[time-nuts] No GPS satellites

[Doug Ronald]

I'm hoping someone can shed some light on my problem receiving any GPS satellites.

I have two TrueTime GPS Time & Frequency Receivers, Model XL-DC. One has a regular crystal oscillator, and the other one has a rubidium oscillator. I have two outdoor GPS antennas with internal LNAs, one a 28 dB gain unit, and the other a 40 dB unit. When either antenna is connected to my Lucent KS-24361, it locks right up and tracks up to 8 satellites. When either of the antennas is connected to the XL-DCs, they just sit there and status : "Looking for GPS satellites".

In the Alarm menu of either XL-DC there is an alarm for Antenna. Both units say "OK" and if I disconnect the antenna they both logically say "Open". So, what is the problem? I can't believe I don't have enough signal, after the Lucent locks-up right away. Is it possible the TrueTime sanctioned antenna has a down converter in it, perhaps placing the GPS signal from L-band to some lower frequency? I would appreciate any info the group might have...

-Doug Ronald
W6DSR

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[Tim Shoppa]

Yes, the XL-DC and other Truetime models had as an option for long cable
runs, a downconverter in the antenna. I don't know how to tell the
difference from part number, but I know the truetimes my employer uses all
have the downconverter option and the option is very common.

Tim N3QE

Post by Doug Ronald
I'm hoping someone can shed some light on my problem receiving any GPS satellites.
I have two TrueTime GPS Time & Frequency Receivers, Model XL-DC. One has a
regular crystal oscillator, and the other one has a rubidium oscillator. I
have two outdoor GPS antennas with internal LNAs, one a 28 dB gain unit,
and the other a 40 dB unit. When either antenna is connected to my Lucent
KS-24361, it locks right up and tracks up to 8 satellites. When either of
"Looking for GPS satellites".
In the Alarm menu of either XL-DC there is an alarm for Antenna. Both
units say "OK" and if I disconnect the antenna they both logically say
"Open". So, what is the problem? I can't believe I don't have enough
signal, after the Lucent locks-up right away. Is it possible the TrueTime
sanctioned antenna has a down converter in it, perhaps placing the GPS
signal from L-band to some lower frequency? I would appreciate any info the
group might have...
-Doug Ronald
W6DSR
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[Bill Hawkins]

Doesn't the DC in the model number mean "down conversion" or something
like that?

Seems to me it did in the obsolete 468-DC GOES time receivers, which had
to down convert to about 1.8 MHz.
Also, the down conversion was more than a simple local oscillator and
mixer. You had to have their antenna to make it work, as the mixer was
in the base of the antenna.

Bill Hawkins


-----Original Message-----
From: Tim Shoppa
Sent: Wednesday, February 25, 2015 7:56 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] No GPS satellites

Yes, the XL-DC and other Truetime models had as an option for long cable
runs, a downconverter in the antenna. I don't know how to tell the
difference from part number, but I know the truetimes my employer uses
all have the downconverter option and the option is very common.

Tim N3QE


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[paul swed]

A fellow time-nut shared the manual for the xl-dc and I downloaded it.
It clearly states that it has a down converter. That was very typical of
these generation receivers. As examples the Odetics and Austrons. It
allowed for very short antenna runs or virtually 0 length antenna runs and
losses. The DC468 goes used the same trick.
Almost always the receivers show up without the dowconverter because those
stay on the roof. Without the down converter the units useless.
I have been lucky in some exploits to use odetics down converters with the
austron and the another approach using older styles semi-integrated
receivers to fake it.
So if you want to experiment there is hope. Though it seems each receivers
a bit different.The older Truetime manuals were pretty good with schematics
and explanations. Unfortunately it looks like the new manual has little to
go on.
Regards
Paul
WB8TSL

Post by Bill Hawkins
Doesn't the DC in the model number mean "down conversion" or something
like that?
Seems to me it did in the obsolete 468-DC GOES time receivers, which had
to down convert to about 1.8 MHz.
Also, the down conversion was more than a simple local oscillator and
mixer. You had to have their antenna to make it work, as the mixer was
in the base of the antenna.
Bill Hawkins
-----Original Message-----
From: Tim Shoppa
Sent: Wednesday, February 25, 2015 7:56 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] No GPS satellites
Yes, the XL-DC and other Truetime models had as an option for long cable
runs, a downconverter in the antenna. I don't know how to tell the
difference from part number, but I know the truetimes my employer uses
all have the downconverter option and the option is very common.
Tim N3QE
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[paul swed]

Boy I ran out to mr google and did a search and now I am wondering if some
versions of the xl-dc just used a plain old GPS antenna. It sure looks like
that could be the case. The manual does say down converter. Maybe it
changed over time.
Regards
Paul
WB8TSL

Post by paul swed
A fellow time-nut shared the manual for the xl-dc and I downloaded it.
It clearly states that it has a down converter. That was very typical of
these generation receivers. As examples the Odetics and Austrons. It
allowed for very short antenna runs or virtually 0 length antenna runs and
losses. The DC468 goes used the same trick.
Almost always the receivers show up without the dowconverter because those
stay on the roof. Without the down converter the units useless.
I have been lucky in some exploits to use odetics down converters with the
austron and the another approach using older styles semi-integrated
receivers to fake it.
So if you want to experiment there is hope. Though it seems each receivers
a bit different.The older Truetime manuals were pretty good with schematics
and explanations. Unfortunately it looks like the new manual has little to
go on.
Regards
Paul
WB8TSL

