vlf-disciplined OCXO circuit
Hi
Yes and no. As noted earlier you can double the carrier and lock to that.
One basic issue with 60 KHz is phase slips. You really want to ID the “cycle” you are tracking. Loran gear does this all the time. Doing that with WWVB a bit of a challenge.
How much of an issue are phase slips on WWVB? It depends a lot on where you are in the US. If we’re talking about MSF on 60 KHz, most folks in the UK aren’t quite as far from the transmitter as the major population centers in the US are from WWVB.
I’m guessing we’re talking about WWVB and you are somewhere in the US. If you are in the north east, decoding the modulation has the added benefit of sorting out interference from MSF. It also helps a bit with sorting out all of the RFI from the vast number of things running 60KHz switching power supplies (and no filtering ….).
To have something reasonably reliable you probably will be decoding the modulation. These days some sort of SDR is likely to be involved along with some processing somewhere. Tossing in modulation decoding is “just code” :) :).
Bob
On Sep 24, 2025, at 3:23 PM, 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" 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/
--
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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.
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Frenchtown, MT, 59846
406-626-4304
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Hi,
I tried with a 262144 samples 'pure' ( 8 bytes for a double ) sinewave.
1.310720000000000e+05 - 1.314745628841594e-07i for FFT
1.310730000003061e+05 + 1.651948562937711e-06i for Goertzel
1.310719999999999e+05 - 3.865352482534945e-11i for mixing with a
complex 'carrier'
Now the sine with additional ~ -17dB broadband white noise
1.310543992827178e+05 - 1.285247212381880e+01i FFT
1.310554051787366e+05 - 1.285247050053514e+01i Goertzel
1.310543992827178e+05 + 1.285247199235141e+01i Mixing
I cannot see great difference in the noise impact. But that is only a guess.
I never had numerical issues with FFT or Goertzel or mixing. For 1E-12 a
32-Bit float is not sufficient, a 64-Bit is. For very sharp IIR-filters
you need more than 64 Bit.
Cheers
Detlef
clear
n=2^18;
sig=cos(2pi(n/32)(0:n-1)/n);
noi=0.1randn(1,n);
sigsig.'
noinoi.'
10log10((sigsig.')/(noi*noi.'))
sig=sig+noi;
spsig=fft(sig);
format long
spsig(8193)
M_PI = pi;
fcc=2.0*cos(M_PI/16.0);
fq2=0.0;fq1=0.0;
noi1 =[noi noi(1)];
for(k=1:n+1)
%dd=sig(k);
dd=cos(2pi(n/32)(k-1)/n)+noi1(k);
fq0=fq1fcc-fq2+dd;
fq2=fq1;fq1=fq0;
end
z =(fq1-fq2cos(M_PI/16))+ i(fq2*sin(M_PI/16))
sigexp(i(2pi(n/32)*(0:n-1)/n)).'
return
Am 25.09.2025 um 11:49 schrieb Jim Lux via time-nuts:
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 WWVBThe 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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In case it's relevant ..
I'm in Bedford (I'm not the operator of that SDR though).
I've got a little heap of receivers in case they're interesting for
comparison, loan etc. A radio-4-LW-disciplined oscillator, a Thunderbolt, a
heap of KS-24361 ref 0 GPSDOs, and (not connected) an MSF time receiver, a
Pluto SDR and a Rubidium oscillator.
I also have some random MSF and DCF77 clocks around. The MSF clocks work
pretty well but the DCF77 kitchen clock jumps a couple of hours sometimes
then jumps back a couple of days later. The MSF clock used to get upset by
a VGA monitor when it was close by. Doesn't seem to mind modern LCD ones.
I believe the LW-disciplined oscillator is on borrowed time. The device is
fine but the LW transmitter is in danger of being retired any time soon.
On Thu, Sep 25, 2025 at 1:35 PM john.haine--- via time-nuts <
time-nuts@lists.febo.com> wrote:
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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In addition to all that has been said above, the WWVB phase modulation
schema always sends the last bit (last second) of the minute as a
known/fixed phase reference, so you do have a way to detect half cycle
phase slips, or to do a gated phase reference for controlling a secondary
oscillator.
