Re: [time-nuts] 3.0GHz Channel 3 installation in Agilent 53132A counter

[Dave Martindale]

No, the suggestion makes perfect sense.  A 12 GHz input board likely
has an internal prescaler with a division ratio that is 4 times that
of a 3 GHz input board, in order to have the main counter running at
the same internal frequency.  For example, a 3 GHz input might divide
by 32 while a 12 GHz input might divide by 128, so that both feed a
signal in the 0 to 100 MHz range to the main counter circuits.  (And
the 5 GHz input might divide by 64...)

When the firmware goes to display what the main counter measured, it
has to multiply by the prescaler ratio to obtain the original input
frequency.  If this multiply happens on the main board (e.g. in a FPGA
or CPU), it needs to be told which prescaler division ratio was used.
If the firmware thinks the 12 GHz input is installed instead of the 3
GHz input, it will multiply by 128 instead of 32, and the displayed
frequency will be 4 times the actual frequency (since the prescaler
actually divided by 32).

(The prescaler division ratios may not be 32 and 128; the actual
values don't matter.  As long as the 12 GHz option uses 4 times the
prescaler divisor of the 3 GHz option, the display error will be a
factor of 4).

- Dave

On Wed, Mar 19, 2014 at 11:26 AM, James Robbins jsrobb...@earthlink.net wrote:

 Someone suggested that maybe the new main board had been set up for the 12.5 
 or 6GHz channel 3 but was sold without that channel.  The idea was that such 
 a main board would cause a 4x reading.  To my mind this is opposite to what I 
 would think in that the division ratio for 12.5 or 6GHz would be higher than 
 the ratio for the 3.0GHz board and would result in a fraction of the 
 frequency rather than 4x frequency.
 and follow the instructions there.
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Re: [time-nuts] Measuring the accurcy of a wrist watch

[Dave Martindale]

Here is a discussion forum page that shows a commercial quartz watch 
timing machine in use:

http://omegaforums.net/threads/quartz-watches-some-information-some-may-find-interesting.5475/

The machine obviously measures the time of each second tick, either 
electrically or acoustically, because it can tell you the instantaneous 
rate over one second based on the time between ticks. In the example 
shown, the crystal is fast by 4.18 seconds/day (48 PPM) based on the 
period between most ticks, but every 60th tick has a longer period due 
to inhibition (oscillator pulse dropping), and the net rate measured 
over 60 seconds is 0.32 seconds/day (3.7 PPM).


There is a bunch of additional information about the motor drive pulses 
too.  The article explains what it means in some detail.


It seems to me that calculating the rate information should require 
nothing more than capturing the leading edge of each motor pulse and 
time stamping it, at a rate of 1 data point per second.  The motor 
information requires capturing several pulses (at a rate of a few kHz 
max.) every second.


- Dave

On 15/04/2014 09:52, Tom Van Baak wrote:

Some research has shown that there is an comparable instrument for ANALOG
quarz watches. As far as I understand it does not try to detect the quarz
frequency but detects magnetic pulses from the step motors that move the
hands of the watch.

Has anyone of you ever tried to do this in a time nuts laboratory?

Ulrich,

Yes, this works well, for both those with seconds hands (one magnetic pulse per 
second) and those with only minute/hour hands (one or two steps per minute). A 
large coil of wire is all you need. Have a look at the watch timing tools and 
sensors at http://www.bmumford.com/microset.html or 
http://www.bmumford.com/mset/modelwatch1.html

Here's an example using a magnetic sensor: http://leapsecond.com/pages/Junghans/

/tvb

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[time-nuts] GPS week number rollover finally bites Garmin GPS 45XL

[Dave Martindale]

A few days ago, I took my collection of obsolete handheld GPS
receivers outside and turned them on, to let them find themselves and
collect new almanac data.  Most of them probably hadn't been turned on
for 2 years or more.  All of them eventually acquired satellites and
started navigating.  The old single-channel 45XL took 30+ minutes for
this, the little Sony GPS-CS1 position logger needed only 30 seconds,
and the others (all Garmin 12-channel handhelds) took perhaps 5
minutes.

Once navigating, almost all of the units agreed that the date was May
22, 2014.  All except the 45XL, which insisted on a date of October 6,
1994.  Yes, exactly 1024 weeks early.

I bought the 45XL in 1996, my second GPS receiver.  It survived the
actual week number rollover in 1999 (with a correctable problem; see
below), and continued to work (as well as a single-channel receiver
ever works) for many years afterward.  Thus, the firmware was clever
enough to know that low week numbers actually dates after mid-1999,
not in early 1980.  It probably did this with a birth week embedded
in the firmware somewhere.

But the birth week appears to be 1994 or earlier, since the 45XL
looks at the current GPS week and concludes that today is in 1994, not
2014.  I doubt if there is anything to be done about this, since the
45XL predates the Garmin units with firmware in flash.  I think the
12XL was the first unit that could be updated by the factory, and
user-updatable units came later yet.

It remains to be seen what the other Garmin units (II+, eMap, eTrex)
will do as they get near 20 years old; I wouldn't be suprised to see
them start reporting incorrect dates as well.  They do have flashable
firmware, but I don't really expect Garmin to release firmware updates
for 20 year old units.

- Dave

About the 45 XL in 1999: At the actual time of the WNRO in August
1999, the 45XL was operating in my car while driving on a highway,
logging the trip.  Nothing happened at 00:00 UTC that I noticed.  I
turned the 45XL off at about 00:30 UTC (17;30 local time) when we
stopped for dinner.  On return to the car, the 45XL would not acquire
satellites, and we went without it for the rest of the trip.

Within a few days, Garmin released a fix - a PC program that
apparently used an undocumented interface command to clear the old
almanac.  (I guess the firmware did not handle week number rollover in
the almanac correctly).  But with the old almanac cleared, the 45XL
did a cold start, resumed navigating, and continued working for
another decade or more.
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Re: [time-nuts] 58503A date code problem

[Dave Martindale]

Interesting.  It was May 22 this year when I first noticed that my
Garmin 45XL was reporting a date in 1994, exactly 1024 weeks early.
That's also consistent with Garmin having used 768 weeks as their
fence for a GPS week being in the past instead of the future.

It's really the same as the International Date Line, picking an
arbitrary line that advances and retards the apparent time as you
cross it.  But the delta-time for the GPS week rollover is nearly 10
years, instead of 24 hours.

- Dave

On Sat, Jun 21, 2014 at 3:44 PM, Tom Van Baak t...@leapsecond.com wrote:
 Hi Daniel,

 What you have is a 58503A, the GPS time/frequency receiver (the 58530A is a 
 GPS bandpass filter).

 Note that today is MJD 56829. Exactly 1024 weeks (7168 days) ago was November 
 4, 1994. So this looks like a typical GPSDO week number rollover issue. It 
 shouldn't affect the time or the 1PPS or the 10 MHz. One thing to try is 
 manually setting the date using a SCPI command.

 You can check www.realhamradio.com/GPS_websites_list.htm to see if anyone 
 else has seen this on their 58503A or Z3801A receivers.

 Did you notice it happened just today, or did it start happening maybe a few 
 weeks ago?

 I ask because recently we passed the 3/4 mark in the current 1024-week (19.6 
 year) GPS cycle. Specifically, on 2014-05-04 it was 768 weeks since the last 
 rollover (1999-08-15) and 256 weeks before the next rollover (2019-03-31).

 /tvb

 - Original Message -
 From: Daniel Burch daniel.bu...@ieee.org
 To: time-nuts@febo.com
 Sent: Saturday, June 21, 2014 10:06 AM
 Subject: [time-nuts] 58503A date code problem


 Hi All,

 I have a HP/Symm 58530A that has the correct time, but date keeps
 defaulting to 1994, Nov, 4 after GPS Lock.  The pre-lock is 1996, so I do
 see a change when it locks, just to the wrong date.time is exactly
 correct and tracks.

 Any ideas?

 Thanks!

 db


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[time-nuts] Bolivian Congress building clock now runs counter-clockwise

[Dave Martindale]

The clock face has also been redrawn so the rate of time passage is 
still positive:


http://www.bbc.com/news/world-latin-america-28013157

I've seen one article that argues that this is more natural in the 
southern hemisphere, since the shadow on a sundial rotates CCW there.


- Dave
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Re: [time-nuts] Correcting jitter on the 1 PPS signalfrom a GPS receiver.

[Dave Martindale]

Is there any reason (other than cost) not to both series-terminate the 
source and parallel-terminate the sink?


When I was dealing with analog video, the standard distribution method was :

1. Buffer amplifier with high input impedance, very low output 
impedance, and a gain of 2 (so 1 V P-P input becomes 2 V P-P out)


2. A series 75 ohm resistor from the amp output to each individual video 
output.  This formed a 2:1 voltage divider with the 75 ohm coax to give 
1 V P-P on the cable.  It also isolates the loads from each other.


3. A single video signal could be looped through multiple high impedance 
loads.


4. 75 ohm parallel termination at the far end of the signal path 
(usually on the last device).


This way, every device along the way saw an undistorted copy of the 
signal.  The buffer amplifier sees a simple resistive load.  And any 
reflections are absorbed at both ends of the cable.


- Dave

On 15/09/2014 02:04, Fuqua, Bill L wrote:

A lot of devices have a low output impedance so that the signal can be split 
using a TEE adapter with little loss or need for a distribution amplifier.
However, the cables must be impedance matched at far end, scope input, to 
prevent reflections which are the source of the ringing.
You can match the impedance at the source and you will get a reflection which 
will then be absorbed by the source resistance. One way to do this
is to get a small 15 turn pot about 100 Ohms put it, in series with the input 
source and adjust it until the ringing is gone or you can put it at the far end
,input of the scope, to ground and do the same.  But the best solution is to 
get a good feed thru 50 Ohm terminator and put it on the input of the scope.
Bill




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Re: [time-nuts] Correcting jitter on the 1 PPS signalfrom a GPS receiver.

[Dave Martindale]

I will agree that the end termination is optional if you are delivering a
pulse signal to just one input, which is at the far end of the coax.

However, I think there's still a problem with series-only termination when
the pulse signal is daisy-chained through multiple inputs.  When you apply
5 volts through a 50 ohm terminator to a 50 ohm cable, the instantaneous
voltage on the coax is only 2.5 V.  A pulse of amplitude 2.5 V travels down
the cable, and reflects from the open far end.  The reflection travels back
along the cable to the source, raising the voltage from 2.5 to 5 V as it
passes.

A device input located at the far end of the cable sees a single edge of 5
V amplitude, so it's happy.  But anything located somewhere along the cable
run sees two edges: one from 0 to 2.5 V, then a constant 2.5 V for a period
equal to twice the delay of the remaining cable, then another edge from 2.5
to 5 V.  Depending on the input threshold, this in-between device might
trigger reliably on the first edge, the second edge, or not reliably on
either.

Having proper far-end termination is critical for analog video, where
daisy-chaining is common, and a reflection that's even 1% of the amplitude
of the original signal is likely to be visible as a ghost image.  With
pulse signals, maybe it makes more sense to use one cable per device input,
input plus lots of distribution amplifiers and splitters.

- Dave

On Mon, Sep 15, 2014 at 1:13 PM, S. Jackson via time-nuts 
time-nuts@febo.com wrote:

 Hi Dave,

 yes there is a reason.

 The standard 1PPS signal termination (Thunderbolt etc) used to be 5 Ohms
 or less series termination into a 50 Ohms coax (yikes), then end-terminate
 to  get rid of all the undesired reflections.

 Your example below is properly terminating a 75 Ohms coax with a 75 Ohms
 series termination. The end-termination then becomes optional and affects
 the
  signal level at the sink. So if a higher signal level is desired, simply
 leave  off the 75 Ohms end termination.

 But in the case of the Thunderbolt they don't use a 50 Ohms output
 impedance, they use something around 5 Ohms. That is the problem here: the
 total
 impedance mismatch from the very low source impedance into the 50 Ohms
 coax.

 The reason they do that is so that they can generate a proper signal
 level that is approaching 5V across the 50 Ohms end termination so that the
 signal remains CMOS compatible. Otherwise if they properly terminated the
 driver  with 50 Ohms they would have a voltage divider and would only
 generate
 2.5V  at the sink.

 bye,
 Said


 In a message dated 9/15/2014 06:04:34 Pacific Daylight Time,
 dave.martind...@gmail.com writes:

 Is there  any reason (other than cost) not to both series-terminate the
 source and  parallel-terminate the sink?

 When I was dealing with analog video, the  standard distribution method was
 :

 1. Buffer amplifier with high input  impedance, very low output
 impedance, and a gain of 2 (so 1 V P-P input  becomes 2 V P-P out)

 2. A series 75 ohm resistor from the amp output to  each individual video
 output.  This formed a 2:1 voltage divider with  the 75 ohm coax to give
 1 V P-P on the cable.  It also isolates the  loads from each other.

 3. A single video signal could be looped through  multiple high impedance
 loads.

 4. 75 ohm parallel termination at  the far end of the signal path
 (usually on the last device).

 This  way, every device along the way saw an undistorted copy of the
 signal.  The buffer amplifier sees a simple resistive load.  And  any
 reflections are absorbed at both ends of the cable.

 -  Dave

 On 15/09/2014 02:04, Fuqua, Bill L wrote:
  A lot of devices  have a low output impedance so that the signal can be
 split using a TEE  adapter with little loss or need for a distribution
 amplifier.
   However, the cables must be impedance matched at far end, scope input,
 to  prevent reflections which are the source of the ringing.
  You can match  the impedance at the source and you will get a reflection
 which will then be  absorbed by the source resistance. One way to do this
  is to get a  small 15 turn pot about 100 Ohms put it, in series with the
 input source and  adjust it until the ringing is gone or you can put it at
 the far end
   ,input of the scope, to ground and do the same.  But the best solution
 is  to get a good feed thru 50 Ohm terminator and put it on the input of
 the
 scope.
   Bill
 
 

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Re: [time-nuts] LTE-Lite Eval Kit available

[Dave Martindale]

Hello.  Please add me to the list of people interested in the LTE-Lite eval
kits.