Post by Bill Hawkins
Doesn't the DC in the model number mean "down conversion" or something
like that?
Seems to me it did in the obsolete 468-DC GOES time receivers, which had
to down convert to about 1.8 MHz.
Also, the down conversion was more than a simple local oscillator and
mixer. You had to have their antenna to make it work, as the mixer was
in the base of the antenna.
Bill Hawkins
-----Original Message-----
From: Tim Shoppa
Sent: Wednesday, February 25, 2015 7:56 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] No GPS satellites
Yes, the XL-DC and other Truetime models had as an option for long cable
runs, a downconverter in the antenna. I don't know how to tell the
difference from part number, but I know the truetimes my employer uses
all have the downconverter option and the option is very common.
Tim N3QE
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[Bob Camp]

Hi

All of these older rack mount “GPSDO” products had a fairly long lifespan compared
to the advances in GPS receivers. When some / most of them first came out, the only practical /proven
way to do timing off GPS was with a downconverter. Without things like serial numbers / date codes it’s
tough to figure out if this sample of box A has anything at all to do with another sample of the same box.
On top of that, these are very low volume products compared to normal HP or Fluke
test gear. It’s unlikely that anybody has a database that tells what is what simply from
the serial numbers or date codes. I’d bet that many of them were built to order and rarely in
groups larger than a few dozen.

Bob

Post by paul swed
Boy I ran out to mr google and did a search and now I am wondering if some
versions of the xl-dc just used a plain old GPS antenna. It sure looks like
that could be the case. The manual does say down converter. Maybe it
changed over time.
Regards
Paul
WB8TSL

Post by paul swed
A fellow time-nut shared the manual for the xl-dc and I downloaded it.
It clearly states that it has a down converter. That was very typical of
these generation receivers. As examples the Odetics and Austrons. It
allowed for very short antenna runs or virtually 0 length antenna runs and
losses. The DC468 goes used the same trick.
Almost always the receivers show up without the dowconverter because those
stay on the roof. Without the down converter the units useless.
I have been lucky in some exploits to use odetics down converters with the
austron and the another approach using older styles semi-integrated
receivers to fake it.
So if you want to experiment there is hope. Though it seems each receivers
a bit different.The older Truetime manuals were pretty good with schematics
and explanations. Unfortunately it looks like the new manual has little to
go on.
Regards
Paul
WB8TSL

Post by Bill Hawkins
Doesn't the DC in the model number mean "down conversion" or something
like that?
Seems to me it did in the obsolete 468-DC GOES time receivers, which had
to down convert to about 1.8 MHz.
Also, the down conversion was more than a simple local oscillator and
mixer. You had to have their antenna to make it work, as the mixer was
in the base of the antenna.
Bill Hawkins
-----Original Message-----
From: Tim Shoppa
Sent: Wednesday, February 25, 2015 7:56 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] No GPS satellites
Yes, the XL-DC and other Truetime models had as an option for long cable
runs, a downconverter in the antenna. I don't know how to tell the
difference from part number, but I know the truetimes my employer uses
all have the downconverter option and the option is very common.
Tim N3QE
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[Michael Perrett]

Since your antennas have a lot of gain I assume they are active and require
a DC voltage to the LNA. Does the XL-DC provide that voltage (sometime you
have to select active or passive antenna)?
Michael / K7HIL

Post by Doug Ronald
I'm hoping someone can shed some light on my problem receiving any GPS satellites.
I have two TrueTime GPS Time & Frequency Receivers, Model XL-DC. One has a
regular crystal oscillator, and the other one has a rubidium oscillator. I
have two outdoor GPS antennas with internal LNAs, one a 28 dB gain unit,
and the other a 40 dB unit. When either antenna is connected to my Lucent
KS-24361, it locks right up and tracks up to 8 satellites. When either of
"Looking for GPS satellites".
In the Alarm menu of either XL-DC there is an alarm for Antenna. Both
units say "OK" and if I disconnect the antenna they both logically say
"Open". So, what is the problem? I can't believe I don't have enough
signal, after the Lucent locks-up right away. Is it possible the TrueTime
sanctioned antenna has a down converter in it, perhaps placing the GPS
signal from L-band to some lower frequency? I would appreciate any info the
group might have...
-Doug Ronald
W6DSR
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[Azelio Boriani]

Yes, the TrueTime unit needs its antenna/downconverter to work. Other
GPSDOs, like the Meinberg units GPS-SA used in the Rohde Schwarz
ED167MP have this arrangement.

