vlf-disciplined OCXO circuit
Does anyone know of designs for disciplined OCXOs that are referenced to
off-air, especially VLF, signals other than GPS/GNSS please? With modules
for the latter being so cheap this might seem pointless but there are some
potential advantages.
- GPS reception at indoor locations where mechanical clocks need to be
monitored is often (usually?) unavailable because of shadowing and building
absorbtion and it's usually inconvenient to run a cable. - GPS is increasingly likely to be jammed either by criminal elements
or "state actors". - VLF (the likes of WWVB / MSF / DCF77 / e-Loran) is more likely to be
received indoors. - E-Loran is being tipped as an off-air time source to back up GPS and
will become increasingly available. - There's the possibility of a multi-standard receiver that might find
and lock to any available source, and potentially to several.
Obviously there are a lot of very cheap modules around to receive the
signals but these discard the carrier and just output the time-code logic
signal. I have seen a design for an MSF-locked standard in discrete
components and more recently an MSF receiver implemented as
direct-conversion SDR on a Raspberry Pi Pico which phase locks its internal
digital LO to the carrier but I suspect that its phase noise would be pretty
ropey - really intended as a time, not frequency, source.
- John Haine.
Hi
The most basic question here is “where do you want to do this?”
VLF (even Loran) is a limited range sort of thing. If you live in the US, your choices are different than
the UK. If you live in NZ, your choices are a bit limited … sorry about that …
Next layer once you have a site “in range”, just how far is that?
If you happen to be 10’s of miles from the site, you will not have much propagation to deal with.
It’s a lot more likely that you are hundreds (or maybe even thousands) of miles away. Miami to
WWVB is a bit over 2,000 miles.
Over a long path, you will indeed get into propagation effects. These can be pretty substantial.
Most of it is predictable, there will always be grubby side effects that come in at some level. If
you are after a “modern” sort of GPSDO performance, you will need to come up with a method
of dealing with those. Does this apply to you? Let’s assume it does and move on.
One traditional approach to dealing with this is to go to a Rb rather than an OCXO as the standard.
You then decide on a “safe” time range during the day. It might be the middle of the night. You
take your data then and shove it into the control function. Your correction process is a bit slow
as a result.
No this is not even close to a full list of what to dig into. There are already enough choices and
turns in the road that covering all the cases is heading into a lot of things that simply will not
matter.
Yes, we could dive into your “why” section. Needless to say, there is a lot of debate there and
a wide number of fixes for this or fixes for that. None of these systems by themselves are immune
to “issues”. There are alternatives past those on your list.
Fun !!!
Bob
On Sep 22, 2025, at 5:19 AM, john.haine--- via time-nuts time-nuts@lists.febo.com wrote:
Does anyone know of designs for disciplined OCXOs that are referenced to
off-air, especially VLF, signals other than GPS/GNSS please? With modules
for the latter being so cheap this might seem pointless but there are some
potential advantages.
- GPS reception at indoor locations where mechanical clocks need to be
monitored is often (usually?) unavailable because of shadowing and building
absorbtion and it's usually inconvenient to run a cable. - GPS is increasingly likely to be jammed either by criminal elements
or "state actors". - VLF (the likes of WWVB / MSF / DCF77 / e-Loran) is more likely to be
received indoors. - E-Loran is being tipped as an off-air time source to back up GPS and
will become increasingly available. - There's the possibility of a multi-standard receiver that might find
and lock to any available source, and potentially to several.
Obviously there are a lot of very cheap modules around to receive the
signals but these discard the carrier and just output the time-code logic
signal. I have seen a design for an MSF-locked standard in discrete
components and more recently an MSF receiver implemented as
direct-conversion SDR on a Raspberry Pi Pico which phase locks its internal
digital LO to the carrier but I suspect that its phase noise would be pretty
ropey - really intended as a time, not frequency, source.
- John Haine.
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
john.haine--- via time-nuts writes:
Does anyone know of designs for disciplined OCXOs that are referenced to
off-air, especially VLF, signals other than GPS/GNSS please?
I played a lot with that many years ago.
You can do a lot with a small microcontroller with an ADC which does
something like a million samples per second.
My favourite was this:
Run the ADC at 1 MHz from your reference clock, sum the samples into
a 1000 long circular buffer:
alpha = 1e-5; // play with this
n = 0
while (1) {
x = get_sample()
buffer[x] += (x - buffer[x]) * alpha
x +=1
if x == 1000:
x = 0;
}
This buffer now holds the output of a 1kHz combfilter over your input
signal, which means you can extract the phase and amplitude of any
signal on a multiple of 1kHz from that single buffer.
Simply multiply the 1000 samples in the buffer with sin() and cos()
of your desired frequency and calculate the magnitude and angle of
the resulting vector:
fx = 60 // 60 khz
ssin = 0.0
scos = 0.0
for i in range(1000):
ssin += sin(2 * PI * i / 1000 * buffer[i]
scos += sin(2 * PI * i / 1000 * buffer[i]
ampl = hypot(ssin, scos)
angle = atan2(ssin, scos)
Now do that for as many signals as you want, and steer your
reference clock accordingly.
If you want to also track signals on half kHz (like DCF77), make
the buffer 2000 samples.
One paticularly interesting case is using a buffer exactly one
second long (=1 million in this example), that would allow you
to extract both the phase and the modulation from signals
like DCF77 and WWVB
The Pi2 has a 500kS ADC and two CPU cores, so it is nearly perfect,
provided you can lock the frequency to your house standard - or
just use an external ADC, plenty of eval boards out there.
I didn't document very much of the fun I had, but there is
some stuff here:
https://phk.freebsd.dk/loran-c/CW/
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
I have a design for a WWVB Receiver, which is an SDR running on a 600 MHz
ARM M7. It phase locks the receiver to the incoming 60 kHz signal, by
steering an on-board TCVCXO. It extracts the AM modulation, phase
modulation, and only extracts carrier frequency during a known phase state
window. This constitutes a "sensor", which could then be used to steer a
separate secondary frequency/time standard.
After running it for a year, and taking some data, I would summarize that,
at any distance from the transmitter, the WWVB "sensor" is two or three
orders of magnitude less accurate than even the simplest GPS receiver
system.