(I did not send a previous email, and you did not lose it - I've just been
slow in writing).

Thanks,
Dave

On Tue, Sep 23, 2014 at 8:05 PM, S. Jackson via time-nuts 
time-nuts@febo.com wrote:

 Hello Time-Nuts,

 we put together an email list with the large number of email  info-requests
 I got for the LTE-Lite eval kits over the weekend.

 I have just sent an email to everyone on that email list from my  corporate
 email account.

 Unfortunately my AOL account has a tendency to eat emails, so if you did
 not receive the info email from me today and should be on that list then
 please drop me a line directly and I will add you to the list immediately.

 I apologize in advance in case I did not properly  capture your email,
 thanks,
 Said
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

[Dave Martindale]

Did you use one-ply, two-ply, or three-ply TP?

More seriously, your LTE-Lite differs in a couple of respects from the
batch of production ones, or at least my example.  Your TCXO seems to be
in a metal package (shiny gold colour) and open to the air, if I'm
interpreting the photo on your LTE-Lite page correctly (and also the photo
that Said posted in his divide-by-two document).  The production units have
the TCXO in a solid black package, probably black epoxy, with a blob of RTV
rubber on top.  So the production units are probably already somewhat
better shielded against drafts.

(Thanks for doing the tests, particularly for those of us who can't do
these tests ourselves.  I can only watch the 1 PPS of the LTE-Lite wander
with respect to the 1 PPS from my old Thunderbolt (Piezo oscillator), and
look at the worst-case variation, but I have no way of knowing how much of
the drift is due to each GPSDO).

- Dave

On Sun, Nov 23, 2014 at 11:24 AM, Tom Van Baak t...@leapsecond.com wrote:

 The short-term performance is 10x worse if you don't shield the TCXO from
 air, even if the ambient air is still. I suggested Said sell the product
 with some sort of engineered shield in place. Instead each of us will solve
 the problem in our own way; which is ok for a dev kit.

 For plots and photos showing performance with, and without, and with
 insulation see:
 http://leapsecond.com/pages/LTE-Lite/
 The difference is dramatic, especially if you are used to working with
 OCXO where this sort of effect does not occur.

 The insulation may be found in convenient rolls at many local stores. I
 used TP, which for this application is an acronym for Thermal Paper.

 /tvb
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Re: [time-nuts] Practical considerations making a lab standard with an LTE lite

[Dave Martindale]

The 20 MHz output should be OK, since it is series-terminated with 50 ohms
at the source and the buffer can source enough current.  The driver sees a
100 ohm load (50 ohm resistor in series with 50 ohm coax impedance) for
that 32 ns round trip time, so it will increase power dissipation (as you
note).  But the load at the far end of the coax should see a clean edge,
and the reflection should be absorbed when it returns to the source (due to
the source terminator).  Just don't look at the signal half way along the
coax.

The other outputs apparently don't have either the current drive or the
source terminator, so a long piece of coax is likely to do unpleasant
things to the edge.

In either case, if you want to run any of the signals 10 feet it's likely
better to run a very short connection from the LTE-Lite to a proper 50 ohm
line driver.  That gets the power dissipation off the board, and then you
can use drivers that give you whatever output swing you want, and which can
drive a 100 ohm load continuously so you can use parallel termination at
the far end.

- Dave

On Tue, Nov 25, 2014 at 12:23 AM, Hal Murray hmur...@megapathdsl.net
wrote:


 Said Jackson said:
  Correct, and thats why its all a bad trade off if you have to use 50 Ohms
  termination. Either more heat or more PN, and more circuitry.

  So driving 50 Ohms inputs is not optimal here, 1M inputs are much better
 for
  this purpose.

 That only works if you have a (very) short connection to the next stage.

 Things get interesting if you have, say, 10 feet of unterminated coax.

 10 MHz is 100 ns, or 50 ns between transitions.  Coax is ballpark of 5/8 c
 so
 that's 16 ns one way or 32 ns round drip.  That's 60% of the heat as well
 as
 lots of nasty reflections.

 (Somebody please check my numbers.)


 --
 These are my opinions.  I hate spam.



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Re: [time-nuts] LTR-Lite GPS

[Dave Martindale]

I assume the Venus chipset NMEA output sentence set is a subset of the 
uBlox NMEA output set, and the NMEA messages are sufficiently 
standardized that the uCenter software can read them and display the 
results in a meaningful way.  Any other program that reads and displays 
NMEA data (and can be set to 38400 bps, instead of NMEA default 4800 
bps) would likely work.


Of course, none of the commands in uCenter that configure the receiver 
are going to work, both because the receiver isn't a uBlox and because 
the serial port is unidirectional.  You only get status.


- Dave

On 25/11/2014 16:07, Joseph Gray wrote:

Looking closely at the board, I see it uses a Venus GPS chipset. And yet
folks here are using the ublox ucenter software with it. What am I missing?

Joe Gray
W5JG
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Re: [time-nuts] typical phase nosie and ADEV plot of an OCXO

[Dave Martindale]

Programs that try to turn text into a link will get the URL wrong due
to a missing space.  Fixed link:
http://gpstime.com/files/tow-time2011.pdf

On Wed, Mar 14, 2012 at 09:05, Azelio Boriani azelio.bori...@screen.it wrote:
 And don't forget the usual PDF
 http://gpstime.com/files/tow-time2011.pdfwhere you can find the
 comparison of typical Allan Deviations from various
 clocks on page 7.

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Re: [time-nuts] Why are 1PPS signals so skinny?

[Dave Martindale]

It is worth noting that skipping the end termination is probably a bad idea
when daisy-chaining a signal from one output to more than one device input.
 The input at the end of the cable will see a clean rise from zero to 5 V
(or whatever the driver's open-circuit voltage is), but the other inputs
along the length of the cable will not.  They will see an initial rise from
0 to 2.5 V as the series termination at the driver and the cable impedance
act as a voltage divider while the cable is being charged. Later, they will
see another step change from 2.5 V to 5 V as the reflection returns from
the open-circuit far end of the cable.  If the input threshold is
automatically set at half the input voltage swing, the input could trigger
on the outbound or the reflected pulse, or even somewhere in between.

This is in contrast to having a 50 ohm termination at the end of the cable
(plus the 50 ohm series termination at the source), where all inputs along
the length of the cable see a single edge transition from 0 to 2.5 V.  They
will each see the edge at a different time due to propagation delay, but
all will see a clean edge.

 Dave

On Tue, May 15, 2012 at 4:00 PM, saidj...@aol.com wrote:


 To make this work without the unnecessary power consumption simply remove
 the end-termination resistor, and use it as the series termination resistor
 (R1  in your schematic)! Done.

 Attached are two plots of a series terminated (~55 Ohms) high-speed  1PPS
 transmission from our CSAC GPSDO board zoomed-in  and zoomed-out to show
 the
 actual rise-time, and a longer time frame  view.


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Re: [time-nuts] Why are 1PPS signals so skinny?

[Dave Martindale]

For what it's worth, that seems to be the standard way to distribute analog
video (composite or component).  A low-impedance voltage source with a gain
of 2 drives a bunch of outputs with an individual 75 ohm series resistor
for each output.  Each cable that is connected to an output has a parallel
75 ohm terminator at the far end.  Inputs are all high impedance.  The
result is cables properly terminated at both ends (no reflections), unity
gain overall (the driver gain of 2 compensates for the 2:1 voltage divider
due to the terminators, and the ability to daisy-chain through several
inputs.

- Dave

On Tue, May 15, 2012 at 6:02 PM, Hal Murray hmur...@megapathdsl.net wrote:


 It's not uncommon to use both source/series and end/parallel terminations.
  The series terminator drops the signal level by 2 but minimizes
 reflections if you are working in a less than ideal setup.  It also
 provides a current limit on the driver in case something gets shorted.


 --
 These are my opinions.  I hate spam.




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Re: [time-nuts] Why are 1PPS signals so skinny?

[Dave Martindale]

But if the LED transition was offset any significant amount of time from
the PPS, you wouldn't be able to use it to set your watch!

Dave :-)

On Wed, May 16, 2012 at 10:57 AM, Magnus Danielson 
mag...@rubidium.dyndns.org wrote:


 Then, to reduce the impact on the PPS signals, the LED on/off could be
 forced to be phase-shifted to the PPS.



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Re: [time-nuts] Antenna question about RHCP/LHCP I'm sure a time-nut can answer

[Dave Martindale]

I don't think that's correct.  A right-hand spiral (however you define
right-hand) remains right-handed if you rotate the whole object in space so
the centre axis of the spiral points in the opposite direction.  A
right-handed spiral is converted to a left-handed one only by reflecting it
in a mirror.

Try this: pick up two identical bolts.  Think of the bolt heads as the feed
end of the antenna, with the threads being the helical element.  Rotate the
two bolts so they are aligned on the same axis, but facing each other.
 Note that the threaded portions of both bolts spiral the same way.  So two
identical antennas will work fine as a transmit/receive pair over an
open-space path.

But if you bounce a RHCP signal off some passive reflector, the signal
becomes LHCP (or vise versa), and the transmit and receive antennas need to
be mirror images of each other.

 Dave

On Mon, Jun 4, 2012 at 7:26 PM, Magnus Danielson mag...@rubidium.dyndns.org
 wrote:

 On 05/06/12 00:30, Dr. David Kirkby wrote:

 This is not exactly a time related question, but I'm sure the subject
 must be of interest to time-nuts using GPS.

 If one transmits from an antenna such as a helical one, RHCP, can the
 same antenna be used for reception, or does the helix need to be wound
 the other way?

 If you google this topic, there seems to be a lot of confusion about
 whether the TX antenna and RX antenna need to both have RHCP or whether
 one needs to be LHCP and the other RHCP.

 Given GPS uses circular polarization, I'm hoping someone here will know.

 It would appear there are different definitions of circular
 polarization, with one considering it from the point of view of the
 source, and the other considering it from the point of view of the
 receiver. The IEEE apparently uses the former, and others (especially
 optics) use the opposite.

 http://en.wikipedia.org/wiki/**Circular_polarizationhttp://en.wikipedia.org/wiki/Circular_polarization

 My aim was to make a gain measurement of two circular polarized
 antennas. I have two identical antennas, but are unsure if the signals
 should be received strongly, or whether theoretically no signal would be
 received. (Of course in practice, one never achieves perfect
 polarization, so there will always be a signal detected, even if
 cross-polarized.


 They would have to have opposite rotation.

 The waveform rotation will follow the transmitter antenna into the
 receiver antenna. The receiver antenna follows the same rotation that the
 transmitter antenna has, it's just that the face each other, so when you
 turn one of the 180 degrees such that they face the same direction you
 would see that they are in fact rotated in opposite directions.

 I'm sure the sat folks can confirm this.

 Cheers,
 Magnus


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Re: [time-nuts] Antenna question about RHCP/LHCP I'm sure a time-nutcan answer

[Dave Martindale]

Well, they could be consistent.

Most of those photos show only two sizes of helix-type antennas.  The
larger diameter (probably lower frequency) are quadrifilar helix designs,
and they are uniformly left hand thread helixes.  (I assume that everyone
agrees on what a left-hand thread looks like, no matter how they label
circular polarization).  The more numerous smaller diameter antennas are
multi-turn one-element helixes, and they always seem to be right hand
thread in all of the photos.  The smaller antennas are almost certainly
for L1.

The complication is the Block-IIR-M-SV-2S photo.  But it has *three*
sizes of antennas visible.  The largest are left-hand-thread quadhelix as
before, and thus likely close to the same physical dimensions as the large
antennas in the other photos.  The mid-size ones are multi-element
multi-turn helixes that look a lot like the quadhelixes in design except
that the ends are left open.  And they are about 2/3 the diameter of the
quadhelixes, much larger than the simple helix antennas in the previous
group, so probably for a different frequency.  Then there are the smallest
antennas, which appear to be a single-element helix with many many turns -
but these are about 1/3 the diameter of the large quadhelixes, and thus
*these* are likely the L1 antennas.  And, if I look closely, these small
helixes do appear to be right-hand-thread wound.

 Dave

On Mon, Jun 4, 2012 at 8:24 PM, Tom Van Baak t...@leapsecond.com wrote:

 David,

 One of these two photos is correct (odd isn't it)...
 http://www.ausairpower.net/Block-IIR-M-SV-1S.jpg
 http://www.ausairpower.net/Block-IIR-M-SV-2S.jpg

 Maybe these break the tie:
 http://www.spacemankind.com/images/ms/20090817-lockheed-gps-iir-lr.jpg
 https://share.sandia.gov/news/resources/releases/2008/images/GPS1.jpg

 http://www.lockheedmartin.com/content/dam/lockheed/data/space/photo/pressrelease/GPS_4A_pr.jpg
 http://www.insidegnss.com/auto/popupimage/GPSIIF_photo_lo.jpg
 http://www.freepatentsonline.com/6653987-0-large.jpg

 /tvb
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Re: [time-nuts] So, how did you spend your leapsecond?

[Dave Martindale]

I was invited to dinner with friends, so I took some stuff with me.  Before
dinner, I explained the concept of leap second to the hosts' 8-year old
daughter.  She understood leap years already, and I think she understood
the leap second explanation too.

As the appointed time (8 PM here, in EDT land):

- An Apple iPhone running Emerald Time displayed 19:59:60 flawlessly.

- I tried to use a web browser on an iPad to display www.time.gov.  That
was a dismal failure, probably because the time.gov web page uses Flash for
its counting clock, and Apple doesn't support Flash.  So the page was
there, but there was no clock.

- But my host had his PC laptop out, he was displaying www.time.gov too,
and it did show 19:59:60.  So we got to see it there.

- My Casio WaveCeptor watch, which had synced successfully with Fort
Collins at midnight this morning, did nothing.  So it's now running 1
second fast.  It will probably reset itself overnight, but that means it's
displaying the wrong time for 4 hours or more.  Tsk tsk.

However, I didn't bring a video camera, so I have no images of any of this.
 My hosts had never seen a leap second before, and they thought it was neat.