Post by Doug Ronald
I'm hoping someone can shed some light on my problem receiving any GPS satellites.
I have two TrueTime GPS Time & Frequency Receivers, Model XL-DC. One has a regular crystal oscillator, and the other one has a rubidium oscillator. I have two outdoor GPS antennas with internal LNAs, one a 28 dB gain unit, and the other a 40 dB unit. When either antenna is connected to my Lucent KS-24361, it locks right up and tracks up to 8 satellites. When either of the antennas is connected to the XL-DCs, they just sit there and status : "Looking for GPS satellites".
In the Alarm menu of either XL-DC there is an alarm for Antenna. Both units say "OK" and if I disconnect the antenna they both logically say "Open". So, what is the problem? I can't believe I don't have enough signal, after the Lucent locks-up right away. Is it possible the TrueTime sanctioned antenna has a down converter in it, perhaps placing the GPS signal from L-band to some lower frequency? I would appreciate any info the group might have...
-Doug Ronald
W6DSR
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[Mike Cook]

The XL-DC Can use either a normal L1 or Down converter Antenna according to the manual. <http://www.prostudioconnection.net/1112/xl-dc-manual.pdf>

If your antenna works with the Lucent then it will be a normal one. Does your XL-DC have any option codes?


"Ceux qui sont prêts à abandonner une liberté essentielle pour obtenir une petite et provisoire sécurité, ne méritent ni liberté ni sécurité."
Benjimin Franklin

Post by Doug Ronald
I'm hoping someone can shed some light on my problem receiving any GPS satellites.
I have two TrueTime GPS Time & Frequency Receivers, Model XL-DC. One has a regular crystal oscillator, and the other one has a rubidium oscillator. I have two outdoor GPS antennas with internal LNAs, one a 28 dB gain unit, and the other a 40 dB unit. When either antenna is connected to my Lucent KS-24361, it locks right up and tracks up to 8 satellites. When either of the antennas is connected to the XL-DCs, they just sit there and status : "Looking for GPS satellites".
In the Alarm menu of either XL-DC there is an alarm for Antenna. Both units say "OK" and if I disconnect the antenna they both logically say "Open". So, what is the problem? I can't believe I don't have enough signal, after the Lucent locks-up right away. Is it possible the TrueTime sanctioned antenna has a down converter in it, perhaps placing the GPS signal from L-band to some lower frequency? I would appreciate any info the group might have...
-Doug Ronald
W6DSR
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[Doug Ronald]

I want to thank everyone who jumped in to contribute on my issue, especially Mike who supplied a much needed manual for this instrument.

Well, one unit with the xtal oscillator, had the upconverter end of the downconverter/upconverter chain in the chassis which was easily bypassed. Once that was accomplished, it locked up fairly quickly, however the LCD display had many bad segments. The rubidium unit has a defective Trimble receiver as it never gets out of the "looking for satellites" mode even after hours of on time, but it has a pristine LCD display, so I swapped around parts, and now have a good working standard. The xtal unit draws about half the power that the rubidium unit draws, so that one shall be my standard since it's on 24/7.

It was rewarding to use the TrueTime 10 MHz output for the reference input to my HP-5370B, and the frequency input of the counter connected to the Lucent 15 MHz standard. Both standards are completely independent right up to the antennas, and the counter shows only a few milliHertz variation.

Thanks again,
-Doug, W6DSR

-----Original Message-----
From: time-nuts [mailto:time-nuts-***@febo.com] On Behalf Of Mike Cook
Sent: Thursday, February 26, 2015 4:13 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] No GPS satellites
Importance: Low

The XL-DC Can use either a normal L1 or Down converter Antenna according to the manual. <http://www.prostudioconnection.net/1112/xl-dc-manual.pdf>

If your antenna works with the Lucent then it will be a normal one. Does your XL-DC have any option codes?


"Ceux qui sont prêts à abandonner une liberté essentielle pour obtenir une petite et provisoire sécurité, ne méritent ni liberté ni sécurité."
Benjimin Franklin

Post by Doug Ronald
I'm hoping someone can shed some light on my problem receiving any GPS satellites.
I have two TrueTime GPS Time & Frequency Receivers, Model XL-DC. One has a regular crystal oscillator, and the other one has a rubidium oscillator. I have two outdoor GPS antennas with internal LNAs, one a 28 dB gain unit, and the other a 40 dB unit. When either antenna is connected to my Lucent KS-24361, it locks right up and tracks up to 8 satellites. When either of the antennas is connected to the XL-DCs, they just sit there and status : "Looking for GPS satellites".
In the Alarm menu of either XL-DC there is an alarm for Antenna. Both units say "OK" and if I disconnect the antenna they both logically say "Open". So, what is the problem? I can't believe I don't have enough signal, after the Lucent locks-up right away. Is it possible the TrueTime sanctioned antenna has a down converter in it, perhaps placing the GPS signal from L-band to some lower frequency? I would appreciate any info the group might have...
-Doug Ronald
W6DSR
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[Mike Cook]

Just a heads up as I stumbled on an interesting XL-DC plugin module for sale on ebay while looking for info for Doug.
TrueTime Symmetricom XL-DC FTM-III AC Line Frequency Measurement & Time Monitor

Unfortunately I don’t have an XL-DC, but it looks just just the tick for a time nut who has.


