[time-nuts] Discussion of precise time and frequency measurement
John Ackermann N8UR
jra at febo.com
Fri Jul 28 01:11:43 UTC 2006
Hi Faisal --
I use a time interval counter to compare 1pps signals -- the DUT goes to
the start input, and the reference (here, GPS) to the stop input. You
measure the time interval between the two, and use the change in
interval to determine noise and offset. For the LORAN experiment, I
used my HP 5370B though this application could do with a much simpler
counter. I use homebrew logging programs under Linux using GPIB to log
and process the data.
John
----
Phaysal Khan said the following on 07/27/2006 08:28 PM:
> 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
>
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> 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
> *****************************************
>
>
>
>
>
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