 Dave

PS: I looked up leap second on Wikipedia one hour after the event, and
someone had already updated the photo to show the most recent leap second
from the NIST page (not that it's likely to be much different from the
previous time).
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Re: [time-nuts] Modern motherboard with RS232 port

[Dave Martindale]

I like to think of it this way:
If you are talking instantaneous measurements, then watts is indeed always
volts * amps.  With a resistive load, the signs of volts and amps are
always the same, and the product of the two is always non-negative.  If you
calculate the average of instantaneous watts over time, you get average
power.

If you have an inductive load, watts is still volts * amps.  But the phase
shift between current and voltage means that the instantaneous power is
sometimes negative, which means that the load is (at that instant)
returning power to the source.  But averaging instantaneous watts, both
positive and negative values, still gives you average power.

The problem comes when we want to calculate watts with devices that only
measure voltage, or only measure current.  With a resistive load, where the
instantaneous power is never negative, you can calculate power by measuring
only voltage, calculating the RMS voltage, and knowing the resistance.  But
that doesn't work for non-resistive loads because the instantaneous current
is no longer proportional to the instantaneous voltage.  If both are still
sinusoidal, knowing the phase shift lets you calculate power.  But that
doesn't work either for arbitrary waveforms.

 Dave

On Sun, Aug 19, 2012 at 10:32 PM, Chuck Harris cfhar...@erols.com wrote:

 The long and the short of it is that when AC encounters a reactive
 load, it results in a current that is not in phase with the voltage.
 Power is equal to volts x amps only when the current and voltage are
 in phase which can only happen if the load is purely resistive.

 If you hang a perfect capacitor across the power line, or a perfect
 inductor, you will draw lots of current, but no power.

 -Chuck Harris


 Tom Knox wrote:


 Hi Ed;
 I may not have had enough coffee yet, but if Volt X Amps = Watts why
 would there be a difference?
 Best Wishes;
 Thomas Knox


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Re: [time-nuts] [OT] Ikea Lamp

[Dave Martindale]

If you care about accurate colour rendering, stick with incandescent, 
preferably halogen.  White LEDs are actually blue LEDs coated with a 
phosphor that absorbs some of the blue light and emits approximately 
yellow instead.  If you look at the spectrum, you'll see a broad yellow 
peak and a narrower blue peak.  Your eyes see it as approximately white, 
but it's deficient in red and green compared to a black body emitter 
like hot tungsten.  On the other hand, it's not as spiky as the output 
of fluorescents.


The particular IKEA units I have both look approximately daylight in 
colour temperature, and the colour is pretty uniform across the 
illuminated field (except for the very edge, which is yellow, but that's 
probably due to chromatic aberration in the lens, not the LED source).  
They work better than most of the LED flashlights I've seen, which tend 
to have large intensity and colour changes between the centre and the 
edge of the illuminated field.


Dave

On 30/01/2010 07:49, paul swed wrote:

IKEA and $39 per lamp. Sounds like some pretty good margin in the sale.
I guess these LED things will be main stream and save the world when we see
them at walmart for $6.

On my bench I converted to 60 watt halogen lamps compared to the 100 watt
lamp.
Equivalent color spectrum to the traditional lamp also. For as many hours as
that light is on. I suspect I am saving some money in the long run.

Curious are these lights truly white or do they tend towards a traditional
lamp spectrum.
Regards

   



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Re: [time-nuts] White LED's

[Dave Martindale]

Hmm.  Has anyone built a strobe light using LEDs instead of a xenon 
flash tube?  I can see the appeal of building something that doesn't 
need high voltage to fire or trigger the tube.  Yes, you probably 
couldn't get as much light as a big Xenon tube, but there are 
applications where you don't need to illuminate a large area.  (Recent 
example of where I wished I had a stroboscope: looking at the balance 
wheel of a pocket watch).


How high can you push the drive current of a LED if the pulse is short?  
Of course you have to keep the average dissipation below what the device 
is rated for, but there must be a peak current limit too.


Dave

On 30/01/2010 01:17, Robert Atkinson wrote:
Hi,I'm late to the thread (as usual), but have looked at these LED's in the past. It was for a biotech imaging application. There are two types, a red/green/blue cluster or a blue / near UV LED with a white phosphor. These phosphors seem to have a fairly continuous spectrum, at least compared to fluorescent lamps and HID lamps. What surprised me was the speed. We had a strobe application for which a xenon strobe was proposed. I tried LED's (our optics expert said even normal LED's would not be fast enough). I knew normal LED's are fast enough but was unsure about the phosphor types. To my surprise they where faster than the xenon tube! They were faster than my detector. This has has an impact on the mill illumination in that you can get strobe effects that could cause you to think the spindle was stationary when it was not. This is more of a problem in a noisy environment than a home shop with only one machine running.  
Robert G8RPI.


   




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Re: [time-nuts] Conducting Bench Top Material

[Dave Martindale]

There are also large differences in rated lifetime; look at the fine 
print on the package.


I've had some early Philips units that I used in a timer-driven lamp; 
they were on for hours every day.  The lamp lasted for years and years 
and I eventually threw it out because it had gotten dim (the tube was 
visibly blackened inside), but it was still working.  It was rated for 
1 hours, and probably reached that before I junked it.


On the other hand, I've had some cheap Ikea lamps fail in ceiling lights 
in little more than a year.  The electronics self-destructed.  Took a 
close look at the package for a new one, and they are rated for only 
2000 hours - which is easy to use up in a year in a room where the 
lights are on 6 hours every evening.


Now, using CFLs of any type reduces electricity use compared to 
incandescent, and that's worthwhile in many applications.  But CFLs also 
add a bunch of electronics parts to the waste stream when they are 
thrown out - they're much worse than incandescents in that respect.  So 
when I use fluorescents, I prefer replaceable-tube units (where the 
electronics in the ballast will last for decades, not be replaced every 
couple of years).  In places where I need a screw-in self-ballast type, 
I look for the more expensive 10,000 hour types instead of the cheap 
2000-hour ones.


And, as someone else pointed out, it doesn't make much sense to use CFLs 
in applications where they are turned on and off a lot, since their life 
will be much shorter than rated.  (But LEDs should be fine for this, 
once the price comes down a bunch).


Dave

On 30/01/2010 05:31, Didier Juges wrote:

Also they are very sensitive to heat, so do not use them in an enclosed
fixture.

I have been burned (figuratively) with these two gotchas, there may be more.
The one that lasts the longest in my house is the outside light at my back
door. It is turned on once a day around 6-7 PM and off in the morning, so
about 12 hours a day every day, and it lasts for years at that rate. Those
in the bathroom that get to be turned on and off several times a day for a
relatively short time don't do nearly as well.

Didier
   



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Re: [time-nuts] GPS Antenna

[Dave Martindale]

In theory at least, a single satellite is enough to provide timing in
position hold mode.

However, that assumes you get a direct line-of-sight signal, with no
multipath.  A reflected signal has additional delay that the GPS
receiver cannot factor out if it's receiving only one satellite.  If
it is receiving many, it *might* be able to tell which ones have
multipath delays and ignore them.

A high antenna tends to have good line-of-sight reception of the
satellites, as well as receiving more of them.  The former might be
more important than the latter.

 Dave

2011/9/12 Miguel Gonçalves m...@miguelgoncalves.com:
 Hi Chris!

 Here and on ntp-questions always helping me out! Thanks!

 Moving it up to the roof would be difficult. Would have to talk to all
 neighbours to ask permission to run a cable to the roof. I'll have to keep
 it at this location.

 Anyway, in position hold I would assume that using 2 satellites will give me
 good time. Right?

 Thanks again!

 Cheers,
 Miguel

 On 12 September 2011 16:03, Chris Albertson albertson.ch...@gmail.comwrote:

 2011/9/12 Miguel Gonçalves m...@miguelgoncalves.com:..
  oncore# /var/tmp/sats.sh
  8 satellites:        0
  7 satellites:        0
  6 satellites:      870
  5 satellites:     7941
  4 satellites:     7313
  3 satellites:     6385
  2 satellites:      575
  1 satellites:        0
 
  The machine has been running for 6 hours and it has been seeing a good
  number of satellites for most of the time.
 
  Do you think I should buy an external antenna .


 It looks like your current antenna can only see about 1/2 of the sky.
  The reason to replace it is so you can see the entire sky.  the
 Panasonic would be ideal because it has enough gain to drive a long
 cable.   THere  is no resin to replace the antenna unless you intend
 to  place it in a better location.   A higher gain at the same
 location will not give you a better view of the sky.

 Any outdoor antenna needs to be pointed or have a dome shape so that
 whatever falls on it rolls off.
 --

 Chris Albertson
 Redondo Beach, California

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Re: [time-nuts] Monitoring the Rapco 1804M - how antenna changes affect the unit

[Dave Martindale]

By the way, this doesn't mean that the GA-27 is a poor antenna design,
it's just not the best antenna choice for this situation.

The GA-27 is intended as an external antenna for Garmin's handheld
receivers, which normally operate with passive patch or helix
antennas.  So the receiver itself needs to be sensitive enough to work
well when an unamplified antenna is connected directly to the
receiver, and the GA-27 preamp only needs to provide enough gain to
overcome the losses in the cable plus a bit more.  Additional gain
could be detrimental in some circumstances (e.g. when placed near
transmitting antennas on a vehicle), so the GA-27 might well be the
best antenna for the Garmin handheld receivers.

But a GPS board module is intended to be built into some piece of
equipment, and probably expected to always be fed from a remote
amplified antenna, never a local passive antenna.  In those
circumstances, it makes sense to put all the necessary gain at the
antenna preamp and let the receiver be less sensitive.  The
manufacturer will recommend some antenna for use with the receiver,
and though you don't usually have to use that particular antenna, it's
probably a good idea for your antenna/cable/splitter setup to provide
roughly the same signal level at the receiver.

- Dave

On Wed, Nov 2, 2011 at 01:19, David J Taylor
david-tay...@blueyonder.co.uk wrote:
 I've made a small Web page describing what happened when I changed the
 puck antenna on a Rapco 1804M for a more sensitive one.  The Rapco 1804M
 expects a big outside antenna.

  http://www.satsignal.eu/ntp/Rapco-1804M-notes.html

 This page has now been updated to provide a comparison between three puck
 antennas - the Garmin GA 27 (BNC), a 3rd-party low-cost puck, and a Gilsson
 puck antenna.  It seems that the even higher signal level from the Gilsson
 benefits the 1804M more than the other two.

 Cheers,
 David
 --

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Re: [time-nuts] gravity controlled pendulumn clock?

[Dave Martindale]

On Tue, Dec 13, 2011 at 08:19, Chuck Harris cfhar...@erols.com wrote:

 Metric vs English is purely about a set of arbitrary constants.

 Decimal pounds, decimal inches and decimal seconds is just as
 arbitrary, and just as easy to use as the metric system.

I would agree, as long as you stay within a single version of the
English system.

But where the metric system has an advantage is that the units with
the same name are the same size everywhere; that's not true of
English units.  I can remember mixing Kodak photographic chemicals
for darkroom use, where the mixing instructions are in terms of ounces
and gallons.  But I was in Canada, where the Imperial (British) ounce
and gallon are both different volumes than the American (and thus
Kodak) units of the same name.  I didn't *have* measuring cups with US
ounce markings.  We solved the problem by converting the foreign
units to ml and litres, which we were equipped to measure.

If I remember correctly, Ilford's photo chemical mixing directions
were already in metric, so they applied worldwide without any units
confusion.

Fortunately, the inch seems to be the same size everywhere, so I don't
have to figure out whether someone is talking about British inches or
American inches.  I have a small lathe with inch leadscrews, and a
small milling machine with metric leadscrews.  Neither measurement
system is particularly better or worse than the other.  Many of my
measuring tools can display in either system.

Imagine the chaos if the second was a different length of time in
different countries.

- Dave

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Re: [time-nuts] 32768 Hz from 10 MHz

[Dave Martindale]

On Thu, Feb 2, 2012 at 12:21, Tom Van Baak t...@leapsecond.com wrote:

 It's possible to use Bresenham with two integers 10,000,000 and
 32,768 but I found no way to perform all the 24-bit calculations
 on an 8-bit PIC quick enough. Removing the GCD often helps
 but in this case the accumulator remains 3-bytes wide.

In this particular case, the divisor your want is 2^15 / 10^7.  You
can remove a common factor of 2^7, giving 2^8 / 5^7, or 256 / 78125.

If you only want a square wave output, you should be able to do this
with a 17-bit binary counter and some logic.  In concept, it looks
something like:
- initialize register to 0
- every input clock, add 256 to the register
- when the register is greater than or equal to 78125, set overflow
bit and subtract 78125 from the register.

In practice, you'd probably set the register to 78125 and count down
to zero, using the borrow output from the subtract of 256 as
overflow.  Then you don't need to compare the register to 78125.

Essentially, you've built a special-purpose DDS whose frequency
resolution is 128 Hz , and the output frequency you want is exactly
256*128 Hz.  The average frequency is exact, and the output waveform
repeats every 1/128 sec.

 I'm curious how a 10 MHz-driven high-end DDS would generate
 32 kHz with the lowest possible jitter?

You should be able to use a AD9913 to do the same 256/78125 division
described above, with exact output frequency, and sine wave output to
boot.  If I've understood the datasheet correctly, you would program
the main DDS frequency tuning word to 14073748, which gets you as
close to 32768 Hz as possible without exceeding it.  Using variable
modulus mode, you program the FTW and modulus of the secondary DDS to
65276 and 78125.

Every input clock, the main FTW of 14073748 is added to the main
32-bit register.  At the same time, 65276 is added to the secondary
register.  If the secondary register exceeds 78125 (which will happen
on most clocks with these values), the main register is incremented by
1 and the secondary register has 78125 subtracted.  So over the course
of 78125 input clocks (1/128 second), the secondary register has
65276*78125 counts total added, which causes it to overflow 65276
times.  The main register has 78125*14073748 added to it directly,
plus 65276 extra counts from the secondary register overflows.  The
sum of those two values is exactly 2^40, meaning the main register
overflows 2^8 times in 78125 clocks.