The WWVB signal as transmitted is derived from time/frequency standards
that are derived from the same source as the GPS system. But the
propagation mechanism is much less stable.
So, many day averaging and some time windowing and gating, and ionosphere
disturbance intelligence are going to be required to extract something more
accurate from WWVB.
So, whether you are looking for time or frequency information, you will
need to decide just how much accuracy is important to you. If you are
monitoring some mechanical clocks, or looking for fractional milli-second
accuracy, it might be OK. If you are trying to provide a back-up for a GPS
system, beware.
I live in Austin Texas, which is about 900 miles from the WWVB transmitter.
The main night time propagation mode is that the signal is refracted by the
lower D layer, which appears to move up and down day to night, with
multipath, as well as appears to move up and down with solar flare activity
which can also charge the ionosphere.
Daytime propagation mode is mostly ground wave. (More loss, but more
stable.) And here in Austin we can get total cancellation (and half cycle
slips) of the received signal as the propagation mode changes between day
and night propagation modes
I typically find that the day to night path difference is on the order of
22 microseconds and a typical minor solar flare will create a few hours
long 5 or 6 microsecond time change. Bigger flares, bigger impact.
If you look at the VLF systems that Hewlett-Packard sold prior to GPS
availability, the OCXO secondary standard was not managed directly by the
VLF receiver. The receiver drove a paper chart recorder, and the lab
personnel were expected to examine the paper tape, at the same time every
afternoon (when the path was most stable and repeatable) and then use their
judgement to manually adjust the OCXO secondary standard to the 'correct'
frequency.
This is not a simple algorithm to convert to software.
The VLF signals do penetrate wooden buildings (homes) reasonably well. But
they are also subject to interference.
Any lightning activity within about 150 miles causes signal degradation and
signals become unusable when the lightning activity is within about 50
miles.
Here in the US, with power systems at 60 Hz, the harmonics from any
computer monitor screen refreshed at 60 Hz (or a multiple) can cause
interference to the WWVB receiver. So I find that the WWVB antenna should
not be within 15 to 20 feet of any computer monitor screen, which limits
antenna placement in the modern home or lab.
I have a friend who has one of my receivers, and is attempting to do
multiple day averaging to perhaps do very long term steering of a rubidium
secondary standard. Perhaps more to come on that topic, someday.
As Bob says, fun.
--- Graham
==
On Mon, Sep 22, 2025 at 1:02 PM Bob Camp via time-nuts <
time-nuts@lists.febo.com> wrote:
Hi
The most basic question here is “where do you want to do this?”
VLF (even Loran) is a limited range sort of thing. If you live in the US,
your choices are different than
the UK. If you live in NZ, your choices are a bit limited … sorry about
that …
Next layer once you have a site “in range”, just how far is that?
If you happen to be 10’s of miles from the site, you will not have much
propagation to deal with.
It’s a lot more likely that you are hundreds (or maybe even thousands) of
miles away. Miami to
WWVB is a bit over 2,000 miles.
Over a long path, you will indeed get into propagation effects. These can
be pretty substantial.
Most of it is predictable, there will always be grubby side effects that
come in at some level. If
you are after a “modern” sort of GPSDO performance, you will need to come
up with a method
of dealing with those. Does this apply to you? Let’s assume it does and
move on.
One traditional approach to dealing with this is to go to a Rb rather than
an OCXO as the standard.
You then decide on a “safe” time range during the day. It might be the
middle of the night. You
take your data then and shove it into the control function. Your
correction process is a bit slow
as a result.
No this is not even close to a full list of what to dig into. There are
already enough choices and
turns in the road that covering all the cases is heading into a lot of
things that simply will not
matter.
Yes, we could dive into your “why” section. Needless to say, there is a
lot of debate there and
a wide number of fixes for this or fixes for that. None of these systems
by themselves are immune
to “issues”. There are alternatives past those on your list.
Fun !!!
Bob
On Sep 22, 2025, at 5:19 AM, john.haine--- via time-nuts <
time-nuts@lists.febo.com> wrote:
Does anyone know of designs for disciplined OCXOs that are referenced to
off-air, especially VLF, signals other than GPS/GNSS please? With
modules
for the latter being so cheap this might seem pointless but there are
some
potential advantages.
-
GPS reception at indoor locations where mechanical clocks need to
be
monitored is often (usually?) unavailable because of shadowing and
building
absorbtion and it's usually inconvenient to run a cable.
-
GPS is increasingly likely to be jammed either by criminal elements
or "state actors".
-
VLF (the likes of WWVB / MSF / DCF77 / e-Loran) is more likely to
be
received indoors.
-
E-Loran is being tipped as an off-air time source to back up GPS
and
will become increasingly available.
-
There's the possibility of a multi-standard receiver that might
find
and lock to any available source, and potentially to several.
Obviously there are a lot of very cheap modules around to receive the
signals but these discard the carrier and just output the time-code logic
signal. I have seen a design for an MSF-locked standard in discrete
components and more recently an MSF receiver implemented as
direct-conversion SDR on a Raspberry Pi Pico which phase locks its
internal
digital LO to the carrier but I suspect that its phase noise would be
pretty
ropey - really intended as a time, not frequency, source.
-
John Haine.
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
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John,
Not a guru...but I would worry about the phase shift and potential reflection/refraction/noise effects of disciplining an oscillator to a far-away VLF carrier signal. Not sure what the relative accuracy might be...but it's probably quite a bit less than disciplining to GPS...and maybe even WWV. At the "right" times of day, WWV can get you to about 1-2 Hz @ 10 MHz. Wonder what VLF might be?
Interesting!
Regards,
Kirk, NT0ZRochester, MN
My book, "Stealth Amateur Radio," is now available from www.stealthamateur.com and on the Amazon Kindle (soon)
On Monday, September 22, 2025 at 10:01:45 AM CDT, john.haine--- via time-nuts <time-nuts@lists.febo.com> wrote:
Does anyone know of designs for disciplined OCXOs that are referenced to
off-air, especially VLF, signals other than GPS/GNSS please? With modules
for the latter being so cheap this might seem pointless but there are some
potential advantages.
* GPS reception at indoor locations where mechanical clocks need to be
monitored is often (usually?) unavailable because of shadowing and building
absorbtion and it's usually inconvenient to run a cable.
