[time-nuts] Discussion of precise time and frequency measurement
Phaysal Khan
mortal_f at yahoo.com
Thu Jul 27 20:28:56 EDT 2006
John,
At the momet I m trying to do some similar stuff. I want to compare PPS output from two different rcvrs, the reference being Leica MC500 and the subject recvr being M12. but I am having problem with my oscilloscope which is a Tektronix one with 300 MHZ range. It is not locking on to the signal and the signal keeps on sliding sideways (seems to be a triggring problem).
by the way, could you let me know what scenario have you build for comparing your signals and what instrument are u using to check the offset between the two.
Regards
Faisal
time-nuts-request at febo.com wrote:
Send time-nuts mailing list submissions to
time-nuts at febo.com
To subscribe or unsubscribe via the World Wide Web, visit
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
or, via email, send a message with subject or body 'help' to
time-nuts-request at febo.com
You can reach the person managing the list at
time-nuts-owner at febo.com
When replying, please edit your Subject line so it is more specific
than "Re: Contents of time-nuts digest..."
Today's Topics:
1. Re: time-nuts Digest, Vol 24, Issue 47 (SAIDJACK at aol.com)
2. CDMA time synch problem in Salt Lake City, UT (Dave Andersen)
3. Leap second letters (Bill Hawkins)
4. Re: HP 5370A manual (John Day)
5. Re: GPS jamming (Robert Atkinson)
6. Loran timing experiment (John Ackermann N8UR)
7. Re: Leap second letters (Glenn)
8. Re: Leap second letters (Tom Van Baak)
----------------------------------------------------------------------
Message: 1
Date: Wed, 26 Jul 2006 21:12:12 EDT
From: SAIDJACK at aol.com
Subject: Re: [time-nuts] time-nuts Digest, Vol 24, Issue 47
To: time-nuts at febo.com
Message-ID: <556.3ec51a9.31f96cec at aol.com>
Content-Type: text/plain; charset="US-ASCII"
Hello Faisal,
a small annecdote about GPS jamming from the design of our FireFox GPS
Disciplined synthesizers:
We have a broadband synthesizer driven by a GPSDO on the same PCB. This
synthesizer would completely swamp out the GPS receiption if you set it to
1574MHz CW output, the on-board noise was so powerfull (the output of the unit can
be set from DC to 1640MHz). Our output can go up to +18dBm, millions of times
more power than the GPS signal itself...
The effect was that the M12+ receiver would just loose lock within a +-5 -
10MHz bandwidth around the GPS carrier. The receiver would show 0 sattelites
being received. As soon as you set the frequency outside of this band,
everything was fine.
We improved this by putting the GPS board into a metal shield. So the effect
of noise generated inside the enclosure was greatly mitigated.
But the CW power radiated by the BNC connector itself on the unit is still
enough to find its way to the antenna 10 meters away and about 3m above it, and
swamp the signal!
Putting a small paperclip into the BNC RF output connector at +18dBm at
1574MHz would probably cause a couple of blocks in our neighbourhood to loose GPS
lock :)
Never tried this and never will of course.
bye,
Said
------------------------------
Message: 2
Date: Wed, 26 Jul 2006 21:14:34 -0400
From: Dave Andersen
Subject: [time-nuts] CDMA time synch problem in Salt Lake City, UT
To: Discussion of precise time and frequency measurement
Message-ID: <44C8137A.40303 at cs.cmu.edu>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
I've sent this to EndRun tech support, but since they're not around at
the moment, figured I'd run a quick check with people on the list. I
don't really expect an "oh, here's your problem", but I'd love one if
someone happens to know!
I have a somewhat older Praecis Ct (CDMA cellular time receiver) that
seems to be having either general problems or leap second problems, or
is locking itself to a bad CDMA station. I'm a little baffled.
ntpdc> pe
remote local st poll reach delay offset disp
=======================================================================
*clock.xmission. 155.98.35.100 1 64 377 0.03848 0.664292 0.00499
=ops.emulab.net 155.98.35.100 2 64 377 0.00032 0.629554 0.00421
=GPS_PALISADE(0) 127.0.0.1 0 16 377 0.00000 0.000439 0.00023
I reset it and tried again a bit later, with more ntp servers:
=nist1.symmetric 155.98.35.100 1 64 1 0.03024 0.681881 7.93750
=clock.xmission. 155.98.35.100 1 64 1 0.03828 0.704977 7.93750
=ops.emulab.net 155.98.35.100 2 64 1 0.00037 0.683862 7.93750
*GPS_PALISADE(0) 127.0.0.1 0 16 37 0.00000 0.000297 0.43768
(top is nist1.datum.com, which I'm fairly certain is good)
Running the latest firmware from the website:
Praecis Ct FW 6010-0001-000 v 2.18 - May 25 2004 16:09:30 Praecis FPGA
6020-0001-000 v 09
The node is located in Salt Lake City, UT, at the University of Utah.