After 78125 input clocks, both the main and secondary register have
returned to zero, so the sequence repeats exactly every 1/128 second.
In effect, the secondary register is acting as a variable-modulus DDS
that changes the FTW of the primary fixed-modulus DDS by only one
count, just often enough to make the division ratio exact.  And
because the primary DDS is still fixed-modulus, you can still use the
top k bits of the accumulator to index into a sine lookup table, and
produce a sine wave output.

 Dave

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Re: [time-nuts] LTE Lite SkyTraq chip info

[Dave Martindale]

I spent a bit of time poking around the SkyTraq web site on the weekend.  I
couldn't find a datasheet for the chip on the LTE-Lite - perhaps it's so
new that SkyTraq has not put together the datasheet yet.

Under timing, they only list the Venus638LPx-T, which is a older (2011
copyright on the datasheet) 65-channel receiver.  The LTE-Lite
documentation mentions 65 channels somewhere too, suggesting that the
LTE-Lite started out using this chip.  Under navigation receivers, Skytraq
lists the newer (2013) Venus838FLPx with 167 channels.  So I would assume
that the Venus838LPx-T-L used in the LTE-Lite is the same 167-channel
hardware with timing firmware, and that the LTE-Lite switched from the
638LPx-T to the 838LPx-T-L sometime during development.

- Dave

On Tue, Nov 25, 2014 at 5:12 PM, S. Jackson via time-nuts 
time-nuts@febo.com wrote:

 Now that the cat is out of the bag - notice that on these boards we used
 the special -T timing version which is more than twice as expensive than
 the
 normal navigation version used by others.. I personally use the uBlox
 software because the Skytrack software had a habit of crashing itself and
 my
 computer from time to time..


 In a message dated 11/25/2014 14:02:41 Pacific Standard Time,
 paulsw...@gmail.com writes:

 Here is  a link to a company that at least shares details of the SkyTraq
 venus 8  chip on the LTE-Lite. The actual skytraq sites is pretty  useless.


 https://www.tindie.com/products/smokingresistor/venus838flpx-gps-breakout-bo
 ard/

 There  is a program that will read the nema codes and such also.
 Have used it and  its not better or worse then ublox. A bit of humor it
 only
 ever shows Asia  for the ground track.

 The venus 8 seems to have a lot of capability.  Not sure how to get to it,
 but the fact is for the LTE Lite its not needed.  It has a single job to
 perform.
 It would be curious to obtain the board  tindie sells because it supports
 all of the satellites. But have to say  thats a project for another day
 wa down the list.
 But at least you  can have some further technical details for the  system.
 Regards
 Paul
 WB8TSL
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Re: [time-nuts] 10MHz LTE-Lite - PPS accuracy?

[Dave Martindale]

What is the source of the 1 PPS you are comparing against?

I compared my LTE-Lite to an old Thunderbolt (original model, single 24 V
input with internal DC to DC converters, Piezo oscillator).  At the time,
the Thunderbolt had been running for a few months, while the LTE-Lite had
been running for a week or so.  Antennas were sitting on the window ledge
of a west-facing window, so relatively poor sky coverage.  I connected the
PPS outputs from the two GPSDOs to two channels of a digital scope and left
it running in accumulate mode.  A couple of the resulting displays are
attached below (I hope).  Yellow trace is the Thunderbolt PPS, also the
trigger source.  The LTE-Lite is the cyan trace.  Each image shows signals
accumulated over a period of about 8-12 hours.

As you can see, the relative timing of the two 1 Hz signals wanders by
about +- 100 ns around a midpoint value, but at this midpoint the LTE-Lite
is around 50 ns later that the Thunderbolt.  (I call it a midpoint
because it's judged by eye as halfway between the two recorded extremes.  I
don't have a record of the individual measurements, so I can't calculate
mean or median).  The Thunderbolt's antenna cable is perhaps 10 feet
shorter than the LTE-Lite's, so that accounts for ~15 ns (Thunderbolt
antennas compensation is set to zero).

So, at my house, the LTE-Lite is about 50 ns late (or the TB is 50 ns
early).  That's one cycle of the LTE-Lite 20 MHz TCXO - coincidence?

I also have an old Garmin GPS-25 board.  This is a navigation GPS, without
timing features, but it does have a 1 PPS output.  I've included one
capture of GPS-25 vs. Thunderbolt.  The jitter is much worse; most (but not
all) traces are within +- 400 ns of the Thunderbolt (note the different
horizontal sweep).  And there is also an overall bias: the Garmin receiver
appears to be about 100 ns late on average compared to the TB.

Unfortunately, I don't have any other way to measure which GPSDO has the
more accurate PPS, and which one is responsible for most of the jitter.  (A
man with two GPSDOs never knows what time it is, precisely).

I do have a big old 5 MHz OCXO pulled from a Transit receiver which is
probably quite stable, but it is 0.2 Hz off nominal frequency and is not
adjustable.  Viewed on a scope alongside either GPSDO output, the 5 MHz
phase shifts by one cycle every 5 seconds, too fast to make any comparison
by eye of the stability of either GPSDO.

- Dave

On Mon, Dec 8, 2014 at 7:17 AM, David J Taylor 
david-tay...@blueyonder.co.uk wrote:

 On the 10MHz LTE-Lite, how far out from true UTC would the PPS be expected
 to be?

 It seems to be about 200+ ns late on my unit, although it is much more
 stable than a typical GPS/PPS produces.

 Thanks,
 David
 --
 SatSignal Software - Quality software written to your requirements
 Web: http://www.satsignal.eu
 Email: david-tay...@blueyonder.co.uk
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Re: [time-nuts] PRS-45A is alive!

[Dave Martindale]

One zero-effort way to do this: a portable GFCI.

I have several GFCIs (Ground Fault Circuit Interrupters) designed for
portable use.  They may be in the form of an extension cord with the GFI
electronics in the male plug, or a short cord with the electronics in the
middle of the length, or a small block that plugs into an outlet, with a
female outlet that a device plugs into.  All of these portable GFCIs
require line power to remain in the on position.  If the AC is
interrupted briefly, the GFCI drops out and stays off until manually reset.

This must be by design, because it is different from the behaviour of GFCI
outlets, and GFCI circuit breakers.  It mimics the behaviour of latching
magnetic contactors (relays) used on large AC-powered tools.  I use the
portable GFCIs to get the same shut-off-and-stay-off feature for small shop
tools that are equipped only with an ordinary switch.  A portable GFCI
should work just as well for electronics that you want to stay off until
manually reset.

- Dave

On Tue, Dec 9, 2014 at 1:24 AM, wb6bnq wb6...@cox.net wrote:

 Hi Bob,

 I think using a latching relay is a very good idea and prudent.  Besides
 while it is reacquiring lock you would probably be busy resetting VCR's and
 so forth.

 BillWB6BNQ


 Bob Stewart wrote:

   Hi Pete,
 I don't have any way of knowing.  I've asked the seller if he has a copy
 of the control software, and I don't like to go back with a bunch of petty
 questions like that.  The next issue is adapting some serial port software
 i wrote to the protocol in the manual Magnus sent to see if I can pull the
 status codes out.  That would probably tell me something.
 I have some tests I want to run immediately on my GPSDO and the KS to
 settle the question of which one can't keep time.  After that, I'll power
 it down, lift its skirts and take some pics.  It's pretty simple on the
 surface: a Cs Beam Tube, a main board, a microwave package with MTI 5Mhz
 OCXO, and the HV and LV power supplies.
 I don't intend to keep this thing running 24/7, but I have a question:
  Here in Houston, we have the occasional large thunderstorm and resulting
 short power outages.  So, should I put a latching relay in the power stream
 to keep it off if I lose power?  The budget is now officially busted, and a
 UPS is not going to happen for awhile.  Santa's sleigh is now officially
 out of gas.
 Bob
  From: Pete Lancashire p...@petelancashire.com
 To: Bob Stewart b...@evoria.net; Discussion of precise time and
 frequency measurement time-nuts@febo.com Sent: Monday, December 8,
 2014 11:46 PM
 Subject: Re: [time-nuts] PRS-45A is alive!
   Love to have known how long it was off, and how much of that 16
 minutes was getting the tube degassed.

 -pete



 On Mon, Dec 8, 2014 at 7:11 PM, Bob Stewart b...@evoria.net wrote:


 Well, it's alive, and I even have 10MHz coming from it.  It took about
 16 minutes to go to lock.  Is that good, or doesn't matter?  Now I've got
 to put together a serial cable and see if I can talk to it and find out how
 it thinks it's doing.  But, this is good!


 www.evoria.net/AE6RV/PRS-45A/2014-12-08%2020.51.33.jpg

 Hope you enjoy the wall decorations.  =)

 Bob - AE6RV
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Re: [time-nuts] 10MHz LTE-Lite - PPS accuracy?

[Dave Martindale]

In my case, the LTE-Lite had been operating for at least a week before I
made my accumulate mode measurement, and the Thunderbolt had been
operating for at least a month.  But both antennas were in poor locations -
not bad enough to lose lock any time I was watching, but nowhere close to a
clear view of most of the sky.  I never saw the 1 PPS disappear while I was
watching it.

I wonder if your LTE-Lite ever finished its survey and switched into
1D/position hold mode?  A GPS operating in 3D mode can indeed fail to get a
position fix with 5 satellites being received, if they have bad geometry
(e.g. all are in the same plane in space) because the solution will have
horrible DOP values.  But a timing-mode GPS in position hold mode knows its
own (antenna) position, and only needs one visible satellite to continue to
provide timing outputs.

We don't know how the LTE-Lite's disciplining algorithm is tuned.  If
frequency stability was considered to be more important that timing, the
algorithm may limit the maximum frequency offset that can be used to
correct a timing error.  Watching the scope output in real time, I can see
the time offset between the two 1 PPS pulses change with time, but it
always changes rather slowly, so the maximum frequency difference I've seen
is quite small.  (I no longer have the equipment set up, so I can't provide
a quantitative number).

- Dave

On Tue, Dec 9, 2014 at 5:13 AM, David J Taylor 
david-tay...@blueyonder.co.uk wrote:

 I work with Said at Jackson Labs.  I've been reading the time-nuts
 discussion for a few years, but rarely chime in.  I saw this discussion and
 wanted to make a couple points.

 * The LTE Lite time accuracy specification corresponds with the Skytraq GPS
 receiver's specs page which I have attached.  The specification is for the
 output directly from the GPS receiver available on the LTE Lite Eval
 Board's JP1 connector pin 12.  This specification assumes optimal antenna
 placement and thermal conditions, and position hold mode. It is also an RMS
 (1-sigma) measurement not a peak-to-peak measurement.

 * The GPSDO-generated 1PPS on the LTE Lite Eval Board's J1 connector has a
 phase offset to the GPS raw 1PPS that is shown in the PJLTS message (2nd
 field).  The GPSDO functions to drive this phase offset to zero.  But at a
 given time--especially shortly after power up--the offset may 100 ns or
 more.

 Keith
 ==

 Keith,

 Thanks very much for chiming in, as it has resolved what we are seeing,
 particularly your second comment.

 One thing I do notice is that the device appears less sensitive than some
 other GPS devices I have.  Perhaps sensitive isn't the correct word, but
 looking at the NMEA output it seems to indicate bursts of no/invalid
 position a lot more often than I would expect.  This is shown by the all
 the signal strength bars being grey rather than some of them being blue.
 I've also seen times when five or more satellites are above strength 29,
 and yet there is no position shown.  This also seems to stop the generation
 of the PPS output, which would be not so good when driving an NTP server.

 I am wondering whether this is due to overly stringent criteria being set
 for a position found, at least for my location and antenna location, and
 if this is the case, whether there is any chance of relaxing those
 criteria. I'm guessing not, as the device will not accept any serial input.

 You will have gathered that my main interest is time rather than
 frequency, and it seems that other GPS devices give PPS outputs which are
 nearer to UTC but they have considerably more jitter.  I'm only seeing this
 on the 'scope - likely my PCs would bother with a microsecond either way.


 Cheers,
 David
 --
 SatSignal Software - Quality software written to your requirements
 Web: http://www.satsignal.eu
 Email: david-tay...@blueyonder.co.uk
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Re: [time-nuts] ADEV noise floor vs counter gate time

[Dave Martindale]

 in the manual is ...+ 2 counts
 and though this relates to the 50MHz clock, perhaps they use a similar
 algorithm for the input frequency.

 I completed the 0.3 second measurements and the curve is similar to 1
 second but higher up (i.e. as you'd expect by extrapolation from the
 behaviour of the other curves).

 My ADEV calculation is based on the average frequency in each bin, the
 varying size of the bin should be insignificant as long as it is not
 affecting the average value within the bin. If the average frequency shifts
 by delta_F in one bin time step and the first bin is delta_T short (as a
 fraction of one bin time step) then the first frequency will be
 delta_T*delta_F low and the second bin perhaps that much high but the key
 point is that it is the product of the two deltas so it won't materially
 affect the accuracy of the calculation. At least I think that is correct.

 Taking the worst possible case where the delta in bin size always went the
 wrong way so every term in the Alan Variance sum was multiplied by
 (1+2delta)^2 then the final Alan deviation might be (1 + 2 delta) too big
 but as delta is of the order of 10E-8 or less this wouldn't even register
 on the graphs.

 What I might try doing is programming your approach into the code to try
 and get at the raw data - I only need to try 88,90 and 92 as possible
 counts - though to be sure I'll try mean frequency +- 5 say and then try
 and get the 50MHz clock values out as integers. What I might also do is
 then do a least squares fit (linear regression) to get the frequency over
 each bin and use the slope (this perhaps is what the counter does
 internally - I don't know).

 I'd like to get to the bottom of this if only to understand my counter
 better.