* GPS is increasingly likely to be jammed either by criminal elements
or "state actors".
* VLF (the likes of WWVB / MSF / DCF77 / e-Loran) is more likely to be
received indoors.
* E-Loran is being tipped as an off-air time source to back up GPS and
will become increasingly available.
* There's the possibility of a multi-standard receiver that might find
and lock to any available source, and potentially to several.
Obviously there are a lot of very cheap modules around to receive the
signals but these discard the carrier and just output the time-code logic
signal. I have seen a design for an MSF-locked standard in discrete
components and more recently an MSF receiver implemented as
direct-conversion SDR on a Raspberry Pi Pico which phase locks its internal
digital LO to the carrier but I suspect that its phase noise would be pretty
ropey - really intended as a time, not frequency, source.
* John Haine.
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
Hi Graham:
I'd add that some WWVB clocks go crazy if they are near Wi-Fi, which includes routers and cell phones.
https://prc68.com/I/Loop.shtml#RFI
--
Have Fun,
Brooke Clarke
https://www.PRC68.com
axioms:
- The extent to which you can fix or improve something will be limited by how well you understand how it works.
- Everybody, with no exceptions, holds false beliefs.
-------- Original Message --------
I have a design for a WWVB Receiver, which is an SDR running on a 600 MHz
ARM M7. It phase locks the receiver to the incoming 60 kHz signal, by
steering an on-board TCVCXO. It extracts the AM modulation, phase
modulation, and only extracts carrier frequency during a known phase state
window. This constitutes a "sensor", which could then be used to steer a
separate secondary frequency/time standard.
After running it for a year, and taking some data, I would summarize that,
at any distance from the transmitter, the WWVB "sensor" is two or three
orders of magnitude less accurate than even the simplest GPS receiver
system.
The WWVB signal as transmitted is derived from time/frequency standards
that are derived from the same source as the GPS system. But the
propagation mechanism is much less stable.
So, many day averaging and some time windowing and gating, and ionosphere
disturbance intelligence are going to be required to extract something more
accurate from WWVB.
So, whether you are looking for time or frequency information, you will
need to decide just how much accuracy is important to you. If you are
monitoring some mechanical clocks, or looking for fractional milli-second
accuracy, it might be OK. If you are trying to provide a back-up for a GPS
system, beware.
I live in Austin Texas, which is about 900 miles from the WWVB transmitter.
The main night time propagation mode is that the signal is refracted by the
lower D layer, which appears to move up and down day to night, with
multipath, as well as appears to move up and down with solar flare activity
which can also charge the ionosphere.
Daytime propagation mode is mostly ground wave. (More loss, but more
stable.) And here in Austin we can get total cancellation (and half cycle
slips) of the received signal as the propagation mode changes between day
and night propagation modes
I typically find that the day to night path difference is on the order of
22 microseconds and a typical minor solar flare will create a few hours
long 5 or 6 microsecond time change. Bigger flares, bigger impact.
If you look at the VLF systems that Hewlett-Packard sold prior to GPS
availability, the OCXO secondary standard was not managed directly by the
VLF receiver. The receiver drove a paper chart recorder, and the lab
personnel were expected to examine the paper tape, at the same time every
afternoon (when the path was most stable and repeatable) and then use their
judgement to manually adjust the OCXO secondary standard to the 'correct'
frequency.
This is not a simple algorithm to convert to software.
The VLF signals do penetrate wooden buildings (homes) reasonably well. But
they are also subject to interference.
Any lightning activity within about 150 miles causes signal degradation and
signals become unusable when the lightning activity is within about 50
miles.
Here in the US, with power systems at 60 Hz, the harmonics from any
computer monitor screen refreshed at 60 Hz (or a multiple) can cause
interference to the WWVB receiver. So I find that the WWVB antenna should
not be within 15 to 20 feet of any computer monitor screen, which limits
antenna placement in the modern home or lab.
I have a friend who has one of my receivers, and is attempting to do
multiple day averaging to perhaps do very long term steering of a rubidium
secondary standard. Perhaps more to come on that topic, someday.
As Bob says, fun.
--- Graham
==
On Mon, Sep 22, 2025 at 1:02 PM Bob Camp via time-nuts <
time-nuts@lists.febo.com> wrote:
Hi
The most basic question here is “where do you want to do this?”
VLF (even Loran) is a limited range sort of thing. If you live in the US,
your choices are different than
the UK. If you live in NZ, your choices are a bit limited … sorry about
that …
Next layer once you have a site “in range”, just how far is that?
If you happen to be 10’s of miles from the site, you will not have much
propagation to deal with.
It’s a lot more likely that you are hundreds (or maybe even thousands) of
miles away. Miami to
WWVB is a bit over 2,000 miles.
Over a long path, you will indeed get into propagation effects. These can
be pretty substantial.
Most of it is predictable, there will always be grubby side effects that
come in at some level. If
you are after a “modern” sort of GPSDO performance, you will need to come
up with a method
of dealing with those. Does this apply to you? Let’s assume it does and
move on.
One traditional approach to dealing with this is to go to a Rb rather than
an OCXO as the standard.
You then decide on a “safe” time range during the day. It might be the
middle of the night. You
take your data then and shove it into the control function. Your
correction process is a bit slow
as a result.
No this is not even close to a full list of what to dig into. There are
already enough choices and
turns in the road that covering all the cases is heading into a lot of
things that simply will not
matter.
Yes, we could dive into your “why” section. Needless to say, there is a
lot of debate there and
a wide number of fixes for this or fixes for that. None of these systems
by themselves are immune
to “issues”. There are alternatives past those on your list.
Fun !!!
Bob
On Sep 22, 2025, at 5:19 AM, john.haine--- via time-nuts <
time-nuts@lists.febo.com> wrote:
Does anyone know of designs for disciplined OCXOs that are referenced to
off-air, especially VLF, signals other than GPS/GNSS please? With
modules
for the latter being so cheap this might seem pointless but there are
some
potential advantages.
-
GPS reception at indoor locations where mechanical clocks need to
be
monitored is often (usually?) unavailable because of shadowing and
building
absorbtion and it's usually inconvenient to run a cable.
-
GPS is increasingly likely to be jammed either by criminal elements
or "state actors".
-
VLF (the likes of WWVB / MSF / DCF77 / e-Loran) is more likely to
be
received indoors.