"Ceux qui sont prêts à abandonner une liberté essentielle pour obtenir une petite et provisoire sécurité, ne méritent ni liberté ni sécurité."
Benjimin Franklin

Post by Doug Ronald
I'm hoping someone can shed some light on my problem receiving any GPS satellites.
I have two TrueTime GPS Time & Frequency Receivers, Model XL-DC. One has a regular crystal oscillator, and the other one has a rubidium oscillator. I have two outdoor GPS antennas with internal LNAs, one a 28 dB gain unit, and the other a 40 dB unit. When either antenna is connected to my Lucent KS-24361, it locks right up and tracks up to 8 satellites. When either of the antennas is connected to the XL-DCs, they just sit there and status : "Looking for GPS satellites".
In the Alarm menu of either XL-DC there is an alarm for Antenna. Both units say "OK" and if I disconnect the antenna they both logically say "Open". So, what is the problem? I can't believe I don't have enough signal, after the Lucent locks-up right away. Is it possible the TrueTime sanctioned antenna has a down converter in it, perhaps placing the GPS signal from L-band to some lower frequency? I would appreciate any info the group might have...
-Doug Ronald
W6DSR
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[Tom Van Baak]

Mike,

That's the same card I used for the 40-day run:
http://leapsecond.com/pages/mains/

It's robust and professional (used in the electric grid industry) and nice if you already have a working XL-DC but most of us now use a $1 microcontroller or DCD pin and NTP to track mains phase & frequency.

/tvb

Post by Mike Cook
Just a heads up as I stumbled on an interesting XL-DC plugin module for sale on ebay while looking for info for Doug.
TrueTime Symmetricom XL-DC FTM-III AC Line Frequency Measurement & Time Monitor
Unfortunately I don’t have an XL-DC, but it looks just just the tick for a time nut who has.
"Ceux qui sont prêts à abandonner une liberté essentielle pour obtenir une petite et provisoire sécurité, ne méritent ni liberté ni sécurité."
Benjimin Franklin

Post by Doug Ronald
I'm hoping someone can shed some light on my problem receiving any GPS satellites.
I have two TrueTime GPS Time & Frequency Receivers, Model XL-DC. One has a regular crystal oscillator, and the other one has a rubidium oscillator. I have two outdoor GPS antennas with internal LNAs, one a 28 dB gain unit, and the other a 40 dB unit. When either antenna is connected to my Lucent KS-24361, it locks right up and tracks up to 8 satellites. When either of the antennas is connected to the XL-DCs, they just sit there and status : "Looking for GPS satellites".
In the Alarm menu of either XL-DC there is an alarm for Antenna. Both units say "OK" and if I disconnect the antenna they both logically say "Open". So, what is the problem? I can't believe I don't have enough signal, after the Lucent locks-up right away. Is it possible the TrueTime sanctioned antenna has a down converter in it, perhaps placing the GPS signal from L-band to some lower frequency? I would appreciate any info the group might have...
-Doug Ronald
W6DSR
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[Ben Hall]

Hi Tom and list,

I joined the list a few days ago after getting my HP Z3801 back running
after a couple of years of it being off-line. I'm using it as a 10 MHz
frequency standard for my various ham-radio activities.

...but most of us now use a $1
microcontroller or DCD pin and NTP to track mains phase & frequency.

I'm going to have to build one of these. Assume you have some sort of
circuit that converts low-voltage AC from a transformer secondary to a
pulse train, start a timer, and count x amount of pulses?

Very interesting.

thanks much,
ben
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[Charles Steinmetz]

Post by Ben Hall
I'm going to have to build one of these. Assume you have some sort
of circuit that converts low-voltage AC from a transformer secondary
to a pulse train, start a timer, and count x amount of pulses?

Here is a zero-cross detector designed for this purpose:

<http://www.ko4bb.com/manuals/download.php?file=02_GPS_Timing/Simple_AC_Mains_Zero_Crossing_Detector.pdf>

Most mains-nuts feed the ZCD pulse to the DCD line of a PC's RS232
port and use the computer to time-stamp the crossings and append them
to a file of such time stamps.

Alternatively, Tom designed the picPET Precision Event Timer to do
this sort of timestamping:

<http://www.leapsecond.com/pic/picpet.htm>

An Ardu/berry/bone with a flash card can also be used, so you don't
need to leave a PC running.

Best regards,

Charles



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[Philip Gladstone]

Post by Charles Steinmetz

I'm going to have to build one of these. Assume you have some sort of
circuit that converts low-voltage AC from a transformer secondary to
a pulse train, start a timer, and count x amount of pulses?

<http://www.ko4bb.com/manuals/download.php?file=02_GPS_Timing/Simple_AC_Mains_Zero_Crossing_Detector.pdf>
Most mains-nuts feed the ZCD pulse to the DCD line of a PC's RS232
port and use the computer to time-stamp the crossings and append them
to a file of such time stamps.

If we all did this, then I realize that we could identify the different
power grids. However, I wonder if there is any interesting variation
*within* a grid. As the electricity flows vary throughout the day, it
seems possible that the phase difference between two people on the same
grid would actually change (a bit).

Has anybody done this experiment?

Philip
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[Bob Camp]

HI

Post by Charles Steinmetz

I'm going to have to build one of these. Assume you have some sort of
circuit that converts low-voltage AC from a transformer secondary to
a pulse train, start a timer, and count x amount of pulses?

<http://www.ko4bb.com/manuals/download.php?file=02_GPS_Timing/Simple_AC_Mains_Zero_Crossing_Detector.pdf>
Most mains-nuts feed the ZCD pulse to the DCD line of a PC's RS232
port and use the computer to time-stamp the crossings and append them
to a file of such time stamps.