 James







  -Original Message-
 From: Dave Martindale dave.martind...@gmail.com
 To: jpbridge jpbri...@aol.com; time-nuts time-nuts@febo.com
 Sent: Wed, 18 Mar 2015 1:26
 Subject: Re: [time-nuts] ADEV noise floor vs counter gate time

  I believe I see the pattern.  As you figured out, you wouldn't expect a
 single period to be a multiple of 20 ns; you expect the length of (about)
 90 periods to be an integer multiple of 50 ns, since that's what the
 counter actually measures.  Further, the measuring time isn't exactly 1
 second, it is an integer number of periods of the input frequency that
 makes up at least 1 second.  If the counting logic was all hardware, you
 would expect to capture either 90 or 91 cycles of the input, depending on
 whether the input frequency was slightly below or above 90 Hz respectively.

 I built this table of your frequency data in Excel.  Math is 64-bit
 floating point, equivalent to about 16 decimal digits, so plenty accurate
 enough to simulate this counter:

 ReadingInput Count TB Count  Rounded  Frequency   Interval
  90.6359925074.998507590.6359
 1.01500
  90.7591925068.002506890.7591
 1.01360
  89.9640905002.000500289.9640
 1.00040
  89.8740905007.000500789.8740
 1.00140
  90.6007925076.997507790.6007
 1.01540
  89.6040905022.000502289.6040
 1.00440
  90.8648925061.999506290.8648
 1.01240
  90.8472925062.999506390.8472
 1.01260
  90.00011465925046.001504690.00011465
 1.00920
  90.00014459925028.998502990.00014459
 1.00580

 The first column is your data.  The second column is a guess about how
 many input cycles were captured.  The third column is the number of
 timebase cycles that have elapsed since the previous reading, based on the
 first two columns.  I hand-tweaked the numbers in the second column until
 the number in the third column was within 0.003 of an integer.  The fact
 that I was always able to do this tells me that my guess is probably
 correct, and the small residual (which is a few parts in 1e-10) is due to
 the counter rounding the results to 10 digits.  The 4th column is the
 result of rounding the previous column to the nearest integer.  This is
 what I believe is the actual number of counts the counter saw.  The 5th
 column is a fresh calculation of frequency, based on the integer number of
 input cycles in column 2 and the integer number of timebase cycles in
 column 4.  When the result is rounded to 10 digits, you can see it matches
 the 10 digits that the counter provided back in column 1.

 Oddly, the counter never captured 91 input cycles.  If the input frequency
 was a little higher than 90 Hz, it always measured at 92 cycles, even
 though 91 cycles was well more than 1 s since the previous reading.  I
 guess the microprocessor running the counter only checks periodically (e.g.
 every 20 ms) to see if the gate time has elapsed, and then latches the
 counts on the next

Re: [time-nuts] ADEV noise floor vs counter gate time

[Dave Martindale]

 and calculating a 10-digit period for display, the result 
always matched what the counter output.  Again, I think we know with high 
probability just how many input and timebase cycles were counted for each 
measurement.


I adjusted column 2 by eye, while looking at the results of column 3, but that 
process could be automated pretty easily (just not in Excel).  As I tried 90, 
91, and 92 in sequence, there was always just one of those which gave a small 
residual error.


So I think your TF930 is making measurements and accurately converting them to 
frequency or period, with a +- 20 ns uncertainty for each measurement.  Since 
it is a time-stamping counter, the uncertainty in a 10 s or 100 s or 1000 s 
measurement time (assembled by external software) is still only 20 ns.  That's 
great, but to actually get that accuracy over a long measurement time, you 
will need to determine and add up the actual number of input counts and 
timebase counts.  And you will have to understand that the counter does not 
make measurements at constant or near-constant intervals (e.g. every 90 cycles 
of input, without exception).  It gives you measurements whenever it gets 
around to measuring them.


Too bad there doesn't seem to be a way to get it to return the raw observed 
data (input cycle count, timebase cycle count) instead of the frequency or 
period derived from them.  That would make it trivial to string together a 
bunch of 1s measurements into arbitrarily long gate times.


- Dave

On 17/03/2015 05:57, jpbri...@aol.com wrote:

Hi Dave,

Thank you for your detailed response.

I use the E? command because it returns results at the gate time intervals 
rather than at the LCD update rate (as you point out). I think that this is 
working correctly because I get very different file sizes.


The numbers are returned as strings of 10 digits - here are some for 1 
second gate:


90.6359e+0Hz
90.7591e+0Hz
89.9640e+0Hz
89.8740e+0Hz
90.6007e+0Hz
89.6040e+0Hz
90.8648e+0Hz
90.8472e+0Hz
90.00011465e+0Hz
90.00014459e+0Hz

I generally use the frequency mode but I also tried time period and found I 
got the same curve in essence, which was comforting in a way but showed it 
wasn't rounding in converting to frequency.


The numbers above, on my calculator at least don't exactly match counts of 
20 nanosecs.


Here are some time period results:

11.11107736e-3s
11.0130e-3s
11.0769e-3s
11.0435e-3s
11.0593e-3s
11.0022e-3s
11.4000e-3s
11.e-3s
11.0370e-3s

Again they don't seem to be integer values of 20 nanosec exactly, though 
quite close. For example

11.11107736E-3/20E-9 = 555,553.868
555,554 x 20E-9 = 11.11108E-3

But I guess what it returns is the ratio of counts within the gate. So 
11.11107736E-3 period will occur

90 times in a second (as it is slightly short) and so I should take the ratio:

90 x 11.11107736E-3/20e-9 = 49,999,848.12

so still not quite an integer but if I assume the count (of 50MHz periods) 
was 49,999,848 and calculate one 90 th of it I get:


49,999,848 x 20E-9/90 = 1.07733

Still not exact agreement. I note that .12 is very close to .125 or 1/8 but 
I don't know if that is significant.
It is probable that it rounds the ratio in binary and then converts to 
decimal to print out.


I've tried assuming 89 periods and 91 periods but still don't get exact 
integer ratios.


Anyway, as I get good agreement between period and frequency measurements at 
1 sec, I don't think that it is a rounding issue.


I do think it is a quantization issue down to the +/- 20 nanosecs/gate time 
but I can't quite work it out.


I'm currently doing a run at 0.3 secs gate time and I'll see what sort of 
curve that produces.


Tomorrow I should receive my new Tek counter (I went for the fca3100 in the 
end as I got a very good discount on an ex demo unit) and that should give 
something to compare (once I've worked out how to program it).


James


-Original Message-
From: Dave Martindale dave.martind...@gmail.com
To: jpbridge jpbri...@aol.com; Discussion of precise time and frequency 
measurement time-nuts@febo.com

Sent: Tue, 17 Mar 2015 0:27
Subject: Re: [time-nuts] ADEV noise floor vs counter gate time

How is the counter configured?  Are you reading period or frequency?  Are 
you in E? (Every Result) mode, or C? (Continuous Result) mode?  The 
former should give you continuous but independent measurements, while the 
latter gives heavily overlapped measurements.  (For example, with a 100 
second gate time, you get one E output every 100 seconds, which covers a 
different 100-second period than the previous measurement.  In C mode, you 
get one output every 2 seconds, each of which is an estimate from 100 
seconds of measurement, but 98 seconds of that data was also part of the 
previous output and only 2 seconds of new data is included).


What does the data returned by the counter actually look like?  The manual 
implies that you always get 10 digits

Re: [time-nuts] ADEV noise floor vs counter gate time

[Dave Martindale]

How is the counter configured?  Are you reading period or frequency?  Are
you in E? (Every Result) mode, or C? (Continuous Result) mode?  The
former should give you continuous but independent measurements, while the
latter gives heavily overlapped measurements.  (For example, with a 100
second gate time, you get one E output every 100 seconds, which covers a
different 100-second period than the previous measurement.  In C mode, you
get one output every 2 seconds, each of which is an estimate from 100
seconds of measurement, but 98 seconds of that data was also part of the
previous output and only 2 seconds of new data is included).

What does the data returned by the counter actually look like?  The manual
implies that you always get 10 digits worth of result (not including the
exponent) regardless of gate time, but are the values rounded for display
in 7, 8, or 9 digits at the shorter gate times, or are they a full 10
digits always?  Given any particular value of frequency or period you get,
you should be able to reverse-calculate the number of whole cycles of the
input signal that the counter used as a gate time, and the number of cycles
of 50 MHz timebase that were counted in that period.  Since the counter
doesn't have interpolators, both of these values should be integers, and so
the possible output values are a small subset of all possible 10-digit
values for the shorter gate times.

For example, if the difference frequency is exactly 90 Hz, the period
between two 1 second measurements will be exactly 1 second, and the
counter will record 90 cycles of input and 5e7 cycles of timebase,
exactly.  In frequency mode, the output should be 90.0 Hz exactly, and in
period mode the output should be 11. ms.  Now suppose that the
difference frequency is just a hair slow, enough that 90 cycles of input
spans 50,000,001 counts of the timebase.  The reported frequency should be
89.9820 Hz and the reported period should be 11.1133 ms.  With a 1
s gate time, no values between those are possible unless the values are
being rounded (or there is an error in the calculation, which is always
possible).  Looked at another way, the smallest possible change in the
reported period is one timebase clock (20 ns) divided by the number of
input cycles in one gate time (90 for 1 s).

If the counter is rounding, you may be able to unambiguously figure out
what the actual inputs (cycles of input and cycles of timebase) to the
calculation were, and use that instead of the rounded value in your
calculations.  Rounding may round up or down, but if the two oscillators
are stable enough the direction can be predominantly up or down for
long periods of time, adding a bias to the actual frequency or period
you're measuring.  (I don't know what effect this bias would have on ADEV).

- Dave

On Mon, Mar 16, 2015 at 10:15 AM, James via time-nuts time-nuts@febo.com
wrote:

 Hi All,

 I'm in the process of getting a better counter, but at present I'm using
 my TTi TF930 counter.

 For those who don't know it, it is a reciprocal counter which should be
 continuous, it counts periods in terms of its internal 50MHz clock which
 I've locked to an external 10MHz reference.

 There are 4 gate times available, 0.3 secs, 1 sec, 10 secs and 100 secs.

 These correspond to 7, 8, 9 and 10 digits.

 I've been experimenting with using a single mixer (mini circuits ZAD+)
 along with a 1MHz low pass filter and appropriate attenuators to measure
 Alan Deviation (using my own software).

 My set up is a 10MHz reference source (MV89A which I've approximately set
 using a 10kHz GPS signal).

 The reference is used as the external reference for an Agilent 33522A
 arbitrary waveform generator.

 The 33522A generates an 9.10 MHz (10MHz - 90Hz) sine wave at 300mVpp
 to the mixer and the mixer is also fed by the 10MHz reference output of the
 33522A via an attenuator to get it to roughly the same level.

 The second output of the 33522A generates a 10MHz square wave as a
 reference for the counter (the counter requires quite a high reference
 signal and the reference out of the 33522A is too low a voltage to be used
 directly).

 I initially ran this with a gate of 1 second and the LOG10(ADEV) curve
 drops linearly vs LOG10(tau) but then curves back up again. (I tried many
 variants such as using period rather than frequency and so on.)

 But when I set the gate time to 10 seconds or 100 seconds then I get both
 lower curves and ones that no longer curve upwards.

 The attached pdf shows the three curves on the same graph.

 What puzzles me is that the counter at longer gates is only averaging to
 get more digits so the difference must come down to quantization in terms
 of the number of digits that are passed to the computer over the USB/RS232
 link.

 I find it rather puzzling.

 James






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Re: [time-nuts] Greenwich Timekeeping

[Dave Martindale]

I wish it was coming to Canada.  But according to
http://www.sourcewire.com/news/85588/ships-clocks-stars-exhibition-in-greenwich-ends-sunday-january-4#.VRN-O_nF-uM,
it is heading to two sites in the USA (Folger Shakespeare Library in
Washington DC and Mystic Seaport Museum in Connecticut) plus the Australian
National Maritime Museum.

Perhaps a trip to Conecticut is in order this fall ...

- Dave

On Wed, Mar 25, 2015 at 7:39 PM, Tom Harris celephi...@gmail.com wrote:

 The public exhibition for this conference Ships, Clocks and Stars: The
 Quest for Longitude is apparently coming to the colonies (Canada 
 Australia) this year, so us colonials might get a chance to feast on the
 Harrison timepieces in all their glory. True clock p**n.


 Tom Harris celephi...@gmail.com

 On 26 March 2015 at 03:27, Tom Van Baak t...@leapsecond.com wrote:

  For those of you near London with an interest in Greenwich, Harrison, and
  pendulum clocks there's an event on April 18 that might be worth your
 time.
 
  Harrison Decoded: Towards a Perfect Pendulum Clock
  http://www.rmg.co.uk/whats-on/events/harrison-decoded
 
 
 http://www.rmg.co.uk/sites/default/files/harrison_decoded_draft_programme_250215-3.pdf
 
  /tvb
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Re: [time-nuts] Striking change in iPhone time accuracy with 8.2

[Dave Martindale]

Hmm.  I'd say that the time setting accuracy may have improved, but the
timekeeping accuracy still isn't wonderful.

I just checked my iPhone, using the Emerald Time app to display the
difference between iOS time and NTP time.  The local time was 850 ms fast.
Then I went to Settings-General-Date and Time and turned Set
Automatically off, then back on again.  This seems to have forced the
phone to resync its local time, and now the error is zero (less than 1 ms).

I also have an iPad which had been configured not to set the time
automatically.  It was 2.5 seconds fast.  When I turned automatic setting
on, it reset its local time to within 2 ms of correct.

So the setting appears to be nice and accurate.  But the iPhone, which has
been in automatic time set mode ever since the iOS update 3 weeks ago,
was nearly one second off.  I don't know how often iOS does a time sync, so
I don't know how long it took to drift by that much.  This amount of error
does suggest that it only periodically resets itself to the correct time,
without trying to correct the local oscillator to provide continuously
accurate time (like using NTP would do).

- Dave

On Tue, Mar 31, 2015 at 11:59 PM, Anthony G. Atkielski 
anth...@atkielski.com wrote:

 Has anyone else noticed a dramatic improvement in the accuracy of time
 of day on iPhones and iPads since the release of iOS 8.2? The accuracy
 used to be only plus or minus 2 or 3 seconds, now it is about 100
 times better, usually a few tens of milliseconds. I figure Apple might
 have finally paid some attention to accurate time of day with 8.2,
 possibly because of the Apple Watch. It's a pleasing improvement, I
 hope it's permanent.