-
E-Loran is being tipped as an off-air time source to back up GPS
and
will become increasingly available.
-
There's the possibility of a multi-standard receiver that might
find
and lock to any available source, and potentially to several.
Obviously there are a lot of very cheap modules around to receive the
signals but these discard the carrier and just output the time-code logic
signal. I have seen a design for an MSF-locked standard in discrete
components and more recently an MSF receiver implemented as
direct-conversion SDR on a Raspberry Pi Pico which phase locks its
internal
digital LO to the carrier but I suspect that its phase noise would be
pretty
ropey - really intended as a time, not frequency, source.
-
John Haine.
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
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I built a 162kHz reference based on the timing signal broadcasted by the Allouis station in France.
It is reliable, except every Tuesday mornings when it shuts down for maintenance !
Compared to GPS PPS I can reach about 10-11 ADEV in day time and 10-12 in a week.
Naturally impacted by perturbations on the path, day / night ionospheric disturbances and others.
But the other powerful commercial LF transmitters have now been shutdown (at least here in Europe)
Gilles.
Le 22 sept. 2025 à 21:13, Graham / KE9H via time-nuts time-nuts@lists.febo.com a écrit :
I have a design for a WWVB Receiver, which is an SDR running on a 600 MHz
ARM M7. It phase locks the receiver to the incoming 60 kHz signal, by
steering an on-board TCVCXO. It extracts the AM modulation, phase
modulation, and only extracts carrier frequency during a known phase state
window. This constitutes a "sensor", which could then be used to steer a
separate secondary frequency/time standard.
After running it for a year, and taking some data, I would summarize that,
at any distance from the transmitter, the WWVB "sensor" is two or three
orders of magnitude less accurate than even the simplest GPS receiver
system.
The WWVB signal as transmitted is derived from time/frequency standards
that are derived from the same source as the GPS system. But the
propagation mechanism is much less stable.
So, many day averaging and some time windowing and gating, and ionosphere
disturbance intelligence are going to be required to extract something more
accurate from WWVB.
So, whether you are looking for time or frequency information, you will
need to decide just how much accuracy is important to you. If you are
monitoring some mechanical clocks, or looking for fractional milli-second
accuracy, it might be OK. If you are trying to provide a back-up for a GPS
system, beware.
I live in Austin Texas, which is about 900 miles from the WWVB transmitter.
The main night time propagation mode is that the signal is refracted by the
lower D layer, which appears to move up and down day to night, with
multipath, as well as appears to move up and down with solar flare activity
which can also charge the ionosphere.
Daytime propagation mode is mostly ground wave. (More loss, but more
stable.) And here in Austin we can get total cancellation (and half cycle
slips) of the received signal as the propagation mode changes between day
and night propagation modes
I typically find that the day to night path difference is on the order of
22 microseconds and a typical minor solar flare will create a few hours
long 5 or 6 microsecond time change. Bigger flares, bigger impact.
If you look at the VLF systems that Hewlett-Packard sold prior to GPS
availability, the OCXO secondary standard was not managed directly by the
VLF receiver. The receiver drove a paper chart recorder, and the lab
personnel were expected to examine the paper tape, at the same time every
afternoon (when the path was most stable and repeatable) and then use their
judgement to manually adjust the OCXO secondary standard to the 'correct'
frequency.
This is not a simple algorithm to convert to software.
The VLF signals do penetrate wooden buildings (homes) reasonably well. But
they are also subject to interference.
Any lightning activity within about 150 miles causes signal degradation and
signals become unusable when the lightning activity is within about 50
miles.
Here in the US, with power systems at 60 Hz, the harmonics from any
computer monitor screen refreshed at 60 Hz (or a multiple) can cause
interference to the WWVB receiver. So I find that the WWVB antenna should
not be within 15 to 20 feet of any computer monitor screen, which limits
antenna placement in the modern home or lab.
I have a friend who has one of my receivers, and is attempting to do
multiple day averaging to perhaps do very long term steering of a rubidium
secondary standard. Perhaps more to come on that topic, someday.
As Bob says, fun.
--- Graham
==
On Mon, Sep 22, 2025 at 1:02 PM Bob Camp via time-nuts <
time-nuts@lists.febo.com> wrote:
Hi
The most basic question here is “where do you want to do this?”
VLF (even Loran) is a limited range sort of thing. If you live in the US,
your choices are different than
the UK. If you live in NZ, your choices are a bit limited … sorry about
that …
Next layer once you have a site “in range”, just how far is that?
If you happen to be 10’s of miles from the site, you will not have much
propagation to deal with.
It’s a lot more likely that you are hundreds (or maybe even thousands) of
miles away. Miami to
WWVB is a bit over 2,000 miles.
Over a long path, you will indeed get into propagation effects. These can
be pretty substantial.
Most of it is predictable, there will always be grubby side effects that
come in at some level. If
you are after a “modern” sort of GPSDO performance, you will need to come
up with a method
of dealing with those. Does this apply to you? Let’s assume it does and
move on.
One traditional approach to dealing with this is to go to a Rb rather than
an OCXO as the standard.
You then decide on a “safe” time range during the day. It might be the
middle of the night. You
take your data then and shove it into the control function. Your
correction process is a bit slow
as a result.
No this is not even close to a full list of what to dig into. There are
already enough choices and
turns in the road that covering all the cases is heading into a lot of
things that simply will not
matter.
Yes, we could dive into your “why” section. Needless to say, there is a
lot of debate there and
a wide number of fixes for this or fixes for that. None of these systems
by themselves are immune
to “issues”. There are alternatives past those on your list.
Fun !!!
Bob
On Sep 22, 2025, at 5:19 AM, john.haine--- via time-nuts <
time-nuts@lists.febo.com> wrote:
Does anyone know of designs for disciplined OCXOs that are referenced to
off-air, especially VLF, signals other than GPS/GNSS please? With
modules
for the latter being so cheap this might seem pointless but there are
some
potential advantages.
-
GPS reception at indoor locations where mechanical clocks need to
be
monitored is often (usually?) unavailable because of shadowing and
building
absorbtion and it's usually inconvenient to run a cable.
-
GPS is increasingly likely to be jammed either by criminal elements
or "state actors".