--- Graham
==
On Thu, Sep 25, 2025 at 12:10 PM Bob Camp via time-nuts <
time-nuts@lists.febo.com> wrote:
Hi
Yes and no. As noted earlier you can double the carrier and lock to that.
One basic issue with 60 KHz is phase slips. You really want to ID the
“cycle” you are tracking. Loran gear does this all the time. Doing that
with WWVB a bit of a challenge.
How much of an issue are phase slips on WWVB? It depends a lot on where
you are in the US. If we’re talking about MSF on 60 KHz, most folks in the
UK aren’t quite as far from the transmitter as the major population centers
in the US are from WWVB.
I’m guessing we’re talking about WWVB and you are somewhere in the US. If
you are in the north east, decoding the modulation has the added benefit of
sorting out interference from MSF. It also helps a bit with sorting out all
of the RFI from the vast number of things running 60KHz switching power
supplies (and no filtering ….).
To have something reasonably reliable you probably will be decoding the
modulation. These days some sort of SDR is likely to be involved along with
some processing somewhere. Tossing in modulation decoding is “just code” :)
:).
Bob
On Sep 24, 2025, at 3:23 PM, 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" time-nuts@lists.febo.com
To: "Discussion of precise time and frequency measurement" <
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
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Now put some noise in the system? Or a quantized input (which is in some sense just another noise)? Or an interfering signal with a frequency a bit off from the signal of interest.
That’s where the “window” or “filter shape” starts to make a difference,
On Thu, 25 Sep 2025 16:20:37 +0200, dschuecker via time-nuts time-nuts@lists.febo.com wrote:
Hi,
I tried with a 262144 samples 'pure' ( 8 bytes for a double ) sinewave.
1.310720000000000e+05 - 1.314745628841594e-07i for FFT
1.310730000003061e+05 + 1.651948562937711e-06i for Goertzel
1.310719999999999e+05 - 3.865352482534945e-11i for mixing with a
complex 'carrier'
Now the sine with additional ~ -17dB broadband white noise
1.310543992827178e+05 - 1.285247212381880e+01i FFT
1.310554051787366e+05 - 1.285247050053514e+01i Goertzel
1.310543992827178e+05 + 1.285247199235141e+01i Mixing
I cannot see great difference in the noise impact. But that is only a guess.
I never had numerical issues with FFT or Goertzel or mixing. For 1E-12 a
32-Bit float is not sufficient, a 64-Bit is. For very sharp IIR-filters
you need more than 64 Bit.
Cheers
Detlef
clear
n=2^18;
sig=cos(2pi(n/32)(0:n-1)/n);
noi=0.1randn(1,n);
sigsig.'
noinoi.'
10log10((sigsig.')/(noi*noi.'))
sig=sig+noi;
spsig=fft(sig);
format long
spsig(8193)
M_PI = pi;
fcc=2.0*cos(M_PI/16.0);
fq2=0.0;fq1=0.0;
noi1 =[noi noi(1)];
for(k=1:n+1)
%dd=sig(k);
dd=cos(2pi(n/32)(k-1)/n)+noi1(k);
fq0=fq1fcc-fq2+dd;
fq2=fq1;fq1=fq0;
end
z =(fq1-fq2cos(M_PI/16))+ i(fq2*sin(M_PI/16))
sigexp(i(2pi(n/32)*(0:n-1)/n)).'
return
Am 25.09.2025 um 11:49 schrieb Jim Lux via time-nuts:
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 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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Hi
There are an unfortunate lot of things out there that can take out a 60KHz VLF signal. For cost
reasons, 60kHz is what a lot of low end switchers run at. They are not controlled in any way so
that’s a very approximate number. Since they are typically hooked to the power line, they have a
fine “antenna” to work with. If you count the number of this and that in the typical home, there might
well be a hundred devices with switchers in them. They won’t all be on at once. All it takes is one
“bad one” running every so often to really make a mess.