 --
 Anthony

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Re: [time-nuts] Measuring frequency rather than tuning crystal

[Dave Martindale]

The TF930/960 does have a calibration procedure that is performed from 
the front panel.  Basically, you feed it a stable input from any known 
source (so both 1 Hz and 10 MHz from a GPSDO should work) and then 
adjust until the displayed frequency agrees with the known input 
frequency.  The resolution of this setting is quite a bit better than 
the stability of the TCXO in the box.


Now, this process could occur either by actually adjusting the frequency 
of a VCTCXO in the box using a DAC, or by changing a calibration 
constant stored in the memory of the device.  I suspect it's actually 
the former, because the instructions say that the adjustment path has a 
low-pass filter that you need to allow to settle.  This wouldn't be 
necessary if the calibration simply changed a stored number.


Dave

On 27/02/2015 15:08, Paul Alfille wrote:

I don't think your TTi TF930 has a GPS input to calibrate against, based on
a quick perusal of the data sheet. I would guess that the calibration
constants are thus fixed from the factory (including temperature
coefficients).


On Thu, Feb 26, 2015 at 3:36 PM, James via time-nuts time-nuts@febo.com
wrote:


I presume that this is what my TTi TF930 does. Calibration is closed box
so I guess the TCXO is free running and the micro inside just uses
calibration constants.

James








-Original Message-
From: Paul Alfille paul.alfi...@gmail.com
To: Discussion of precise time and frequency measurement 
time-nuts@febo.com
Sent: Thu, 26 Feb 2015 19:02
Subject: [time-nuts] Measuring frequency rather than tuning crystal


I have a couple of HP 5370s with the beaglebone brain transplant. They
come
with a nice 10811 that has a little adjustment screw.

Testing against a
Thunderbolt or KS-24361 the 5370 is off by less than 1Hz.

I know the
traditional method would be to adjust the crystal slowly and
make careful
measurements, but since I have a fancy computer in there, I
wonder if I could
just adjust the frequency in software. 64-bit floating
point numbers should
have sufficient accuracy. All reported measurments
would be corrected for the
actual reference frequency.

Basically, I'd have a 1000.226 Hz internal
reference.

In fact, could I connect the beaglebone to a a GPS 1 pps source
and make
this a GPS-disciplined-software-corrected oscillator.

So my
question is is this a known technique? The discipline feedback
circuit seems a
little different, I'd adjusting for drift and offset, but
not the gain of
control-oscillator
linkage.
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Re: [time-nuts] Measuring frequency rather than tuning crystal

[Dave Martindale]

Here is a quote from the TF930/TF960 Service Guide, in the section on
calibrating the internal TCXO:

Set the Measurement Time to 1s and repeat the process. The adjustment per
step is now a decade smaller and multiple presses may be needed. The
measurement restarts after each set of key presses. It will take a few
seconds for the reading to stabilise because of the settling time of a
filter on the control voltage. Aim to be within about 0.5Hz and then move
to the next step.

The reference to the control voltage strongly suggests that it is
actually adjusting the timebase frequency via the frequency control input,
not adjusting a numerical constant.  We know that the TCXO is actually a
VCTCXO, because it can be phase locked to an external reference.  And we
know it's actually phase locking the internal reference when an ext. ref.
is supplied, not merely substituting the external reference in place of the
internal one, because the manual says that the external reference must be a
high-accuracy 10 MHz signal - it is not possible to use a different
reference frequency.  (There is more detail - see the External Reference
section of the 930 or 960 manual).

- Dave

On Fri, Feb 27, 2015 at 4:23 PM, Dave Martindale dave.martind...@gmail.com
wrote:

 The TF930/960 does have a calibration procedure that is performed from the
 front panel.  Basically, you feed it a stable input from any known source
 (so both 1 Hz and 10 MHz from a GPSDO should work) and then adjust until
 the displayed frequency agrees with the known input frequency.  The
 resolution of this setting is quite a bit better than the stability of the
 TCXO in the box.

 Now, this process could occur either by actually adjusting the frequency
 of a VCTCXO in the box using a DAC, or by changing a calibration constant
 stored in the memory of the device.  I suspect it's actually the former,
 because the instructions say that the adjustment path has a low-pass filter
 that you need to allow to settle.  This wouldn't be necessary if the
 calibration simply changed a stored number.

 Dave


 On 27/02/2015 15:08, Paul Alfille wrote:

 I don't think your TTi TF930 has a GPS input to calibrate against, based
 on
 a quick perusal of the data sheet. I would guess that the calibration
 constants are thus fixed from the factory (including temperature
 coefficients).


 On Thu, Feb 26, 2015 at 3:36 PM, James via time-nuts time-nuts@febo.com
 wrote:

  I presume that this is what my TTi TF930 does. Calibration is closed box
 so I guess the TCXO is free running and the micro inside just uses
 calibration constants.

 James








 -Original Message-
 From: Paul Alfille paul.alfi...@gmail.com
 To: Discussion of precise time and frequency measurement 
 time-nuts@febo.com
 Sent: Thu, 26 Feb 2015 19:02
 Subject: [time-nuts] Measuring frequency rather than tuning crystal


 I have a couple of HP 5370s with the beaglebone brain transplant. They
 come
 with a nice 10811 that has a little adjustment screw.

 Testing against a
 Thunderbolt or KS-24361 the 5370 is off by less than 1Hz.

 I know the
 traditional method would be to adjust the crystal slowly and
 make careful
 measurements, but since I have a fancy computer in there, I
 wonder if I could
 just adjust the frequency in software. 64-bit floating
 point numbers should
 have sufficient accuracy. All reported measurments
 would be corrected for the
 actual reference frequency.

 Basically, I'd have a 1000.226 Hz internal
 reference.

 In fact, could I connect the beaglebone to a a GPS 1 pps source
 and make
 this a GPS-disciplined-software-corrected oscillator.

 So my
 question is is this a known technique? The discipline feedback
 circuit seems a
 little different, I'd adjusting for drift and offset, but
 not the gain of
 control-oscillator
 linkage.
 ___
 time-nuts mailing
 list -- time-nuts@febo.com
 To unsubscribe, go to
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 instructions there.


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Re: [time-nuts] Looking for advice to get a submillisecond setup

[Dave Martindale]

Standalone receivers don't have to be expensive.  Take a look at the GPS 
receiver modules at sparkfun.com.  They are under $100 (some way under), 
and some either require or can take an external antenna, and they 
provide 1 PPS output.  Garmin themselves sells receiver boards without 
integrated antennas.


Now, they are navigation not timing receivers, so the 1 PPS accuracy is 
likely only a microsecond or so, not in the nanosecond range. But that's 
plenty for NTP.  And because they are recent receiver designs, they have 
higher sensitivity and faster acquisition than older receivers.  Some 
support WAAS corrections.


-Dave

On 20/02/2015 10:25, Jim Lux wrote:



And yes, a gps antenna needs a good view of the sky, but the receiver
itself can be 100+ meters away from the antenna


I think you're getting into receivers that are well into the hundreds 
of dollars range, if bought new.


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Re: [time-nuts] Once again about counter calibration

[Dave Martindale]

The problem with using a 1 Hz reference when looking at a nominal 10 MHz
signal is that you will get a stable scope display with no drift when the
input is *any* integer number of cycles/sec.  So 10,000,000 Hz will give a
stable display, but so will 9,999,999 Hz and 10,000,001 Hz.  Unless you
know that your 10 MHz signal is already within 0.5 Hz of the correct
frequency, the drift method is likely to cause you to adjust to the nearest
integer number of Hz, not exactly 10 MHz as you want.

It's better to start out with input and reference that are the same
frequency, or are related by some small integer factor.  So you can compare
a 10 MHz adjustable oscillator to a reference that is 1 MHz or 5 MHz or 10
MHz or 20 MHz.  For a stable scope trace, connect the lower of the two
frequencies to the scope trigger input, and the higher frequency to the
scope waveform input.  Then adjust for zero drift.

Also, use an analog oscilloscope if you have one (or a digital scope with a
high waveform update rate).  An analog scope will clearly show a high drift
rate as a smeared waveform, so you will know that you need to keep
adjusting the frequency trimmer and (probably in which direction).  With a
low-cost digital scope, you can get beat frequencies between the drift
frequency and the screen update rate that make it appear as if the input
waveform is stationary, when it fact it is drifting rapidly.

- Dave

On Sat, Apr 25, 2015 at 11:12 PM, d0ct0r t...@patoka.org wrote:



 I tried to use 1PPS as Ext. trigger for the oscilloscope. I was able to
 stabilize signal movement. Then I tried to calibrate OCXO. However its
 appeared out of range (I reach end of potentiometer limit but counter still
 shows that OCXO is out of 10Mhz). Which kind of suspicious.
 Then I decide to disassemble my project to take pure 10Mhz directly from
 GPSDO to measure OCXO signal. Its read totally different frequency value
 now. So, using 1PPS didn't work for me. I tried using that GPSDO 10 Mhz as
 Ext. Trigger. And now I got much better result. I was able to calibrate
 5386A to some extent. But my 5386 has TCXO. So, after few minutes its
 moving out of perfect value. May be I need to wait much longer to
 stabilize oscillator. I am not sure what to expect here.
 Using GPSDO 10 Mhz as REF signal, I was able to calibrate OCXO. And now
 its potentiometer position was nether at its both extremes. The reading on
 5386a (using 10 sec gate) fluctuate from 9.3M to 10.7M.
 Again, may be I need to wait much longer when OCXO will be stable.

 So, I think the best approach will be using 10Mhz GPSDO as ref. signal for
 this counter. In another case, I'll need to wait to warm it up (the manual
 advised only 30 minutes. But I am not sure). And then re-calibrate it. Its
 time consuming.
 I am curious, if its practical to calibrate something like Morion MV89A
 and use it as signal reference for this counter ? Or OCXO still will drift
 out of desired frequency relatively soon ?

 Regards,

 V.P.



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Re: [time-nuts] Once again about counter calibration

[Dave Martindale]

Yeah, I considered saying that.  But if you don't have a TI counter, you
need some way of resetting the divide-by-1e7 chain so the two 1 Hz pulses
are close enough in time that you can see them on the scope at some
reasonably fast sweep rate.  Yes, you can used delayed sweep, but how
stable is the delay?  If you do have a TI counter, then the accuracy of the
counter's time base also factors into the reading (though you don't really
care about absolute timebase frequency, just drift).

A compromise method might be to divide the 10 MHz down to 10 kHz or 1 kHz.
Then the nearest adjacent wrong integer multiple of 1 Hz where the drift
would be zero is 1 part in 10,000 or 1 part in 1000 off the nominal
frequency.  Any decent crystal is unlikely to start out 50 PPM or more off
frequency, and really unlikely to be 500 PPM off frequency, so this mostly
eliminates the wrong ratio problem.  Yet you get one cycle of the scope
input signal every 0.1 or 1 ms, giving a reasonable chance for one of those
edges to drift close enough to the 1 PPS reference to measure the drift at
a fast sweep rate.

- Dave

On Sun, Apr 26, 2015 at 5:58 AM, Tom Van Baak t...@leapsecond.com wrote:

  The problem with using a 1 Hz reference when looking at a nominal 10 MHz
  signal is that you will get a stable scope display with no drift when the
  input is *any* integer number of cycles/sec.  So 10,000,000 Hz will give
 a
  stable display, but so will 9,999,999 Hz and 10,000,001 Hz.  Unless you
  know that your 10 MHz signal is already within 0.5 Hz of the correct
  frequency, the drift method is likely to cause you to adjust to the
 nearest
  integer number of Hz, not exactly 10 MHz as you want.

 One solution to this problem is to divide the 10 MHz to 1PPS and then
 compare the two 1PPS signals, using a 'scope or a TI counter.

 The horizontal sweep of your 'scope and your patience will determine the
 resolution of the measurement. For example, at 1 ns/div you can easily
 resolve a 1e-11 frequency difference within a minute.

 /tvb

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Re: [time-nuts] time-nuts Digest, Vol 130, Issue 27

[Dave Martindale]

Which altitude do you have the Thunderbolt set up to report?

If you have the datum set to WGS-84, the Thunderbolt can report either HAE
(height above ellipsoid) or MSL (height above the geoid model) in its
serial output.  The choice is controlled by bit 2 of byte 0 of the 0x35
command packet.  This can be stored in EEPROM, which determines the
power-up default.

HAE is mathematically simpler to calculate but bears only an approximate
relationship to actual sea level.  MSL requires some sort of table (inside
the GPS receiver) to specify the geoid model, but since it's a fit to the
actual Earth, the altitude is more likely to agree to what you think of as
altitude.

Many GPS receivers provide a choice of which altitude they report in their
output stream, so when comparing two receivers you need to check that both
the datum and the HAE/MSL altitude choices are configured the same.

This should not have any effect on timing.  The GPS receiver knows where it
is in Cartesian coordinates in all cases.  Your choice of map datum
controls the conversion to latitude and longitude that the receiver
reports, while the choice of HEA/MSL controls the conversion to reported
altitude, but these choices should affect this output conversion only.

- Dave


  On May 18, 2015, at 2:34 AM, Demian Martin demianm@gmail.com
 wrote:
 
  I have 2 GPSDO's. A Thunderbolt and an Arbiter 1083A. The Arbiter is old
 but
  it works fine (and has a Wenzel 5 MHz streamline oscillator in it). It
 has
  the 1995 firmware issue, and I could get new firmware for it ($$) but I'm
  not using it as a clock, just a frequency source.
 
 
 
  I just moved and have re-setup both. They share an antenna. I got both
 to do
  a self survey. The Arbiter was really close to what Google maps indicate
 is
  my location. The Thunderbolt was about the same except it has me
  underground. The arbiter has the height as +30M. The Thunderbolt as -6M.
  What setting do I have wrong in the Thunderbolt? Would it affect the
  operation as a frequency standard in any way?
 