-
VLF (the likes of WWVB / MSF / DCF77 / e-Loran) is more likely to
be
received indoors.
-
E-Loran is being tipped as an off-air time source to back up GPS
and
will become increasingly available.
-
There's the possibility of a multi-standard receiver that might
find
and lock to any available source, and potentially to several.
Obviously there are a lot of very cheap modules around to receive the
signals but these discard the carrier and just output the time-code logic
signal. I have seen a design for an MSF-locked standard in discrete
components and more recently an MSF receiver implemented as
direct-conversion SDR on a Raspberry Pi Pico which phase locks its
internal
digital LO to the carrier but I suspect that its phase noise would be
pretty
ropey - really intended as a time, not frequency, source.
-
John Haine.
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Hi John,
These older for the 80s / 90s Spectracom Units did just what you are
looking for.
Unfortunately, they do not work anymore with WWVB as of the phase shift
modulation that was introduced in 2012
Working on a mod for to make them work now a days
here is a link to instruction manual for one of the 8164
https://manuals.repeater-builder.com/te-files/MISCELLANEOUS/Spectracom%208164%20Instruction.pdf
Best,
Mike Fowler
On Mon, Sep 22, 2025 at 10:01 AM john.haine--- via time-nuts <
time-nuts@lists.febo.com> wrote:
Does anyone know of designs for disciplined OCXOs that are referenced to
off-air, especially VLF, signals other than GPS/GNSS please? With modules
for the latter being so cheap this might seem pointless but there are some
potential advantages.
-
GPS reception at indoor locations where mechanical clocks need to
be
monitored is often (usually?) unavailable because of shadowing and building
absorbtion and it's usually inconvenient to run a cable.
-
GPS is increasingly likely to be jammed either by criminal elements
or "state actors".
-
VLF (the likes of WWVB / MSF / DCF77 / e-Loran) is more likely to
be
received indoors.
-
E-Loran is being tipped as an off-air time source to back up GPS
and
will become increasingly available.
-
There's the possibility of a multi-standard receiver that might
find
and lock to any available source, and potentially to several.
Obviously there are a lot of very cheap modules around to receive the
signals but these discard the carrier and just output the time-code logic
signal. I have seen a design for an MSF-locked standard in discrete
components and more recently an MSF receiver implemented as
direct-conversion SDR on a Raspberry Pi Pico which phase locks its internal
digital LO to the carrier but I suspect that its phase noise would be
pretty
ropey - really intended as a time, not frequency, source.
-
John Haine.
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
Hi,
I calculate the amplitude and phase of a sampled signal with the
goertzel algo https://en.wikipedia.org/wiki/Goertzel_algorithm.
It calculates the discrete fourier transform, i.e. amplitude and phase
for a single frequency at the cost of one multiply per sample.
No need to buffer samples.
const float fcc=2.0f*cosf(M_PI/16.0f); // signal freq / sample freq
= 1/32
fq2=0.0f;fq1=0.0f;
for(nn=0;nn<RECLEN;nn++){
while(1){ // wait for sample
if((ADC_ISR&(1<<2))>0){ // got it
dd=ADC_DR; // get sample
fq0=fq1*fcc-fq2+dd; // undamped second order recursive
filter
fq2=fq1;fq1=fq0;
break;
}
}
}
// unwrap result
double complex z =(float)(fq1-fq2cosf(M_PI/16))+ // Real part
I(float)(fq2*sinf(M_PI/16)); // imaginary part
Cheers
Detlef
Am 22.09.2025 um 19:12 schrieb Poul-Henning Kamp via time-nuts:
john.haine--- via time-nuts writes:
Does anyone know of designs for disciplined OCXOs that are referenced to
off-air, especially VLF, signals other than GPS/GNSS please?
I played a lot with that many years ago.
You can do a lot with a small microcontroller with an ADC which does
something like a million samples per second.
My favourite was this:
Run the ADC at 1 MHz from your reference clock, sum the samples into
a 1000 long circular buffer:
alpha = 1e-5; // play with this
n = 0
while (1) {
x = get_sample()
buffer[x] += (x - buffer[x]) * alpha
x +=1
if x == 1000:
x = 0;
}
This buffer now holds the output of a 1kHz combfilter over your input
signal, which means you can extract the phase and amplitude of any
signal on a multiple of 1kHz from that single buffer.
Simply multiply the 1000 samples in the buffer with sin() and cos()
of your desired frequency and calculate the magnitude and angle of
the resulting vector:
fx = 60 // 60 khz
ssin = 0.0
scos = 0.0
for i in range(1000):
ssin += sin(2 * PI * i / 1000 * buffer[i]
scos += sin(2 * PI * i / 1000 * buffer[i]
ampl = hypot(ssin, scos)
angle = atan2(ssin, scos)
Now do that for as many signals as you want, and steer your
reference clock accordingly.
If you want to also track signals on half kHz (like DCF77), make
the buffer 2000 samples.
One paticularly interesting case is using a buffer exactly one
second long (=1 million in this example), that would allow you
to extract both the phase and the modulation from signals
like DCF77 and WWVB
The Pi2 has a 500kS ADC and two CPU cores, so it is nearly perfect,
provided you can lock the frequency to your house standard - or
just use an external ADC, plenty of eval boards out there.
I didn't document very much of the fun I had, but there is
some stuff here:
https://phk.freebsd.dk/loran-c/CW/
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Anyone thought of, or implemented, a 50/60Hz VLF receiver?
Yes it would have horrible characteristics compared to a proper VLF
station, especially during power cuts. Personally I’m thinking more of
measuring the 50/60Hz “signal” than using it as a time source. And yes I’m
aware that it’s possible to do such measurements by plugging directly into
the grid, but I’d prefer not to do that for reasons.
I calculate the amplitude and phase of a sampled signal with the
goertzel algo https://en.wikipedia.org/wiki/Goertzel_algorithm.
The point about my suggestion, is that the per-sample math is very
trivial, and you can do the "heavy" math in the background at a
much lower rate and on multiple different carriers at the same time.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Hi
Back in the day a lot of us ran setups that locked to Loran or WWVB. Of the two, Loran seemed
to be the more common / more stable choice. We ran an Austron Loran device that did pretty well.
With WWVB, the answer was a strip chart recorder and working out what a wiggly line actually
was telling us.