My guess, based on the other times I've seen things like this happen, is
either:
a) It's synched to a CDMA base station that's running some funky
version of the spec. This happened a while ago when some sites upgraded
to an early version of the CDMA2000 spec, for instance.
b) It's synched to a CDMA base station that's just completely lost its
clock. Last time this happened, it was a BS that was configured with
the wrong # of leap seconds (a few years ago, before the last one), but
this 0.7 second offset is just weird.
Some settings and debug info from the Ct, which probably won't make much
sense unless you've got one of these things yourself.
spstat shows:
LKD PRIB 57 212 35130 5.0 0.787
for the first, and
LKD PRIB 57 212 35128 5.8 0.029
for the second try. (I should note that there was another one in there
where we actually appeared to be off by .96 seconds.)
Settings on the Ct are:
Cal = +0.000000000
ChannelSet = NORTH AMERICA
Ctime = OFF
DSTStart = 0,0,0
DSTStop = 0,0,0
Emul = TRIMBLE
Event = ON (TRIMBLE)
Leap = 14 14
Lo = +0:00
Port = 9600,8,N,1
Respmode = TERSE
Tmode = UTC
and there are no "fudges" or other things applied in ntp.conf that would
be causing the problem, as far as I can tell.
Hardware settings are:
Auxout = Ldetb
IFDiv = 0
NDiv = 29448
Agc = 212
Agc Mode = Auto
A/D Gain = 2 (High)
CarrierLock = On
CarrierPLLType = TYPE 0
EarlyLateMode = On
decoded msg is:
TimeStamp___ Ticks Len Typ Rev MRev Sid__ Nid__ PnO SysTime___
Lp Off DST BadCrcCount
19088472 966 26 1 5 2 94 1 57 10474949728
14 -12 0 0
Leapinfo is:
CDMA system message leap second field = 14
User override settings: Override = 1, current = 14, future = 14, saved
timetag = 837977017
Current timetag = 837996007, current leap seconds = 14, current leap
state = OFF
Saved CDMA information is:
TimeStamp___ Nid__ Sid__ PN_ SNR_ AGC TCXO_ LO_ DST Leap Len
Type Rev MRev Freq_
837976990 1 94 57 5.4 213 35133 -12 0 14 26
1 5 2 PRI B
837995243 1 94 57 6.2 212 35131 -12 0 14 26
1 5 2 PRI B
Any clue would be appreciated!
-Dave
------------------------------
Message: 3
Date: Wed, 26 Jul 2006 22:16:30 -0500
From: "Bill Hawkins"
Subject: [time-nuts] Leap second letters
To: "'Discussion of precise time and frequency measurement'"
Message-ID: <000001c6b12b$0e317470$0300a8c0 at cyrus>
Content-Type: text/plain; charset="us-ascii"
"Science News" for June 24, 2006 (yes, I'm behind on some
reading) has a letters column devoted to their article,
"To Leap or Not to Leap" in the 22 April issue.
Michael Zachary of Phoenix says he wouldn't mind accumulating
3600 leap seconds before changing because that's a time zone.
Dave Heiden of Stratford, Conn, suggests that computers can
have an algorithm to compute UTC from atomic time, starting
at the new millennium.
Frederic Fallon of Bowie, MD, suggests readjusting the definition
of atomic time so that there would be as many leaps ahead as back.
Dennis McCarthy of USNO said that the definition was too embedded
in the definition of physical standards to change. Besides, there
are more leaps back as the Earth slows down.
Just thought you'd like to know...
Bill Hawkins
------------------------------
Message: 4
Date: Thu, 27 Jul 2006 02:54:55 -0400
From: John Day
Subject: Re: [time-nuts] HP 5370A manual
To: Discussion of precise time and frequency measurement
Message-ID: <7.0.1.0.0.20060727025411.01aecf28 at wordsnimages.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed
>Perhaps if you notice it appear on the Agilent site you can drop me a
>email. Then I'll remove it from my site, as I need to free up some disk
>space. But until it actually appears, I'll keep it here.