 
 
 
 
  Demian Martin
 
  San Leandro, CA 94577

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Re: [time-nuts] Leap Second results: cheap GPS/1PPS receivers

[Dave Martindale]

It seems odd that the Garmin receiver got it wrong.  The Garmin GPS-20 and
-25, which I think are both older than the 18x, get it correct.  The GPS-20
is so old it is a single-channel receiver, the GPS-25 is 12-channel but
still 5 V power.

GPS-20, June 1998:
$GPRMC,235959,A,4913.2184,N,12305.9266,W,0.0,199.2,300697,020.3,E*62
$GPGGA,235959,4913.2184,N,12305.9266,W,1,05,2.1,34.3,M,-17.6,M,,*40

$GPRMC,235960,A,4913.2182,N,12305.9267,W,0.0,199.2,300697,020.3,E*6F
$GPGGA,235960,4913.2182,N,12305.9267,W,1,05,2.1,34.2,M,-17.6,M,,*4C

$GPRMC,00,A,4913.2180,N,12305.9266,W,0.0,199.2,010797,020.3,E*64
$GPGGA,00,4913.2180,N,12305.9266,W,1,05,2.1,33.7,M,-17.6,M,,*46

GPS-25, December 1999:
$GPRMC,235959,A,4913.2302,N,12305.9332,W,000.0,169.8,311298,019.6,E*6F
$GPGGA,235959,4913.2302,N,12305.9332,W,1,04,2.9,105.0,M,-17.6,M,,*75

$GPRMC,235960,A,4913.2303,N,12305.9333,W,000.0,169.8,311298,019.6,E*65
$GPGGA,235960,4913.2303,N,12305.9333,W,1,04,3.1,105.0,M,-17.6,M,,*76

$GPRMC,00,A,4913.2304,N,12305.9333,W,000.0,169.8,010199,019.6,E*69
$GPGGA,00,4913.2304,N,12305.9333,W,1,04,3.1,105.0,M,-17.6,M,,*7A


On Wed, Jul 1, 2015 at 7:34 PM, Kasper Pedersen time-n...@kasperkp.dk
wrote:

 On 07/01/2015 05:23 PM, Tom Van Baak wrote:
  I logged NMEA from three cheap ($15-$50) GPS/1PPS receivers, the kind
 popular with hobbyists: parallax(good), reyax(good), adafruit(bad).

 
  3) Adafruit Ultimate GPS Breakout
  http://www.adafruit.com/products/746

 
  If someone else has data from this model receiver, please let me know.
 

 I have:
  - MC-1010 (MTK3339, same chipset and code as the adafruit one)
  - GPS-1513R (Venus 624) -- FUN!
  - LTE-Lite
  - old GPS18x


 The MTK3339 with the same (standard) firmware is also used in the
 MC-1010. I have output from the 28th and ahead. Same behaviour.

 $GPGGA,235958.000,5610.4160,N,00929.5793,E,1,10,0.80,84.8,M,43.3,M,,*5E
 $GPRMC,235958.000,A,5610.4160,N,00929.5793,E,0.01,171.62,300615,,,A*66

 $GPGGA,235959.000,5610.4160,N,00929.5793,E,1,10,0.80,84.8,M,43.3,M,,*5F
 $GPRMC,235959.000,A,5610.4160,N,00929.5793,E,0.01,171.62,300615,,,A*67

 $GPGGA,235959.000,5610.4160,N,00929.5793,E,1,10,0.80,84.8,M,43.3,M,,*5F
 $GPRMC,235959.000,A,5610.4160,N,00929.5793,E,0.01,171.62,300615,,,A*67

 $GPGGA,00.000,5610.4160,N,00929.5793,E,1,10,0.80,84.8,M,43.3,M,,*5E
 $GPRMC,00.000,A,5610.4160,N,00929.5793,E,0.02,171.62,010715,,,A*66

 $GPGGA,01.000,5610.4160,N,00929.5793,E,1,10,0.80,84.8,M,43.3,M,,*5F
 $GPRMC,01.000,A,5610.4160,N,00929.5793,E,0.01,171.62,010715,,,A*64



 But, SkyTraq venus 624 (RF Solutions GPS-1513R) is much more fun. It
 backsteps one minute(!), in addition to the other 'features' it has.

 $GPGGA,235958.187,5610.4163,N,00929.5757,E,1,11,0.8,84.6,M,41.0,M,,*65
 $GPRMC,235958.187,A,5610.4163,N,00929.5757,E,000.0,308.5,300615,,,A*6F

 $GPGGA,235959.187,5610.4163,N,00929.5757,E,1,11,0.8,84.6,M,41.0,M,,*64
 $GPRMC,235959.187,A,5610.4163,N,00929.5757,E,000.0,308.5,300615,,,A*6E

 $GPGGA,235900.000,5610.4163,N,00929.5757,E,1,11,0.8,84.6,M,41.0,M,,*66
 $GPRMC,235900.000,A,5610.4163,N,00929.5757,E,000.0,308.5,300615,,,A*6C

 $GPGGA,00.187,5610.4163,N,00929.5757,E,1,11,0.8,84.5,M,41.0,M,,*66
 $GPRMC,00.187,A,5610.4163,N,00929.5757,E,000.0,308.5,010715,,,A*6C

 $GPGGA,01.187,5610.4163,N,00929.5757,E,1,11,0.8,84.5,M,41.0,M,,*67
 $GPRMC,01.187,A,5610.4163,N,00929.5757,E,000.0,308.5,010715,,,A*6D



 The Venus on the LTE-Lite, with the updated timing firmware, is sane.
 I also have the 20MHz output timestamped every 5ms, nothing odd happened.

 $GPGGA,235959.000,5610.4155,N,00929.5739,E,2,09,0.9,85.4,M,41.0,M,,*6F
 $GPRMC,235959.000,A,5610.4155,N,00929.5739,E,000.0,000.0,300615,,,D*66

 $GPGGA,235960.000,5610.4155,N,00929.5739,E,2,09,0.9,85.4,M,41.0,M,,*65
 $GPRMC,235960.000,A,5610.4155,N,00929.5739,E,000.0,000.0,300615,,,D*6C

 $GPGGA,00.000,5610.4155,N,00929.5739,E,2,09,0.9,85.4,M,41.0,M,,*6E
 $GPRMC,00.000,A,5610.4155,N,00929.5739,E,000.0,000.0,010715,,,D*64


 Old Garmin GPS18x did the same as the MTK3339:

 $GPRMC,235958,A,5611.0119,N,00932.1092,E,000.0,136.1,300615,002.0,E,D*10
 $GPGGA,235958,5611.0119,N,00932.1092,E,2,10,0.8,41.5,M,41.7,M,,*72

 $GPRMC,235959,A,5611.0119,N,00932.1093,E,000.0,136.1,300615,002.0,E,D*10
 $GPGGA,235959,5611.0119,N,00932.1093,E,2,10,0.8,41.4,M,41.7,M,,*73

 $GPRMC,235959,A,5611.0119,N,00932.1094,E,000.0,136.1,300615,002.0,E,D*17
 $GPGGA,235959,5611.0119,N,00932.1094,E,2,10,0.8,41.3,M,41.7,M,,*73

 $GPRMC,00,A,5611.0120,N,00932.1094,E,000.0,136.1,010715,002.0,E,D*1F
 $GPGGA,00,5611.0120,N,00932.1094,E,2,10,0.8,41.2,M,41.7,M,,*79

 $GPRMC,01,A,5611.0120,N,00932.1094,E,000.0,136.1,010715,002.0,E,D*1E
 $GPGGA,01,5611.0120,N,00932.1094,E,2,10,0.8,41.2,M,41.7,M,,*78


 /Kasper Pedersen
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 and 

[time-nuts] Large clock display from NMEA input? (Should understand leap second).

[Dave Martindale]

Tomorrow evening, I'm going to a leap second barbecue.  The barbecue itself
was the idea of a friend, but I'm bringing the equipment to show the leap
second.

My main setup is a Thunderbolt, Lady Heather running on a PC laptop, and a
serial to USB converter.  It's all working sitting here on a desk this
evening, so the only thing I can't test in advance is the leap second
itself.  I haven't had the Thunderbolt running during a leap second before,
but there is a YouTube video showing the June 2012 leap second as handled
by a Thunderbolt and Lady Heather, so I'm assuming all will work as
expected.

Never one to trust a single piece of hardware completely, I want to bring a
backup.  I have an old Garmin GPS-25 board mounted in a box with power
supply and RS-232 level converters, so I want to bring it too. I have
watched a leap second previously on the GPS-25, so I know it handles the
event properly.  But the GPS-25 is NMEA output so it won't work with Lady
Heather.  I need something else to display a digital clock that everyone
can see, from a NMEA data stream.

VisualGPS displays a bunch of interesting stuff, but not time.  U-center
from u-blox displays UTC as both analog and digital clock, and the analog
clock can be made as large as you have screen space for.  Does anyone know
what it does with a leap second?

Are there other programs I should look at?

- Dave
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Re: [time-nuts] 60Hz line data

[Dave Martindale]

It's not just synchronous-motor clocks that use line frequency as a time
reference.  I have a Heathkit alarm clock that counts cycles of line
frequency as its timebase.  I think that was common in the early
generations of NMOS clock chips.  The clock does have a backup oscillator
(powered by a 9 V battery) for use when line voltage disappears, but its
accuracy is horrible.  I think it's an RC oscillator, and in a power
failure of a few hours it will accumulate minutes of time error.

So a bunch of people with analog and digital clocks from that era are
likely to notice the drift, particularly at 20 minutes/year.

When did 32 kHz crystals get cheap enough that line-powered clocks started
using them as a time reference instead of counting line cycles?

- Dave

On Sun, Jul 26, 2015 at 2:25 PM, Bill Byrom t...@radio.sent.com wrote:


 60Hz Stability on Power Grid Going Away?

 http://www.radiomagonline.com/deep-dig/0005/60hz-stability-on-power-grid-going-away/33527

 NERC Frequency Response Standard Background Document

 http://www.nerc.com/comm/oc/rs%20landing%20page%20dl/related%20files/bal-003-1_background_document_clean_20121130.pdf

 It  appears from various comments that with no manual time correction,
 the accumulated time error in the East Interconnection will typically
 gain 20+ minutes/year. The West will gain 8 minutes/year and ERCOT
 (Texas area) will gain 2 minutes/year.

 http://www.ercot.com/content/meetings/rms/keydocs/2011/0518/03_manual_time_error_correction_elimination_field_trial.doc

 So don't trust an AC synchronous motor clock in North America.

 --
 Bill Byrom N5BB


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Re: [time-nuts] UPS for my time rack

[Dave Martindale]

How did you find the units that will act as a UPS, without buying
everything on the market and testing them?

I just checked all of those bricks in our house, and none will do it.
There are a couple of PNY units that do not provide output power until a
button is pressed, and don't charge until input power is connected while in
idle mode.  Then there are Tp-Link and Mophie units that switch on the
output automatically when a load is connected (or perhaps the output is
just always powered), but which disable the output and switch to charge
mode when input power is provided.  None of them seem able to pass through
5V power without discharging.

- Dave

On Tue, Oct 13, 2015 at 2:07 PM, Tom Van Baak  wrote:

>
> Recently, as some of my gear works from 5 VDC, those ~2600 mAh mobile
> phone USB backup power bricks make an excellent mini-UPS. The ideal models
> are those without LEDs or on/off buttons so they discharge and charge/float
> seamlessly without manual intervention, even if fully drained.
>
> Multiple units can be placed in series for additional, if slightly
> inefficient, capacity. A good self-test is:
>
> http://leapsecond.com/images/perpetual-USB-power.jpg
>
> /tvb
>
>
>
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Re: [time-nuts] UBLOX LEA-5T Programming?

[Dave Martindale]

(Long-term members of the list can skip this; you've seen it many times 
before.  But it sounds like Clint is new, and could use some basic 
explanation.  I was in his position once too).


It sounds like you are assuming that the GPS receiver's internal oscillator is 
locked to GPS time.  In most cases, it isn't - it's a free-running local 
oscillator.  So its frequency isn't terribly accurate.  The GPS receiver, as 
part of its operation, can determine what the local clock frequency is and 
compensate for it.  For the 1 PPS output, the receiver can calculate which 
local clock edge is closest to being the correct location for the next 1 PPS 
pulse, and arranges to change the output state at that time.  But the divisor 
between the internal clock and the 1 PPS output is not constant - it is 
adjusted as necessary to place the 1 PPS as close as possible to the correct time.


For example, suppose the local oscillator is nominally 10 MHz, but it is 
actually 10 PPB fast.  If it was simply divided by 1e7 to get the 1 PPS, the 1 
PPS would also be 10 PPB fast.  So the GPS receiver will arrange to (on 
average) divide by 10,000,000 for 9 seconds out of every 10, but divide by 
10,000,001 every 10th second.  This slows the PPS, on average, by one extra 
oscillator cycle in every 100 million, compensating for the long-term error.  
But now some "1 PPS" periods are actually 100 ns longer than others.  The very 
best the GPS receiver can do at keeping the 1 PPS "on time" as well as "on 
frequency" is to always place the 1 PPS somewhere within 50 ns of the correct 
time.  With this example, the error will drift from 50 ns late to 50 ns early 
over a span of 10 seconds, then abruptly jump to 50 ns late again due to the 
extra-cycle 1 PPS period.  So the time error looks like a sawtooth when graphed.


If you have a timing-grade GPS, the receiver will generally tell you the 
residual error of each 1 PPS pulse, and you can compensate for that when 
comparing an external oscillator to the 1 PPS output. Essentially, it gives 
you a timing reference with a somewhat-random error, but it tells you the 
amount of the error, so you can subtract it out of your calculations.  That's 
easy if you're using a digital PLL to lock another oscillator to the 
(corrected) 1 PPS.  Someone was even talking about designing a delay line to 
remove the sawtooth error from the 1 PPS in hardware.  If you don't do one of 
these things, the 1 PPS output has a lot of jitter.  (And it doesn't 
necessarily average out in 10 seconds, like in the example above. If the local 
oscillator is close to the correct frequency, you can get 1 PPS outputs that 
are on one side or the other of "correct" for hundreds or thousands of 
seconds.  The phenomenon is called "hanging bridges" from the way they look on 
a graph).