Part of the “why” was our location. A master station for Loran was way closer than WWVB.
Since the master in a Loran chain transmits at much higher power than the other stations, that’s
the one you want to be near.
If we had been up in the northeastern US, WWVB happened to share 60KHz with other stations.
That tended to mess things up a bit. I’m glad we didn’t have to deal with that.
All of this was targeted at manually steering the house standard Rb to keep it on frequency. I was
amazed at just how little it drifted each month.
Bob
On Sep 23, 2025, at 11:51 AM, Michael Fowler via time-nuts time-nuts@lists.febo.com wrote:
Hi John,
These older for the 80s / 90s Spectracom Units did just what you are
looking for.
Unfortunately, they do not work anymore with WWVB as of the phase shift
modulation that was introduced in 2012
Working on a mod for to make them work now a days
here is a link to instruction manual for one of the 8164
https://manuals.repeater-builder.com/te-files/MISCELLANEOUS/Spectracom%208164%20Instruction.pdf
Best,
Mike Fowler
On Mon, Sep 22, 2025 at 10:01 AM john.haine--- via time-nuts <
time-nuts@lists.febo.com> wrote:
Does anyone know of designs for disciplined OCXOs that are referenced to
off-air, especially VLF, signals other than GPS/GNSS please? With modules
for the latter being so cheap this might seem pointless but there are some
potential advantages.
-
GPS reception at indoor locations where mechanical clocks need to
be
monitored is often (usually?) unavailable because of shadowing and building
absorbtion and it's usually inconvenient to run a cable.
-
GPS is increasingly likely to be jammed either by criminal elements
or "state actors".
-
VLF (the likes of WWVB / MSF / DCF77 / e-Loran) is more likely to
be
received indoors.
-
E-Loran is being tipped as an off-air time source to back up GPS
and
will become increasingly available.
-
There's the possibility of a multi-standard receiver that might
find
and lock to any available source, and potentially to several.
Obviously there are a lot of very cheap modules around to receive the
signals but these discard the carrier and just output the time-code logic
signal. I have seen a design for an MSF-locked standard in discrete
components and more recently an MSF receiver implemented as
direct-conversion SDR on a Raspberry Pi Pico which phase locks its internal
digital LO to the carrier but I suspect that its phase noise would be
pretty
ropey - really intended as a time, not frequency, source.
-
John Haine.
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
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To unsubscribe send an email to time-nuts-leave@lists.febo.com
Once upon a time long ago, in a far distant place, I used to watch a signal transmitted by the USN in US, between 50 and 60Hz. This was received with a small, many turned, loop antenna, a preamp, and the 440A Mini. Ubiquitous® FFT analyzer. (That was all there was in those days). A few hundred watts of US located transmitter was unmistakably identifiable on the FFT display, between the 50 and 60 Hz peaks, with a minute or so of integration time. The "bloody" project was abandoned in favor of the current USN VLF transmissions.
Lester B Veenstra K1YCM MØYCM W8YCM 6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1)
lester@veenstras.com
452 Stable Ln
Keyser WV 26726 USA
GPS: 39.336826 N 78.982287 W (Google)
GPS: 39.33682 N 78.9823741 W (GPSDO)
Telephones:
Home: +1-304-289-6057
US cell +1-304-790-9192
Jamaica cell: +1-876-456-8898
-----Original Message-----
From: Deirdre O'Byrne via time-nuts [mailto:time-nuts@lists.febo.com]
Sent: Wednesday, September 24, 2025 6:00 AM
To: Discussion of precise time and frequency measurement
Cc: Deirdre O'Byrne
Subject: [time-nuts] Re: vlf-disciplined OCXO circuit
Anyone thought of, or implemented, a 50/60Hz VLF receiver?
Yes it would have horrible characteristics compared to a proper VLF
station, especially during power cuts. Personally I’m thinking more of
measuring the 50/60Hz “signal” than using it as a time source. And yes I’m
aware that it’s possible to do such measurements by plugging directly into
the grid, but I’d prefer not to do that for reasons.
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
Bob Camp via time-nuts writes:
Part of the “why” was our location. A master station for Loran was way closer than WWVB.
Since the master in a Loran chain transmits at much higher power than the other stations, that’s
the one you want to be near.
Actually, that's not quite correct...
You wanted to track the master because it's Cs clocks were /only/
adjusted to track UTC, whereas the slaves adjusted their Cs's to track
the master as specified under the current circumstances.
Current circumstances included the ionosphere, amount of atmospheric
moisture, amount of ground moisture, snow/ice cover and in one rare
case "somebody built a steel bridge." [source: Prof. Dave Mills.]
It is true that the master transmits more power, nine pulses rather
than eight, but the slave code is balanced, the master code is not.
The imbalance makes the master signal sensitive to "almost perfectly
on frequency" CW signals, and the extra power is nowhere near
enough to compensate for that handicap.
(Even Dave had never been able to find out why the master code was
unbalanced and leaned towards it just being a typo.)
Both the slave adjustments and the CW RFI had taus in the
hour-day range, which was fine if you had a local Cs and not
so fine otherwise.
Poul-Henning
See also: https://phk.freebsd.dk/loran-c/theoretical_spectrum/
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Do I have this right? If the 60 KHz VLF time transmission is phase encoded, can that carrier be at all suitable for maintaining a gps-style standard at 60 KHz?
Don
----- Original Message -----
From: "Poul-Henning Kamp via time-nuts" time-nuts@lists.febo.com
To: "Discussion of precise time and frequency measurement" time-nuts@lists.febo.com
Cc: "Poul-Henning Kamp" phk@phk.freebsd.dk
Sent: Wednesday, September 24, 2025 11:57:43 AM
Subject: [time-nuts] Re: vlf-disciplined OCXO circuit
Bob Camp via time-nuts writes:
Part of the “why” was our location. A master station for Loran was way closer than WWVB.
Since the master in a Loran chain transmits at much higher power than the other stations, that’s
the one you want to be near.
Actually, that's not quite correct...
You wanted to track the master because it's Cs clocks were /only/
adjusted to track UTC, whereas the slaves adjusted their Cs's to track
the master as specified under the current circumstances.
Current circumstances included the ionosphere, amount of atmospheric
moisture, amount of ground moisture, snow/ice cover and in one rare
case "somebody built a steel bridge." [source: Prof. Dave Mills.]