If you need the space David - both manuals are at http://nm2.org/files
John
>--
>Dr. David Kirkby
>
>_______________________________________________
>time-nuts mailing list
>time-nuts at febo.com
>https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
------------------------------
Message: 5
Date: Thu, 27 Jul 2006 08:57:48 +0100
From: "Robert Atkinson"
Subject: Re: [time-nuts] GPS jamming
To: "Discussion of precise time and frequency measurement"
Message-ID:
Content-Type: text/plain; charset="us-ascii"
Hi,
While not related to Timing systems, I personally know of two other
causes of GPS Jamming. They both relate to aviation (my background). The
first was leakage of receiver local oscillator signals from VHF
communication receivers. For example a Rx tuned to 132.525 MHz with a
10.7MHz I.F and high side local oscillator would have the L.O. at
143.225. The 11th harmonic is 1575.475.
Garmin sell a 1.575.42 MHz notch filter Part No.330-00067-00 to fit in
the antenna coax of the radio.
The second is the jamming of mobile GPS's near our local airfield. The
cause is unknown but is believed to be receiver overload caused by the
"L" band (roughly 1 to 1.4GHz) ground movement radar.
Robert G8RPI.
-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of SAIDJACK at aol.com
Sent: 27 July 2006 02:12
To: time-nuts at febo.com
Subject: Re: [time-nuts] time-nuts Digest, Vol 24, Issue 47
Hello Faisal,
a small annecdote about GPS jamming from the design of our FireFox GPS
Disciplined synthesizers:
We have a broadband synthesizer driven by a GPSDO on the same PCB. This
synthesizer would completely swamp out the GPS receiption if you set it
to
1574MHz CW output, the on-board noise was so powerfull (the output of
the unit can
be set from DC to 1640MHz). Our output can go up to +18dBm, millions of
times
more power than the GPS signal itself...
The effect was that the M12+ receiver would just loose lock within a +-5
-
10MHz bandwidth around the GPS carrier. The receiver would show 0
sattelites
being received. As soon as you set the frequency outside of this band,
everything was fine.
We improved this by putting the GPS board into a metal shield. So the
effect
of noise generated inside the enclosure was greatly mitigated.
But the CW power radiated by the BNC connector itself on the unit is
still
enough to find its way to the antenna 10 meters away and about 3m above
it, and
swamp the signal!
Putting a small paperclip into the BNC RF output connector at +18dBm at
1574MHz would probably cause a couple of blocks in our neighbourhood to
loose GPS
lock :)
Never tried this and never will of course.
bye,
Said
_______________________________________________
time-nuts mailing list
time-nuts at febo.com
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
------------------------------
Message: 6
Date: Thu, 27 Jul 2006 07:42:01 -0400
From: John Ackermann N8UR
Subject: [time-nuts] Loran timing experiment
To: Discussion of precise time and frequency measurement
Message-ID: <44C8A689.8010501 at febo.com>
Content-Type: text/plain; charset=ISO-8859-1
I'm currently running an experiment comparing the 1pps from an Austron
2100 Timing receiver to GPS (from an M12+T). If you're interested, the
results are at http://www.febo.com/time-freq/plots/loran-gps.html,
updated every 15 minutes.
I'm averaging for 100 seconds; below that the noise (mostly, I think,
from the GPS) dominates.
Oh, and FWIW, both the 2100 and the counter are getting their reference
from a 5061A that is about -2x10e-13 versus GPS.
John
------------------------------
Message: 7
Date: Thu, 27 Jul 2006 10:33:08 -0400
From: Glenn
Subject: Re: [time-nuts] Leap second letters
To: Discussion of precise time and frequency measurement
Message-ID: <44C8CEA4.4020401 at net127.com>
Content-Type: text/plain; charset=us-ascii; format=flowed
Is this article available online? Or, would someone be willing to scan it?
thanks,
glenn
Bill Hawkins wrote:
>"Science News" for June 24, 2006 (yes, I'm behind on some
>reading) has a letters column devoted to their article,
>"To Leap or Not to Leap" in the 22 April issue.
>
>
------------------------------
Message: 8
Date: Thu, 27 Jul 2006 08:22:41 -0700
From: "Tom Van Baak"
Subject: Re: [time-nuts] Leap second letters
To: "Discussion of precise time and frequency measurement"
Message-ID: <003501c6b190$818f58a0$710ff204 at computer>
Content-Type: text/plain; charset="iso-8859-1"
> Is this article available online? Or, would someone be willing to scan it?
Science News: To Leap or Not to Leap
http://www.sciencenews.org/articles/20060422/bob8.asp
/tvb
http://www.LeapSecond.com
------------------------------
_______________________________________________
time-nuts mailing list
time-nuts at febo.com
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
End of time-nuts Digest, Vol 24, Issue 49
*****************************************
---------------------------------
Do you Yahoo!?
Next-gen email? Have it all with the all-new Yahoo! Mail Beta.
More information about the time-nuts
mailing list