If you grab one of these things and take a look with a spectrum analyzer: You typically see a pretty
big spike at whatever frequency it happens to like today as well as harmonics of that frequency. In
addition, there is a fairly broad set of “crud sidebands” that cover a wide range at a lower level. It
also should be noted that there are lots of ways they do this (even just at 60 KHz). Each one
has it’s own “signature”.
If you are way out on a farm somewhere, you might only have to deal with your own devices. In
a typical urban setting, you have a lot more than just your own devices to worry about.
Not every “bad one” will be equally bad. Some will bother things in a pretty small area. Others just
might cover a pretty wide area.
There’s also somewhat more difficult things that do come up. This or that device is hooked to
something stable. It just happens to have a spur at 60KHz. This is not very common. The issue
here is that the “threat signal” is a pretty stable carrier. Somebody putting up a local “60 KHz home
transmitter” to run their wall clocks? It does indeed happen.
Since this is all a bit random, what works today may not work tomorrow. Equally, that gizmo that
made it impossible for months just might burn out. Putting a lot of time and money into something
like this only to find it destroyed by “something” is not a good outcome.
Are there rules ( ok laws) about this stuff? Sure there are. None of this should be going on. Much
of the compliance testing and certification is done in a pretty informal manner (there is no outside
lab involved). Some folks will always be a bit less worried about this than others.
From doing this in the past, I’d plan for an outdoor antenna. Get it as far from the power lines and
any dwellings as you can. Even with an indoor antenna, getting it as far from power and “other stuff”
is a really good idea.
Fun!!
Bob
On Sep 25, 2025, at 1:33 PM, Adrian Godwin via time-nuts time-nuts@lists.febo.com wrote:
In case it's relevant ..
I'm in Bedford (I'm not the operator of that SDR though).
I've got a little heap of receivers in case they're interesting for
comparison, loan etc. A radio-4-LW-disciplined oscillator, a Thunderbolt, a
heap of KS-24361 ref 0 GPSDOs, and (not connected) an MSF time receiver, a
Pluto SDR and a Rubidium oscillator.
I also have some random MSF and DCF77 clocks around. The MSF clocks work
pretty well but the DCF77 kitchen clock jumps a couple of hours sometimes
then jumps back a couple of days later. The MSF clock used to get upset by
a VGA monitor when it was close by. Doesn't seem to mind modern LCD ones.
I believe the LW-disciplined oscillator is on borrowed time. The device is
fine but the LW transmitter is in danger of being retired any time soon.
On Thu, Sep 25, 2025 at 1:35 PM john.haine--- via time-nuts <
time-nuts@lists.febo.com> wrote:
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.
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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To unsubscribe send an email to time-nuts-leave@lists.febo.com
As it happens, lately I've been working on the following project:
Building a 'retro' decoder for the WWVB time signal, based on a Motorola
6800-series MCU (actually a 6803). It gets its input from a Spectracom
8161, which outputs TTL-level bits detected from the 60 KHz antenna input.
Just this morning I got the basic pulse-width measurement code working
correctly, to detect the 0's, 1's, and Marker pulses.
At the moment, my antenna is a few feet of wire. I'm only about 120 miles
from Ft. Collins, so I get plenty of signal. However, the signal is "messed
with" by the issues that Bob and others have described. So I get a lot of
pulses of the wrong width.
I'll try a small ferrite loop antenna, to see if it cleans things up.
After I can decode WWVB reliably, I'll add code to output the old NASA and
IRIG-B 1-second time codes.
Pete
On Fri, Sep 26, 2025 at 7:29 AM Bob Camp via time-nuts <
time-nuts@lists.febo.com> wrote:
Hi
There are an unfortunate lot of things out there that can take out a 60KHz
VLF signal. For cost
reasons, 60kHz is what a lot of low end switchers run at. They are not
controlled in any way so
that’s a very approximate number. Since they are typically hooked to the
power line, they have a
fine “antenna” to work with. If you count the number of this and that in
the typical home, there might
well be a hundred devices with switchers in them. They won’t all be on at
once. All it takes is one
“bad one” running every so often to really make a mess.