- Dave

On 09/10/2015 10:16, Clint Jay wrote:

I am still learning and want to understand, if the PPS is good then why is
the programmable output bad, as I understand it thus far, the PPS is
derived from the same clock source or have I got that badly wrong?




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Re: [time-nuts] New wrist watch

[Dave Martindale]

Two data points for one watch:
When I bought a Casio PAW-1300, it was about 20 seconds fast.  It said that
it had last synced on September 24, but that information does not include
the year.  It was now June 10, so it had been running without a radio sync
for at least 9 months (though it could have been 9 months plus 1 year, or
plus 2 years...).  If we assume the delay is only 9 months for 20 seconds
of error, that's a error of about 2.8 seconds/month or about 1 PPM.

A year later, the same watch got stored in a drawer where there was no
light and poor radio reception.  After 26 days without a successful radio
sync, it had gained 2 seconds.

(On the other hand, the watch does *not* handle a leap second when the leap
second actually occurs.  It simply keeps counting, so it ended up being 1
second fast after the recent June 30 leap second.  It was correct the next
morning, after its usual overnight sync to Colorado.)

I normally leave the watch on the window ledge of a window approximately
facing Colorado (I'm near Toronto).  It gets lots of light to keep the
battery charged, and reliably syncs every night.  It has become my master
time source that I sync all my other watches to when adjusting them.
 (Someday I need to build a time display for one of my GPS receivers, but
the Casio works well enough).

- Dave

On Mon, Jul 6, 2015 at 6:45 PM, D W watsondani...@gmail.com wrote:

 With my new found interest in time nuttiness I thought I should upgrade to
 a decently accurate watch. I had some features I was looking for and
 settled on a Casio Wave Ceptor. My second choice was an Eco Drive, but the
 Casio had the right mix of features at a good price.

 As I was sitting outside reading the manual after buying it, I laid it
 flat on the table and started a manual sync to WWVB. The UI is pretty
 intuitive for having so few buttons and indicators. It quickly told me that
 it had found a stable signal, and about six minutes later it was synced.
 Pretty cool.

 Anyone know what the drift is like in this watch if it can't find the
 signal for several days/weeks? I would hope that actual performance is a
 little better than the +/- 15 sec per month stated in the manual. I should
 trap it in a faraday bag for a while to test it...

 Dan
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Re: [time-nuts] Mechanical clock sound pickup circuit

[Dave Martindale]

Someone is in the process of writing open-source watch timing software.
You may want to look into it.

It was announced here:
http://forums.watchuseek.com/f6/open-source-timing-software-2542874-post21977314.html#poststop

It contains these links:
First the goodies. Here are Windows binaries
http://ciovil.li/tg.zip
and here is the full source code
https://github.com/vacaboja/tg

Apparently this software is better at dealing with noisy signals from
microphones than Biburo.  Since it's open source, you can see what it's
doing internally.  It expects an analog input, and does its own filtering
to find the interesting edges within the sound of each tick.

The precision with which you can time events is likely to be limited by the
frequency response of your sensor and the amplifier.  If that's limited to
20 kHz, a standard PC sound card is adequate.  For up to 80 kHz or so, you
can buy a relatively inexpensive USB "audio interface" that digitizes at
192 kHz (typically 24 bit resolution).  At somewhat higher cost, you can
get professional audio interfaces that accept an external clock source.

- Dave


On Fri, Dec 11, 2015 at 1:44 PM, Andrea Baldoni 
wrote:

> Hello!
>
> I decided to do some experiments with mechanical clocks, so I worked a
> little
> on picking up escapement ticking sound, with the idea of processing it and
> obtaining a "clean" digital pulse to feed a counter.
>
> So far, I have not yet been able to find the best way to obtain a digital
> pulse,
> but I have already built the preamp for the piezoelectrick pickup, that
> I used to feed the mic input of a PC sound card for spectrum analysis.
>
> The timing could eventually be done in software because the whole idea of
> measuring watches by picking up their noise almost surely doesn't allow
> high
> resolution anyway, but I will plan to try hardware solutions as well in the
> future. I hope to be able to measure the jitter of the clock, but it will
> be
> very hard.
>
> In the meantime, with the free software Biburo you can download here
>
> http://tokeiyade.michikusa.jp
>
> you can regulate your wrist watch.
>
> Best regards,
> Andrea Baldoni
>
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[time-nuts] Visiting Greenwich

[Dave Martindale]

I am in London England at the moment, playing tourist with the rest of my
family.  I want one day to be a visit to the National Maritime Museum at
Greenwich, which includes the Royal Observatory Greenwich.  I am
particularly interested in seeing Harrison's H1 through H4, plus other
high-precision mechanical timekeepers (pendulum clocks, etc).

I know they are at the NMM - their web site shows some of them.  But where
are they located on the site?  The NMM has a large main building down near
the Thames, while the Royal Observatory and related buildings are on the
top of a hill further inland in Greenwich Park.  Are the chronometers and
other precision timekeepers on display somewhere in the Royal Observatory,
or down in the main NMM building?  I've spent an hour or two browsing web
sites without finding this particular bit of information.

I figure there must be list members who have visited the NMM, and know
where the precision timekeepers are actually displayed.

Thanks,
Dave
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Re: [time-nuts] Visiting Greenwich

[Dave Martindale]

Wouldn't that be "un pied dans chaque hemisphere" in France?

I visited the Greenwich observatory a number of years ago, but it was after
5 PM and all of the exhibits were closed for the day.  So we only saw the
repeater clock and the meridian line.  One interesting fact:  A GPS
receiver will not agree with the line set into the concrete about where
zero degrees of longitude is located.  The GPS prime meridian is somewhere
nearby, within the park, but not at the marked line.

An explanation for this (that I found at the time) is that the line in the
ground at the observatory is defined as zero longitude in whatever geodetic
ellipsoid and datum the British were using at the time.  The GPS zero
longitude line is at zero in WGS84.  Apparently WGS84 is defined to agree
with the older British datum in longitude *at the equator*, but the two
ellipsoids use different models of the earth's axis and so the two
zero-longitude meridians do not agree at Greenwich's latitude of ~50 N.

Google found this more recent article:
http://www.thegreenwichmeridian.org/tgm/articles.php?article=7 that has
more interesting (and more detailed) information about the difference in
the prime meridian definitions.

Dave

On Tuesday, 5 July 2016, jimlux  wrote:

>
> One must, of course, take a picture with one foot in each hemisphere.
> (Unless, you would follow the French, in which case, the Paris meridian is
> the only true meridian, and then you'd have one meter in each
> hemisphere...
>
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Re: [time-nuts] Visiting Greenwich

[Dave Martindale]

Hmm.  When I was there yesterday I didn't see any "No Photography" signs,
so I photographed lots of the exhibits, including the four Harrisons . I
used flash, so I wasn't the least bit stealthy, and one of the staff was
only a few feet away.  Maybe they no longer care?

Dave

On Wednesday, 6 July 2016, Morris Odell  wrote:

>  I can recommend the climb up the hill at Greenwich to anyone - it's
> definitely worth the effort. They didn't allow photography of the Harrison
> clocks but I did manage to sneak one or two before the minder got to me :-)
>
> Morris
> Melbourne, Australia
>
>
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Re: [time-nuts] 1PPS to 32.768 khz

[Dave Martindale]

If the "big digital clock" doesn't display the time with fractional-second
precision, then it only needs to be updated at 1 Hz, which can be done with
the 1 PPS directly.  Consider replacing the 32 kHz crystal, divider chain,
and microprocessor with a new microcontroller that takes 1 Hz input and
drives the display in the same way.

For an extra bonus, use a microcontroller with a serial port, and connect
the GPS receiver serial output to the serial port on the micro.  Then you
can decode the serial data stream from the GPS, and automatically set the
clock to the correct time after a power failure - something the original
clock could not do.  As a double bonus, make the clock display leap seconds
correctly when they happen.

- Dave

On Tue, Oct 18, 2016 at 10:03 PM, Lee - N2LEE via time-nuts <
time-nuts@febo.com> wrote:

>
> 1. Does anyone know of a device that will take a 1PPS GPS timing signal
> and generate a 32.768 kHz sine wave output ?
> I have big digital clock that uses an 8 bit micro processor and an
> external 32.768 crystal. Obviously the external crystal is
> awful for accuracy.
>
>
>
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[time-nuts] Updating Garmin GPS 25 LP after GPS week rollover

[Dave Martindale]

Recently, I was invited to an event to celebrate the addition of a leap
second.
I thought I would provide the entertainment by bringing a suitable GPS
receiver
plus a laptop running Lady Heather.  I had done this before, so I thought it
would be easy, but a whole collection of things went wrong, and I never did
get
everything working in time for the leap second.  (A story for another day).

Since Lady Heather 5.00 was out, I thought I would try using the new
version.
Since LH now supports NMEA GPS receivers, I decided to dig out my old GPS 25
LP.  Though not a timing receiver (no fixed location mode), it does have a 1
PPS output and understands leap seconds, so it should be good enough for the
intended demonstration.

After editing heather.cfg for the serial port, bit rate, and receiver type
(I
didn't try using autodetect), LH started up and began displaying data.  One
of
the things that was obviously wrong was the displayed date: sometime in May
2027.  A quick look at the raw NMEA data (any terminal emulator will do, one
nice thing about NMEA data) showed that the GPS 25 itself thought the date
was
in May 1997, exactly 1024 weeks in the past.  The NMEA output has only a
2-character field for the year, which was thus "97".  And Lady Heather
interprets "97" as 2097, not 1997.  That's why the date was wrong by 100
years
minus 1024 weeks (about 80.4 years).

So yesterday I looked for information about how to update a GPS 25 LP after
a
GPS week rollover.  I didn't find anything on Garmin's web site, but I found
this site instead:
http://www.blackboxcamera.com/pic-osd/GPS25_date_error.htm

Apparently BlackBoxCamera builds video overlay displays, and once upon a
time
they included a GPS 35 as part of their product.  (The 35 is basically a 25
in
a "puck" package).  Users reported seeing wrong dates in 2014, and they
obtained the update procedure from Garmin.  It depends on a Garmin
configuration utility program which is still on their website at
http://www8.garmin.com/support/download_details.jsp?id=925.  So you will
need
that (and a PC to run it on)

The update procedure is still on the blackboxcamera web page for now, but
who
knows how long any web page will remain accessible.  So I have posted the
directions here, to get them archived as part of time-nuts.

   1. Run SNSRCFG (or SNSRXCFG), choose the appropriate model of GPS
   receiver and click OK
   2. Use Comm/Setup, choose the correct com port, choose Auto for baud
   rate and click OK
   3. Use Config/Switch to NMEA mode and click through the pop-ups
   4. Use Comm/Connect (must be successful in order to continue, but a
   connection at a baud rate of 38400 or higher indicates a wiring error)
   5. Use Config/Get Configuration from GPS ( This step is critical. If
   missed the receiver may no longer send the correct data to the video
   overlay )
   6. Use Config/Sensor Configuration, make sure that Phase Output Data is
   not checked (this is called Garmin Binary Output when running SNSRXCFG),
   make any other desired changes and click OK
   7. Use Config/NMEA Sentence Selections, select the desired sentences and
   click OK ( Skip this step if only the date is being reset )
   8. Use Config/Send Configuration to GPS
   9. Use Config/Sensor Configuration and click the Reset NonVol or Erase
   NonVol button, whichever of these is present on the version of
   configuration software you are running
   10. Cycle power to the GPS receiver, re-perform steps 1 through 4 and
   then proceed with step 11
   11. Use View/NMEA Transmitted Sentences and see what date is coming from
   the GPS receiver. If it is still 1024 weeks behind, then follow steps 12
   through 16. (Otherwise, you're done.)
   12. Set your computer's clock ahead 9 years
   13. Use Config/Get Configuration from GPS
   14. Use Config/Send Configuration to GPS
   15. Repeat steps 12 through 14 two more times
   16. Cycle power to the GPS receiver, set your computer's clock to the
   correct date and time, re-perform steps 1 through 4 and proceed with step 17
   17. Use Config/Get Configuration from GP
   18. Use Config/Send Configuration to GPS

---
My own experience with these instructions is that at step 11 the date had
*not*
been updated, so I performed steps 12-15 a total of 3 times as described.
Then
the date was correct.  The update process likely flushes the almanac,
because
it took longer than normal to acquire a first fix after the update (but
still
within 5 minutes or so).

The SNSRCFG software seems to be more recent than the GPS 25 LP.  The 25 LP
manual says nothing about SNSRCFG, but some later Garmin board manuals do
describe the config software and how to use it. (e.g. the Garmin 18X
manual).
The software seems to support the Garmin 10, 10x, 15/15U/15H/15L, 16/17,
16A,
17N, 18PC/LVC, 18(5Hz), and 25/36/36.  So the software and procedures above
may
be able to correct week rollover for any of these GPS receivers.

But it definitely 

Re: [time-nuts] ADEV query Timelab and TICC

[Dave Martindale]

The LTE-Lite User Manual (version 1.3) says:

2.3.7 1 PPS Module outputs
The LTE-Lite SMT Module provides GPS raw 1 PPS CMOS pulse on pin 15 with
sawtooth present, and a clean TCXO-generated, sawtooth-removed, UTC(GPS)
phase-locked 1PPS output on pin 4.

It is the pin 4 output that connects to the 1PPS-OUT jack on the eval
board.  So it is supposed to be cleanly divided down from the TCXO.  (But I
don't think Jackson Labs has published any of the circuitry on the LTE-Lite
module itself).

- Dave

On Mon, Mar 20, 2017 at 2:07 AM, Mark Sims  wrote:

>
> It is also interesting that the LTE GPSDO 1PPS has such a wide range of
> TIE.   A Tbolt / Z38xx GPSDO typically has a TIE in the 1PPS signal of
> around 1 nsec.   The LTE TIE spans over 40 nanoseconds (not including the
> spikes).  It seems like the LTE 1PPS may be from the GPS and not derived
> from dividing down the disciplined oscillator output.
> ___
>
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