It is true that the master transmits more power, nine pulses rather
than eight, but the slave code is balanced, the master code is not.
The imbalance makes the master signal sensitive to "almost perfectly
on frequency" CW signals, and the extra power is nowhere near
enough to compensate for that handicap.
(Even Dave had never been able to find out why the master code was
unbalanced and leaned towards it just being a typo.)
Both the slave adjustments and the CW RFI had taus in the
hour-day range, which was fine if you had a local Cs and not
so fine otherwise.
Poul-Henning
See also: https://phk.freebsd.dk/loran-c/theoretical_spectrum/
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
Don Latham
PO Box 404,
Frenchtown, MT, 59846
406-626-4304
Am 2025-09-24 12:00, schrieb Deirdre O'Byrne via time-nuts:
Anyone thought of, or implemented, a 50/60Hz VLF receiver?
Yes it would have horrible characteristics compared to a proper VLF
station, especially during power cuts. Personally I’m thinking more of
measuring the 50/60Hz “signal” than using it as a time source. And yes
I’m
aware that it’s possible to do such measurements by plugging directly
into
the grid, but I’d prefer not to do that for reasons.
AC power does not work as a frequency reference because the frequency
is used to synchronize the many generators, so it is a moving target.
It is not always as bad as that:
<
https://www.flickr.com/photos/137684711@N07/38870750440/in/datetaken/
because they could not work out in 2018 who was responsible for blind
power
compensation for some en/exclaves on the Balkans. That made wall clocks
lag some minutes.
Signal preparation was done with a small 5V mains transformer +
attenuator.
The SR-620 did survive. :-)
cheers, Gerhard
In the 1980's, on SSBN submarines, we got a new sensor to track LORAN-C.
This replaced the WPN-3.
We could track traditional multi station LORAN-C, but, we could also
track Phase shift LORAN-C.
While in port we had to track any LORAN-C station for a period of time.
From this we computed the frequency drift of our on board Cesium standard.
This drift rate was entered into the computer.
I do not remember where we got the relative drift rates of the different
LORAN-C stations from, but, this data was also entered into the computer.
From this we could track any two Loran-C stations with our onboard
standard representing the third station.
We did not have to track any master station.
This was one of the fix sources that we use to determine the position of
the submarine to ensure we were within "firing specs" if the order came
to launch.
Glenn Little
ETCS(SS) USN Ret
On 9/24/2025 1:57 PM, Poul-Henning Kamp via time-nuts wrote:
Bob Camp via time-nuts writes:
Part of the “why” was our location. A master station for Loran was way closer than WWVB.
Since the master in a Loran chain transmits at much higher power than the other stations, that’s
the one you want to be near.
Actually, that's not quite correct...
You wanted to track the master because it's Cs clocks were /only/
adjusted to track UTC, whereas the slaves adjusted their Cs's to track
the master as specified under the current circumstances.
Current circumstances included the ionosphere, amount of atmospheric
moisture, amount of ground moisture, snow/ice cover and in one rare
case "somebody built a steel bridge." [source: Prof. Dave Mills.]
It is true that the master transmits more power, nine pulses rather
than eight, but the slave code is balanced, the master code is not.
The imbalance makes the master signal sensitive to "almost perfectly
on frequency" CW signals, and the extra power is nowhere near
enough to compensate for that handicap.
(Even Dave had never been able to find out why the master code was
unbalanced and leaned towards it just being a typo.)
Both the slave adjustments and the CW RFI had taus in the
hour-day range, which was fine if you had a local Cs and not
so fine otherwise.
Poul-Henning
See also: https://phk.freebsd.dk/loran-c/theoretical_spectrum/
--
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@arrl.net AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI, FRA, NRA-LM ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"
sure. The PLL tracking loop in the receiver tracks the carrier phase. A typical Costas loop will work nicely for BPSK.
On Wed, 24 Sep 2025 15:23:57 -0400 (EDT), Don Latham via time-nuts time-nuts@lists.febo.com wrote:
Do I have this right? If the 60 KHz VLF time transmission is phase encoded, can that carrier be at all suitable for maintaining a gps-style standard at 60 KHz?
Don
----- Original Message -----
From: "Poul-Henning Kamp via time-nuts"
To: "Discussion of precise time and frequency measurement"
Cc: "Poul-Henning Kamp"
Sent: Wednesday, September 24, 2025 11:57:43 AM
Subject: [time-nuts] Re: vlf-disciplined OCXO circuit
Bob Camp via time-nuts writes:
Part of the “why” was our location. A master station for Loran was way closer than WWVB.
Since the master in a Loran chain transmits at much higher power than the other stations, that’s
the one you want to be near.
Actually, that's not quite correct...
You wanted to track the master because it's Cs clocks were /only/
adjusted to track UTC, whereas the slaves adjusted their Cs's to track
the master as specified under the current circumstances.
Current circumstances included the ionosphere, amount of atmospheric
moisture, amount of ground moisture, snow/ice cover and in one rare
case "somebody built a steel bridge." [source: Prof. Dave Mills.]
It is true that the master transmits more power, nine pulses rather
than eight, but the slave code is balanced, the master code is not.
The imbalance makes the master signal sensitive to "almost perfectly
on frequency" CW signals, and the extra power is nowhere near
enough to compensate for that handicap.
(Even Dave had never been able to find out why the master code was
unbalanced and leaned towards it just being a typo.)
Both the slave adjustments and the CW RFI had taus in the
hour-day range, which was fine if you had a local Cs and not
so fine otherwise.
Poul-Henning
See also: https://phk.freebsd.dk/loran-c/theoretical_spectrum/
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
Don Latham
PO Box 404,
Frenchtown, MT, 59846
406-626-4304
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To unsubscribe send an email to time-nuts-leave@lists.febo.com
There kind of is a difference, isn’t there, from a FFT or digitally mixing with a sinusoid (generated however). If it’s a pure sinusoid as input, not much difference, but if there’s other signals, all these techniques have different frequency domain passbands (i.e. compare rectangular window vs Hamming vs Blackman, etc.) or, the equivalent, different relative weighting of the time domain samples in the current estimate of the amplitude and phase.