If you grab one of these things and take a look with a spectrum analyzer:
You typically see a pretty
big spike at whatever frequency it happens to like today as well as
harmonics of that frequency. In
addition, there is a fairly broad set of “crud sidebands” that cover a
wide range at a lower level. It
also should be noted that there are lots of ways they do this (even just
at 60 KHz). Each one
has it’s own “signature”.
If you are way out on a farm somewhere, you might only have to deal with
your own devices. In
a typical urban setting, you have a lot more than just your own devices to
worry about.
Not every “bad one” will be equally bad. Some will bother things in a
pretty small area. Others just
might cover a pretty wide area.
There’s also somewhat more difficult things that do come up. This or that
device is hooked to
something stable. It just happens to have a spur at 60KHz. This is not
very common. The issue
here is that the “threat signal” is a pretty stable carrier. Somebody
putting up a local “60 KHz home
transmitter” to run their wall clocks? It does indeed happen.
Since this is all a bit random, what works today may not work tomorrow.
Equally, that gizmo that
made it impossible for months just might burn out. Putting a lot of time
and money into something
like this only to find it destroyed by “something” is not a good outcome.
Are there rules ( ok laws) about this stuff? Sure there are. None of this
should be going on. Much
of the compliance testing and certification is done in a pretty informal
manner (there is no outside
lab involved). Some folks will always be a bit less worried about this
than others.
From doing this in the past, I’d plan for an outdoor antenna. Get it as
far from the power lines and
any dwellings as you can. Even with an indoor antenna, getting it as far
from power and “other stuff”
is a really good idea.
Fun!!
Bob
On Sep 25, 2025, at 1:33 PM, Adrian Godwin via time-nuts <
time-nuts@lists.febo.com> wrote:
In case it's relevant ..
I'm in Bedford (I'm not the operator of that SDR though).
I've got a little heap of receivers in case they're interesting for
comparison, loan etc. A radio-4-LW-disciplined oscillator, a
Thunderbolt, a
heap of KS-24361 ref 0 GPSDOs, and (not connected) an MSF time receiver,
a
Pluto SDR and a Rubidium oscillator.
I also have some random MSF and DCF77 clocks around. The MSF clocks work
pretty well but the DCF77 kitchen clock jumps a couple of hours sometimes
then jumps back a couple of days later. The MSF clock used to get upset
by
a VGA monitor when it was close by. Doesn't seem to mind modern LCD ones.
I believe the LW-disciplined oscillator is on borrowed time. The device
is
fine but the LW transmitter is in danger of being retired any time soon.
On Thu, Sep 25, 2025 at 1:35 PM john.haine--- via time-nuts <
time-nuts@lists.febo.com> wrote:
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.
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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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
Way back when I was a consultant I had to troubleshoot a badly executed consumer electronics project that included an AM/FM broadcast receiver amongst other elements. This was installed in the central control panel of a built-in vacuum cleaner system (!), the idea being that radio programmes could be listened to throughout a house. The receiver used a truly awful LF/MF rf module with a high impedance input and zero input selectivity. The "antenna" was a bit of wire hanging out the back of the product enclosure (itself installed into the wall of the house). LF/MF reception was totally impossible in nearly every location due to a loud interference "hash" clearly emanating from the mains. However an ordinary portable radio in the same location usually worked absolutely fine. Eventually found that the short "capacitive" antenna (i.e. the wire) picked up strong impulsive near-E-field interference from things like fluorescent tubes etc, whilst the inductive loop antenna in an ordinary radio was relatively immune from this. The only way we found to solve the problem was to install an external antenna which was pretty ugly with an existing installation in a house.
So a ferrite loop antenna, preferably tuned, may help a lot, as would a crystal filter as generally used in consumer RC clocks. If you can find an application note for the chips they use it should include a circuit.
-----Original Message-----
From: Peter McCollum via time-nuts time-nuts@lists.febo.com
Sent: 26 September 2025 16:10
To: Discussion of precise time and frequency measurement time-nuts@lists.febo.com
Cc: Peter McCollum saipan1959@gmail.com
Subject: [time-nuts] Re: vlf-disciplined OCXO circuit
As it happens, lately I've been working on the following project:
Building a 'retro' decoder for the WWVB time signal, based on a Motorola 6800-series MCU (actually a 6803). It gets its input from a Spectracom 8161, which outputs TTL-level bits detected from the 60 KHz antenna input.