If we all did this, then I realize that we could identify the different power grids. However, I wonder if there is any interesting variation *within* a grid. As the electricity flows vary throughout the day, it seems possible that the phase difference between two people on the same grid would actually change (a bit).
Has anybody done this experiment?

It’s done by utilities to monitor power flow and balance electric grids. The first data on this (grid vs GPS) date to the 1980’s. I think the
paper I recall was done by Quebec Hydro. Since then it’s become a pretty standard monitoring tool.

Bob

Philip
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[Magnus Danielson]

Hi Bob,

Post by Bob Camp
HI

Post by Charles Steinmetz

I'm going to have to build one of these. Assume you have some sort of
circuit that converts low-voltage AC from a transformer secondary to
a pulse train, start a timer, and count x amount of pulses?

<http://www.ko4bb.com/manuals/download.php?file=02_GPS_Timing/Simple_AC_Mains_Zero_Crossing_Detector.pdf>
Most mains-nuts feed the ZCD pulse to the DCD line of a PC's RS232
port and use the computer to time-stamp the crossings and append them
to a file of such time stamps.

If we all did this, then I realize that we could identify the different power grids. However, I wonder if there is any interesting variation *within* a grid. As the electricity flows vary throughout the day, it seems possible that the phase difference between two people on the same grid would actually change (a bit).
Has anybody done this experiment?

It’s done by utilities to monitor power flow and balance electric grids. The first data on this (grid vs GPS) date to the 1980’s. I think the
paper I recall was done by Quebec Hydro. Since then it’s become a pretty standard monitoring tool.

Yes. They implemented the first Phasor-Measurement Unit (PMU), it went
into the IEEE 1344 standard, but had many issues with it and created a
new standard in IEEE C37.118, which has since been split into IEEE
C37.118.1 and C37.118.2 with the advent of the IEC 61850 context, where
the data-transport is being replaced, but the measurement methods is
maintained in C37.118.1.

For an intro, you can read this paper:
http://rubidium.dyndns.org/~magnus/papers/KTH_paper1.pdf

Cheers,
Magnus
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[Tom Van Baak]

Post by Philip Gladstone
If we all did this, then I realize that we could identify the different
power grids. However, I wonder if there is any interesting variation
*within* a grid. As the electricity flows vary throughout the day, it
seems possible that the phase difference between two people on the same
grid would actually change (a bit).
Has anybody done this experiment?
Philip

Yes, it's really quite interesting and very easy to do. Check the time nuts archives -- over the years there are by now hundreds of postings about measuring mains phase and frequency. See also:

http://leapsecond.com/pages/mains/
Loading Image...
http://leapsecond.com/pages/ac-detect/

There are many wonderful web sites that deal with power line frequency; some with live plots. Just google for words like: mains frequency detect accuracy stability measurement

Also, make sure to read the growing literature about ENF:
http://en.wikipedia.org/wiki/Electrical_network_frequency_analysis

/tvb
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[Ben Hall]

Post by Tom Van Baak
There are many wonderful web sites that deal with power line
frequency; some with live plots. Just google for words like: mains
frequency detect accuracy stability measurement

Been doing just that - fascinating! I'm getting closer to doing some
frequency / phase monitoring here.

From: <http://leapsecond.com/pages/mains-cv/>

"A convenient way to monitor power line phase or frequency is to
timestamp every cycle. This generates a lot of data...so for most
purposes we keep just one timestamp per second. This gives about 86400
samples per day."

Using a zero-crossing detector with the picPET and logging the timing of
each zero-crossing, how do you toss out the other 59 samples each second?

Doing this after-the-fact seems do-able with some software. I seem to
recall doing something like this with FORTRAN or BASIC. (open log file,
open output file, read log file line by line, tossing out 59 samples and
writing the 60th to the output file, reach EOF, close both log and
output file)

But...is there a clever way to do it up front? Time to do more reading.
I've seen some folks doing frequency / phase monitoring using an
Arduino, but nothing (yet) that uses a high-precision reference such as
10 MHz from a GPSDO.

On a side note...the Z3801 got a new outdoor GPS antenna yesterday.
Very happy with how well it is working:

<http://www.kd5byb.net/kd5bybgpscon/gpsstat.htm>

thanks much and 73,
ben, kd5byb
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[Ben Hall]

Post by Ben Hall
Using a zero-crossing detector with the picPET and logging the timing of
each zero-crossing, how do you toss out the other 59 samples each second?

I think I figured out a very obvious way.

~60 Hz AC --> zero crossing detector --> divide by 64 ripple counter

THEN feed the output of the div by 64 counter into picPET. It is
logging a little less than once a minute...but 60 vs 64...

thanks much and 73,
ben, kd5byb

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[Tom Van Baak]

Post by Ben Hall
I'm going to have to build one of these. Assume you have some sort of
circuit that converts low-voltage AC from a transformer secondary to a
pulse train, start a timer, and count x amount of pulses?

Hi Ben,

Any microcontroller will allow you to poll for or capture events. Many even have capture/timer capability in h/w. Using a continuously running multi-byte timer you just subtract the current time from the previous time to get time interval (period). The traditional method of starting or resetting a timer after each event is prone to accumulated timing errors. Making periodic snapshots of a continuous timer avoids this.

