Mar 10 20:03:53 EDT 2008


receivers are working good enough or marginally. I passive split the antenna
line four ways. The Lucent units lock to it with about 34~45 C/N readings.
But my Z3801A has some other issue now that I've replaced the UT+. It hasn't
locked and gives recurring "UTC receiver timeout" messages on GPScon. The
previous UT+ receiver was somewhat lightning damaged and would only lock to
one or two satellites for a few hours a day, but at least it was
communicating.

It may just be a comm issue between the Z3801A motherboard and my present
UT+, since the Z3801A motherboard does answer back with serial number etc to
GPScon. So I know the baud rate at that level is communicating between PC
and Z3801A. The UT+ is a used one from one of the Lucent RFTGm units. So
maybe there's a difference in the way they were setup. The UT+'s are 2000
vintage Synergy R5122U1112 to Lucent with V2.2 firmware and no battery.

I actually have collected enough damaged UT+ boards (from the lightning
prone place I previously worked) that I should build up an NMEA test fixture
to verify they work outside the systems they normally reside in, and that
all the parameters are set correctly. Then I can try to resurrect a few. The
M1501 LNA chips are usually what goes. And I have some ideas I want to try,
to dead bug in a MMIC fix for that obsoleted LNA chip.

Charles Osborne
K4CSO, EM74wa
Duluth, GA
----- Original Message ----- 
From: "Bill Hawkins" <bill at iaxs.net>
To: "'Discussion of precise time and frequency measurement'"
<time-nuts at febo.com>
Sent: Friday, March 28, 2008 9:09 PM
Subject: Re: [time-nuts] Racal-Dana 1992 switches


Charles S. Osborne said, in part,

"Now the real question is... is there a clever way to make the Racal
1992 readout the difference in µHz between two GPS disciplined
oscillators? My only other counter, an HP5384A, is offscale at 10.000
000.000 MHz . I'm referencing the counter with one Lucent RFTG-m-XO and
clocking a Lucent RFTGm-II-XO. Things are working well enough to be
beyond my counter's ability to see any jitter. The Racal says nanosecond
time interval counter, so I bet there's a way to subtract and increase
the resolution similar to an HP53131?"

Haven't seen the answer on this list, so perhaps it occurred privately.

The Racal 1992 is able to read the phase error between two 10 MHz
signals (A and B) in degrees. I have done this with the outputs of two
3801s, which are the only pair of frequency sources that I have. This
would be sub-nanosecond accuracy except that the display shows 3-10
degrees of jitter (difference between two successive readings). This,
however, is only 10E-9. Most people on this list are investigating areas
at least two orders of magnitude lower.

I find that the phase method gives me comparative drift errors soon
enough. An hour gets you near 10E-12. Others require measurement
intervals much shorter than that, but the phase angle method is more
than adequate for time errors that humans will notice. A drift of one
second per year is on the order of 10E-8.

It all depends on your reason for pursuing accurate time/frequency
measurement.

Bill Hawkins





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