Just this morning I got the basic pulse-width measurement code working correctly, to detect the 0's, 1's, and Marker pulses.
At the moment, my antenna is a few feet of wire. I'm only about 120 miles from Ft. Collins, so I get plenty of signal. However, the signal is "messed with" by the issues that Bob and others have described. So I get a lot of pulses of the wrong width.
I'll try a small ferrite loop antenna, to see if it cleans things up.
After I can decode WWVB reliably, I'll add code to output the old NASA and IRIG-B 1-second time codes.
Pete
On Fri, Sep 26, 2025 at 7:29 AM Bob Camp via time-nuts < time-nuts@lists.febo.com> wrote:
Hi
There are an unfortunate lot of things out there that can take out a
60KHz VLF signal. For cost reasons, 60kHz is what a lot of low end
switchers run at. They are not controlled in any way so that’s a very
approximate number. Since they are typically hooked to the power line,
they have a fine “antenna” to work with. If you count the number of
this and that in the typical home, there might well be a hundred
devices with switchers in them. They won’t all be on at once. All it
takes is one “bad one” running every so often to really make a mess.
If you grab one of these things and take a look with a spectrum analyzer:
You typically see a pretty
big spike at whatever frequency it happens to like today as well as
harmonics of that frequency. In addition, there is a fairly broad set
of “crud sidebands” that cover a wide range at a lower level. It also
should be noted that there are lots of ways they do this (even just at
60 KHz). Each one has it’s own “signature”.
If you are way out on a farm somewhere, you might only have to deal
with your own devices. In a typical urban setting, you have a lot more
than just your own devices to worry about.
Not every “bad one” will be equally bad. Some will bother things in a
pretty small area. Others just might cover a pretty wide area.
There’s also somewhat more difficult things that do come up. This or
that device is hooked to something stable. It just happens to have a
spur at 60KHz. This is not very common. The issue here is that the
“threat signal” is a pretty stable carrier. Somebody putting up a
local “60 KHz home transmitter” to run their wall clocks? It does
indeed happen.
Since this is all a bit random, what works today may not work tomorrow.
Equally, that gizmo that
made it impossible for months just might burn out. Putting a lot of
time and money into something like this only to find it destroyed by
“something” is not a good outcome.
Are there rules ( ok laws) about this stuff? Sure there are. None of
this should be going on. Much of the compliance testing and
certification is done in a pretty informal manner (there is no outside
lab involved). Some folks will always be a bit less worried about this
than others.
From doing this in the past, I’d plan for an outdoor antenna. Get it
as far from the power lines and any dwellings as you can. Even with an
indoor antenna, getting it as far from power and “other stuff”
is a really good idea.
Fun!!
Bob
On Sep 25, 2025, at 1:33 PM, Adrian Godwin via time-nuts <
time-nuts@lists.febo.com> wrote:
In case it's relevant ..
I'm in Bedford (I'm not the operator of that SDR though).
I've got a little heap of receivers in case they're interesting for
comparison, loan etc. A radio-4-LW-disciplined oscillator, a
Thunderbolt, a
heap of KS-24361 ref 0 GPSDOs, and (not connected) an MSF time
receiver,
a
Pluto SDR and a Rubidium oscillator.
I also have some random MSF and DCF77 clocks around. The MSF clocks
work pretty well but the DCF77 kitchen clock jumps a couple of hours
sometimes then jumps back a couple of days later. The MSF clock used
to get upset
by
a VGA monitor when it was close by. Doesn't seem to mind modern LCD ones.
I believe the LW-disciplined oscillator is on borrowed time. The
device
is
fine but the LW transmitter is in danger of being retired any time soon.
On Thu, Sep 25, 2025 at 1:35 PM john.haine--- via time-nuts <
time-nuts@lists.febo.com> wrote:
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.