Note that timer wrap-around is transparent for binary counters, as long as your timer won't wrap twice between events. For example, a 16-bit 1 MHz timer is more than sufficient for measuring 60 Hz events (since 16667 < 65536) with 1 us resolution.

In pseudo-code:

event()
time_now = get_timer()
interval = time_now - time_then
time_then = time_now
serial_output(interval)

Now, there are subtle issues with how interrupts and timers work, depending on the microcontroller, but the basic idea of measuring the precise interval between moderately rapid events (like 50/60 Hz cycles) is simple.

/tvb
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[Tom Van Baak]

Post by Ben Hall
Using a zero-crossing detector with the picPET and logging the timing of
each zero-crossing, how do you toss out the other 59 samples each second?

Hi Ben,

1) The PC program that reads the serial port can toss lines it doesn't want.

2) Or you can prune the log file with a C program like this:

// filter to pass one of every N input lines
#include <stdio.h>
#include <stdlib.h>
int main (int argc, char *argv[])
{
long count = 0;
char line[1000];
long nth = (argc > 1) ? atol(argv[1]) : 60;
while (fgets(line, sizeof line, stdin) != NULL) {
if ((count++ % nth) == 0)
fputs(line, stdout);
}
return 0;
}

3) The other solution that I often use is a version of the picPET (pP19) that deliberately takes 990 ms to output the timestamp (events are counted in h/w). That way it still counts all cycles but only outputs one timestamp per second. This is sort of like putting a prescaler in front of the picPET, but better. Better because no h/w is needed and because it is more immune to false triggers than a pre-scaler. It also works without changes for both 50 Hz or 60 Hz grids.

Post by Ben Hall
Doing this after-the-fact seems do-able with some software. I seem to
recall doing something like this with FORTRAN or BASIC. (open log file,
open output file, read log file line by line, tossing out 59 samples and
writing the 60th to the output file, reach EOF, close both log and
output file)

Yes, see code above. Same logic in any language, but probably one line of code in awk or perl or python.

Post by Ben Hall
But...is there a clever way to do it up front? Time to do more reading.
I've seen some folks doing frequency / phase monitoring using an
Arduino, but nothing (yet) that uses a high-precision reference such as
10 MHz from a GPSDO.

If you do it up-front, like a pre-scaler, you have to worry about signal quality to avoid off-by-one glitches. You'll get lots of suggestions here on the mailing list and on the web about how to best detect zero-crossings. The circuits get pretty complex. It may surprise you that I don't do any of that.

The beauty of timestamping (instead of traditional counting) is that signal conditioning is much less important. I put raw 5 VAC into the PIC pin via a 10k resistor. That's it. Any "conditioning" can be done in software. About once a month I see a stray timestamp or an extra pulse. You just delete it. So you can recover from glitches. With counters you can't - which is why signal conditioning is critical in those designs.

/tvb
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[Ben Hall]

Hi Tom and list!

Thank you for the responses. This has been very educational.

Post by Tom Van Baak
1) The PC program that reads the serial port can toss lines it
doesn't want.

I'll publicly expose my silliness here - I never thought about the
program end of things. I was simply thinking something like an old
terminal program with logging turned on.

Last night in a sleepless moment I got to thinking: this seems like a
great use of a Raspberry Pi. It can parse the serial, save the data to
a file, start a new file each day, each week, etc... Plus, I can set it
up to be a network file location so I can analyze the files elsewhere
easily. I'm going to pursue this. I've got two already - one is a
GPS-based NTP server...the other is an ADS-B receiver / reporter.

Post by Tom Van Baak
3) The other solution that I often use is a version of the picPET
(pP19) that deliberately takes 990 ms to output the timestamp (events
are counted in h/w).

This would be perfect. While discarding the unwanted data should not be
hard...not having to do it at all is easier. ;)

Post by Tom Van Baak
Yes, see code above. Same logic in any language, but probably one
line of code in awk or perl or python.

I'll probably end up learning some python in doing the serial logger
above. It seems to be a language of choice for the Pi.

Post by Tom Van Baak
If you do it up-front, like a pre-scaler, you have to worry about
signal quality to avoid off-by-one glitches. You'll get lots of
suggestions here on the mailing list and on the web about how to best
detect zero-crossings. The circuits get pretty complex. It may
surprise you that I don't do any of that.

I wasn't aware of this, so its very good to know. :)

Post by Tom Van Baak
The beauty of timestamping (instead of traditional counting) is that
signal conditioning is much less important. I put raw 5 VAC into the
PIC pin via a 10k resistor. That's it. Any "conditioning" can be done
in software.

It is a lot simpler too. Simple is always good in my book. (mostly
because I'm too stupid to do much that is complex!)

thanks much and 73,
ben, kd5byb
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[DaveH]

Like this?

http://fnetpublic.utk.edu/gradientmap.html

I am the dot just below the Canadian border in WA State.

Dave

Post by Bill Hawkins
-----Original Message-----
Of Philip Gladstone
Sent: Friday, February 27, 2015 07:47
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Recording mains frequency/phase
[WAS: No GPSsatellites]

Post by Charles Steinmetz

I'm going to have to build one of these. Assume you have

some sort of

Post by Charles Steinmetz

circuit that converts low-voltage AC from a transformer

secondary to

Post by Charles Steinmetz

a pulse train, start a timer, and count x amount of pulses?