”other signals” here could be things like noise from quantization, from whatever your input receiver looks like, numerical issues (e.g. if you increment an integer counter, then multiply by frequency, then call sin/cos, you’ll get different answers than, say, an incremental CORDIC generator).
For a lot of applications “it doesn’t make any difference” - but here on time-nuts, we do worry about 1E-12 kinds of uncertainties (sometimes… when I set my alarm clock, I’m not worried about 60 second uncertainty, which is 1e-2 kinds of uncertainty)
On Tue, 23 Sep 2025 20:17:34 +0200, dschuecker via time-nuts time-nuts@lists.febo.com wrote:
Hi,
I calculate the amplitude and phase of a sampled signal with the
goertzel algo https://en.wikipedia.org/wiki/Goertzel_algorithm.
It calculates the discrete fourier transform, i.e. amplitude and phase
for a single frequency at the cost of one multiply per sample.
No need to buffer samples.
const float fcc=2.0f*cosf(M_PI/16.0f); // signal freq / sample freq
= 1/32
fq2=0.0f;fq1=0.0f;
for(nn=0;nn0){ // got it
dd=ADC_DR; // get sample
fq0=fq1*fcc-fq2+dd; // undamped second order recursive
filter
fq2=fq1;fq1=fq0;
break;
}
}
}
// unwrap result
double complex z =(float)(fq1-fq2cosf(M_PI/16))+ // Real part
I(float)(fq2*sinf(M_PI/16)); // imaginary part
Cheers
Detlef
Am 22.09.2025 um 19:12 schrieb Poul-Henning Kamp via time-nuts:
john.haine--- via time-nuts writes:
Does anyone know of designs for disciplined OCXOs that are referenced to
off-air, especially VLF, signals other than GPS/GNSS please?
I played a lot with that many years ago.
You can do a lot with a small microcontroller with an ADC which does
something like a million samples per second.
My favourite was this:
Run the ADC at 1 MHz from your reference clock, sum the samples into
a 1000 long circular buffer:
alpha = 1e-5; // play with this
n = 0
while (1) {
x = get_sample()
buffer[x] += (x - buffer[x]) * alpha
x +=1
if x == 1000:
x = 0;
}
This buffer now holds the output of a 1kHz combfilter over your input
signal, which means you can extract the phase and amplitude of any
signal on a multiple of 1kHz from that single buffer.
Simply multiply the 1000 samples in the buffer with sin() and cos()
of your desired frequency and calculate the magnitude and angle of
the resulting vector:
fx = 60 // 60 khz
ssin = 0.0
scos = 0.0
for i in range(1000):
ssin += sin(2 * PI * i / 1000 * buffer[i]
scos += sin(2 * PI * i / 1000 * buffer[i]
ampl = hypot(ssin, scos)
angle = atan2(ssin, scos)
Now do that for as many signals as you want, and steer your
reference clock accordingly.
If you want to also track signals on half kHz (like DCF77), make
the buffer 2000 samples.
One paticularly interesting case is using a buffer exactly one
second long (=1 million in this example), that would allow you
to extract both the phase and the modulation from signals
like DCF77 and WWVB
The Pi2 has a 500kS ADC and two CPU cores, so it is nearly perfect,
provided you can lock the frequency to your house standard - or
just use an external ADC, plenty of eval boards out there.
I didn't document very much of the fun I had, but there is
some stuff here:
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Many thanks for all the responses! A few random thoughts in response.
- I'm based in the eastern UK near Cambridge. Anthorn where the only
"nearby" eLoran station, and also MSF, is 370 km / 230 miles. Mainflingen
(DCF77) is 666 km/ 535 miles. DCF77 signals are largely available in the UK
and most of the cheap RC clocks use them. However in some locations they
are a bit dodgy - for example Bristol University where I sometimes work put
RC clocks in most public areas and they are often wrong or spend all their
time trying to re-sync. MSF and eLoran would work better I suspect though
consumer MSF receivers are less available as the market is more UK-based
while DCF 77 works over most of Europe. - Using an online SDR based in Bedford which is 40 miles of so west of
here eLoran from Anthorn is quite strong but DCF and MSF not observable -
that may be the antennas used as much as anything. - Unlike WWVB MSF does not have a phase modulation component, and its
carrier is switched off completely by the keying. Phase locking to its
carrier therefore has to gate the PLL but there is one design at least that
does this. - DCF77 has a spread-spectrum phase mod component and its carrier is
not switched off completely. This makes it much more robust if a properly
designed coherent receiver is used and I've seen one design that does this
in software. Unfortunately - I wasn't aware that eLoran has a phase mod component, I need to read
up on its waveform design more. But is being toted as a GPS/GNSS backup for
timing in Europe where we have a large and unfriendly neighbour.
I'll study the responses in more detail and follow up if this project makes
it to the starting blocks.
Thanks everyone for your input!
- John
-----Original Message-----
From: john.haine--- via time-nuts time-nuts@lists.febo.com
Sent: 22 September 2025 10:20
To: 'Discussion of precise time and frequency measurement'
time-nuts@lists.febo.com
Cc: john.haine@haine-online.net
Subject: [time-nuts] vlf-disciplined OCXO circuit
Does anyone know of designs for disciplined OCXOs that are referenced to
off-air, especially VLF, signals other than GPS/GNSS please? With modules
for the latter being so cheap this might seem pointless but there are some
potential advantages.
- GPS reception at indoor locations where mechanical clocks need to be
monitored is often (usually?) unavailable because of shadowing and building
absorbtion and it's usually inconvenient to run a cable. - GPS is increasingly likely to be jammed either by criminal elements
or "state actors". - VLF (the likes of WWVB / MSF / DCF77 / e-Loran) is more likely to be
received indoors. - E-Loran is being tipped as an off-air time source to back up GPS and
will become increasingly available. - There's the possibility of a multi-standard receiver that might find
and lock to any available source, and potentially to several.
Obviously there are a lot of very cheap modules around to receive the
signals but these discard the carrier and just output the time-code logic
signal. I have seen a design for an MSF-locked standard in discrete
components and more recently an MSF receiver implemented as
direct-conversion SDR on a Raspberry Pi Pico which phase locks its internal
digital LO to the carrier but I suspect that its phase noise would be pretty
ropey - really intended as a time, not frequency, source.
- John Haine.
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