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
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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an email to time-nuts-leave@lists.febo.com
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Hi
I think you probably should look at what PHK did a while back on his “VLF setup”.
He addressed the whole “noise comes and goes” thing very well with what he did.
For a single data stream, you just might fit it in a 6803 …. maybe.
Bob
On Sep 26, 2025, at 11:10 AM, Peter McCollum via time-nuts time-nuts@lists.febo.com wrote:
As it happens, lately I've been working on the following project:
Building a 'retro' decoder for the WWVB time signal, based on a Motorola
6800-series MCU (actually a 6803). It gets its input from a Spectracom
8161, which outputs TTL-level bits detected from the 60 KHz antenna input.
Just this morning I got the basic pulse-width measurement code working
correctly, to detect the 0's, 1's, and Marker pulses.
At the moment, my antenna is a few feet of wire. I'm only about 120 miles
from Ft. Collins, so I get plenty of signal. However, the signal is "messed
with" by the issues that Bob and others have described. So I get a lot of
pulses of the wrong width.
I'll try a small ferrite loop antenna, to see if it cleans things up.
After I can decode WWVB reliably, I'll add code to output the old NASA and
IRIG-B 1-second time codes.
Pete
On Fri, Sep 26, 2025 at 7:29 AM Bob Camp via time-nuts <
time-nuts@lists.febo.com> wrote:
Hi
There are an unfortunate lot of things out there that can take out a 60KHz
VLF signal. For cost
reasons, 60kHz is what a lot of low end switchers run at. They are not
controlled in any way so
that’s a very approximate number. Since they are typically hooked to the
power line, they have a
fine “antenna” to work with. If you count the number of this and that in
the typical home, there might
well be a hundred devices with switchers in them. They won’t all be on at
once. All it takes is one
“bad one” running every so often to really make a mess.
If you grab one of these things and take a look with a spectrum analyzer:
You typically see a pretty
big spike at whatever frequency it happens to like today as well as
harmonics of that frequency. In
addition, there is a fairly broad set of “crud sidebands” that cover a
wide range at a lower level. It
also should be noted that there are lots of ways they do this (even just
at 60 KHz). Each one
has it’s own “signature”.
If you are way out on a farm somewhere, you might only have to deal with
your own devices. In
a typical urban setting, you have a lot more than just your own devices to
worry about.
Not every “bad one” will be equally bad. Some will bother things in a
pretty small area. Others just
might cover a pretty wide area.
There’s also somewhat more difficult things that do come up. This or that
device is hooked to
something stable. It just happens to have a spur at 60KHz. This is not
very common. The issue
here is that the “threat signal” is a pretty stable carrier. Somebody
putting up a local “60 KHz home
transmitter” to run their wall clocks? It does indeed happen.
Since this is all a bit random, what works today may not work tomorrow.
Equally, that gizmo that
made it impossible for months just might burn out. Putting a lot of time
and money into something
like this only to find it destroyed by “something” is not a good outcome.
Are there rules ( ok laws) about this stuff? Sure there are. None of this
should be going on. Much
of the compliance testing and certification is done in a pretty informal
manner (there is no outside
lab involved). Some folks will always be a bit less worried about this
than others.
From doing this in the past, I’d plan for an outdoor antenna. Get it as
far from the power lines and
any dwellings as you can. Even with an indoor antenna, getting it as far
from power and “other stuff”
is a really good idea.
Fun!!
Bob
On Sep 25, 2025, at 1:33 PM, Adrian Godwin via time-nuts <
time-nuts@lists.febo.com> wrote:
In case it's relevant ..
I'm in Bedford (I'm not the operator of that SDR though).
I've got a little heap of receivers in case they're interesting for
comparison, loan etc. A radio-4-LW-disciplined oscillator, a
Thunderbolt, a
heap of KS-24361 ref 0 GPSDOs, and (not connected) an MSF time receiver,
a
Pluto SDR and a Rubidium oscillator.
I also have some random MSF and DCF77 clocks around. The MSF clocks work
pretty well but the DCF77 kitchen clock jumps a couple of hours sometimes
then jumps back a couple of days later. The MSF clock used to get upset
by
a VGA monitor when it was close by. Doesn't seem to mind modern LCD ones.