<http://www.ko4bb.com/manuals/download.php?file=02_GPS_Timing/
Simple_AC_Mains_Zero_Crossing_Detector.pdf>

Post by Charles Steinmetz
Most mains-nuts feed the ZCD pulse to the DCD line of a PC's RS232
port and use the computer to time-stamp the crossings and

append them

Post by Charles Steinmetz
to a file of such time stamps.

If we all did this, then I realize that we could identify the
different
power grids. However, I wonder if there is any interesting variation
*within* a grid. As the electricity flows vary throughout the day, it
seems possible that the phase difference between two people
on the same
grid would actually change (a bit).
Has anybody done this experiment?
Philip
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[Graham]

Dave,

That's cool. I am the dot just above the US / Canada border and just
below the Ontario/Quebec border in Eastern Ontario.

There are many (many) documents that can found using Google on the
subject of power grids and frequency and monitoring. I have only been
able to read through only a small handful. An interesting application of
time and frequency measurement.

cheers, Graham ve3gtc

Post by DaveH
Like this?
http://fnetpublic.utk.edu/gradientmap.html
I am the dot just below the Canadian border in WA State.
Dave

Post by Bill Hawkins
-----Original Message-----
Of Philip Gladstone
Sent: Friday, February 27, 2015 07:47
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Recording mains frequency/phase
[WAS: No GPSsatellites]

Post by Charles Steinmetz

I'm going to have to build one of these. Assume you have

some sort of

Post by Charles Steinmetz

circuit that converts low-voltage AC from a transformer

secondary to

Post by Charles Steinmetz

a pulse train, start a timer, and count x amount of pulses?

<http://www.ko4bb.com/manuals/download.php?file=02_GPS_Timing/
Simple_AC_Mains_Zero_Crossing_Detector.pdf>

Post by Charles Steinmetz
Most mains-nuts feed the ZCD pulse to the DCD line of a PC's RS232
port and use the computer to time-stamp the crossings and

append them

Post by Charles Steinmetz
to a file of such time stamps.

If we all did this, then I realize that we could identify the
different
power grids. However, I wonder if there is any interesting variation
*within* a grid. As the electricity flows vary throughout the day, it
seems possible that the phase difference between two people
on the same
grid would actually change (a bit).
Has anybody done this experiment?
Philip
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[Mark Sims]

Yes, it has been done... and it has some very interesting real world uses:
http://www.theregister.co.uk/2014/07/03/tinfoil_hatters_spook_says_nsa_can_track_whistleblowers_through_power_lines/

-----------------
If we all did this, then I realize that we could identify the different power grids. However, I wonder if there is any interesting variation *within* a grid. As the electricity flows vary throughout the day, it seems possible that the phase difference between two people on the same
grid would actually change (a bit).

Has anybody done this experiment?
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[Daniel Mendes]

I´m planning an experiment like that... I designed a board with an OCXO,
pic microcontroller, power supply, mains interface with optocoupler, and
SD card for data collection.. I plan to sincronize a counter running at
10MHz between them and log events at 5 different points in my city. The
boards also have a small Li-Ion battery and battery charger for short
power outages. Boards are manufatured and the most expensive items have
been bought, but not everything yet.

Daniel

Post by Mark Sims
http://www.theregister.co.uk/2014/07/03/tinfoil_hatters_spook_says_nsa_can_track_whistleblowers_through_power_lines/
-----------------
If we all did this, then I realize that we could identify the different power grids. However, I wonder if there is any interesting variation *within* a grid. As the electricity flows vary throughout the day, it seems possible that the phase difference between two people on the same
grid would actually change (a bit).
Has anybody done this experiment?
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[Charles Steinmetz]

I designed a board with an OCXO, pic microcontroller, power supply,
mains interface with optocoupler, and SD card for data
collection.. * * * The boards also have a small Li-Ion
battery and battery charger for short power outages. Boards are
manufatured and the most expensive items have been bought, but not
everything yet.

I'm not a grid-nut myself, but your project sounds very
interesting. I designed the "simple zero-cross detector" because it
appeared to me that many potential grid-nuts may be put off by the
need to design and construct data collection tools, and I thought
that a very simple hardware detector running into an RS232 port might
lower this barrier enough to allow more prospective grid-nuts to
play. But there is still the matter of receiving, formatting, and
storing the raw data, and the need to leave a computer on 24/7. Your
hardware solves these issues.

Can you share the construction details (schematics, firmware, board files)?

Do you plan to make boards or kits available?

Also, you say you plan to "synchronize a counter between them." How
do you plan to do that without some sort of common-view timing source
at each site (GPS, NTP, etc.), or do you plan to have common-view timing?

Very interesting project -- congratulations, and please keep us updated.

Best regards,

Charles


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[Tom Van Baak]

Hi Daniel,

That will be an interesting experiment. I'm happy you are doing it. You may want to run all five boards within the same house first -- to establish your noise floor and to check your post-processing (non-aligned log files, glitches, power fails, oscillator drift, etc.).

Here's one from a couple years ago, between two cities, and two states.
http://leapsecond.com/pages/mains-cv/

/tvb

----- Original Message -----
From: "Daniel Mendes" <***@gmail.com>
To: "Discussion of precise time and frequency measurement" <time-***@febo.com>
Sent: Saturday, February 28, 2015 10:34 AM
Subject: Re: [time-nuts] Recording mains frequency/phase [WAS: No GPSsatellites]



I´m planning an experiment like that... I designed a board with an OCXO,
pic microcontroller, power supply, mains interface with optocoupler, and
SD card for data collection.. I plan to sincronize a counter running at
10MHz between them and log events at 5 different points in my city. The
boards also have a small Li-Ion battery and battery charger for short
power outages. Boards are manufatured and the most expensive items have
been bought, but not everything yet.

Daniel

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[Daniel Mendes]

Post by Tom Van Baak
Hi Daniel,
That will be an interesting experiment. I'm happy you are doing it. You may want to run all five boards within the same house first -- to establish your noise floor and to check your post-processing (non-aligned log files, glitches, power fails, oscillator drift, etc.).

Surelly... I must first discover how well (or how badly) it works....

Post by Tom Van Baak
Here's one from a couple years ago, between two cities, and two states.
http://leapsecond.com/pages/mains-cv/

Thanks for the link!

Daniel

Post by Tom Van Baak
/tvb
----- Original Message -----
Sent: Saturday, February 28, 2015 10:34 AM
Subject: Re: [time-nuts] Recording mains frequency/phase [WAS: No GPSsatellites]
I´m planning an experiment like that... I designed a board with an OCXO,
pic microcontroller, power supply, mains interface with optocoupler, and
SD card for data collection.. I plan to sincronize a counter running at
10MHz between them and log events at 5 different points in my city. The
boards also have a small Li-Ion battery and battery charger for short
power outages. Boards are manufatured and the most expensive items have
been bought, but not everything yet.
Daniel
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[Mark Sims]

When I first came across that article on theregister.com, I thought that it was a rather cute idea and decided to give it a try. I set up a couple of data recorders that logged AC zero crossings to an SD card (with 64 Mhz clock resolution). They were set up around 8 miles apart. I also recorded a sound file at each location from a sound card (92 kHz sample rate). None of the recordings were time-synced and the recording time-bases were simple crystal oscillators. I cut a random sections out of the sound recordings and fed them into what amounts to a correlator program and ran it against the zero-crossing logs. It had very few problems finding a best-fit of the sound snippets to the appropriate zero crossing data files.
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[Daniel Mendes]

I designed a board with an OCXO, pic microcontroller, power supply,
mains interface with optocoupler, and SD card for data
collection.. * * * The boards also have a small Li-Ion
battery and battery charger for short power outages. Boards are
manufatured and the most expensive items have been bought, but not
everything yet.

I'm not a grid-nut myself, but your project sounds very interesting.
I designed the "simple zero-cross detector" because it appeared to me
that many potential grid-nuts may be put off by the need to design and
construct data collection tools, and I thought that a very simple
hardware detector running into an RS232 port might lower this barrier
enough to allow more prospective grid-nuts to play. But there is
still the matter of receiving, formatting, and storing the raw data,
and the need to leave a computer on 24/7. Your hardware solves these
issues.

Yes... Even at my house it would be cumbersome to let something so big
turned on 24/7 (small child, wife....). Ask for others to do it just
wouldn´t work, so I designed something that fitted into a small box.

Can you share the construction details (schematics, firmware, board
files)?

It´s not assembled yet. Still need to buy about half the components (but
the most expensive ones are already in hand). I´m sending the schematics
attached (no more... to big for the list... sent directly). When it´s
assembled and running i´ll post all the info somewere freelly avaiable
(i´m trying to start a blog with all the crazy junk I make...).

Do you plan to make boards or kits available?

No... but I have spare boards I can send away for free if someone wants
them. I just need to discover how to send them from Brazil overseas..
but it can´t be hard.

Also, you say you plan to "synchronize a counter between them." How do
you plan to do that without some sort of common-view timing source at
each site (GPS, NTP, etc.), or do you plan to have common-view timing?

I plan to sincronize once (when they are powered on and near each
other). They will be calibrated as well as I can (I have two 12 digits
frequencimeters). After that they can drift away, but I expect that the
OCXOs will make that negligible....

Very interesting project -- congratulations, and please keep us updated.

Thanks!

Daniel



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[Bill Hawkins]

Just a thought about interpreting data:

The mains frequency changes as the loads on the system change.
Dispatchers bring more generators on line or drop them.
Some of this is predictable, depending on business hours, weekends,
holidays and the seasons.

Just as one can take the crystal aging out of the frequency vs. time
display, it should be possible to subtract an average of the variations
caused by predictable load changes. This leaves a display that makes
unusual deviations much more visible.

The line frequency is not like a disciplined crystal oscillator. There
is no phase locked loop adjusting the line frequency, just dispatchers
trying to produce the same number of cycles per day. The length of a day
is precisely known from national time standards.

Short term plots (e.g. daily and weekly) of line frequency should be
referenced to time of day, not elapsed time.

It would be interesting to see how the daily load averages vary from
region to region.

Bill Hawkins

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