I believe the LW-disciplined oscillator is on borrowed time. The device
is
fine but the LW transmitter is in danger of being retired any time soon.
On Thu, Sep 25, 2025 at 1:35 PM john.haine--- via time-nuts <
time-nuts@lists.febo.com> wrote:
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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Update on my project, for those that might be interested.
I spent the last day struggling with my MCU code and the Spectracom 8161.
The 8161 seemed to be outputting bad WWVB data, but I couldn't be sure if
it was my poor antenna, a code problem in my MCU, or a problem in the 8161.
Then I remembered that I have one of those C-MAX WWVB receiver modules
providing the TOD for my in-house 'telemetry network'. So I used a scope to
do a side-by-side compare of the C-MAX with the 8161. Sure enough, the 8161
was outputting a LOT of bad data (it would only occasionally do the correct
bits). Studied the 8161 design some more, and realized that its ability to
do the time-code output was dependent on a phase comparison with the VCO
(this is NOT the ovenized VCO 'standard', which is also in the box). But
the VCO is never properly locked to the WWVB carrier, because of the
phase-change issue about 10(?) years ago. The AGC on the 60 KHz receiver
was constantly moving around, therefore messing with the bit detection and
such.
SO, I removed the phase-detector chip (socketed) that handles the AGC and
time-code stuff, and replaced it with a simple AM detector (a diode,
transistor, two R's and a C).
It works! After one final tweak to my code, my 6803 MCU gadget is
displaying UTC!
And my simple long-wire antenna is working fine, also.
Pete
On Sat, Sep 27, 2025 at 4:10 AM john.haine@haine-online.net wrote:
Way back when I was a consultant I had to troubleshoot a badly executed
consumer electronics project that included an AM/FM broadcast receiver
amongst other elements. This was installed in the central control panel of
a built-in vacuum cleaner system (!), the idea being that radio programmes
could be listened to throughout a house. The receiver used a truly awful
LF/MF rf module with a high impedance input and zero input selectivity.
The "antenna" was a bit of wire hanging out the back of the product
enclosure (itself installed into the wall of the house). LF/MF reception
was totally impossible in nearly every location due to a loud interference
"hash" clearly emanating from the mains. However an ordinary portable
radio in the same location usually worked absolutely fine. Eventually
found that the short "capacitive" antenna (i.e. the wire) picked up strong
impulsive near-E-field interference from things like fluorescent tubes
etc, whilst the inductive loop antenna in an ordinary radio was relatively
immune from this. The only way we found to solve the problem was to
install an external antenna which was pretty ugly with an existing
installation in a house.
So a ferrite loop antenna, preferably tuned, may help a lot, as would a
crystal filter as generally used in consumer RC clocks. If you can find an
application note for the chips they use it should include a circuit.
-----Original Message-----
From: Peter McCollum via time-nuts time-nuts@lists.febo.com
Sent: 26 September 2025 16:10
To: Discussion of precise time and frequency measurement <
time-nuts@lists.febo.com>
Cc: Peter McCollum saipan1959@gmail.com
Subject: [time-nuts] Re: vlf-disciplined OCXO circuit
As it happens, lately I've been working on the following project:
Building a 'retro' decoder for the WWVB time signal, based on a Motorola
6800-series MCU (actually a 6803). It gets its input from a Spectracom
8161, which outputs TTL-level bits detected from the 60 KHz antenna input.
Just this morning I got the basic pulse-width measurement code working
correctly, to detect the 0's, 1's, and Marker pulses.
At the moment, my antenna is a few feet of wire. I'm only about 120 miles
from Ft. Collins, so I get plenty of signal. However, the signal is "messed
with" by the issues that Bob and others have described. So I get a lot of
pulses of the wrong width.
I'll try a small ferrite loop antenna, to see if it cleans things up.
After I can decode WWVB reliably, I'll add code to output the old NASA and
IRIG-B 1-second time codes.
Pete
On Fri, Sep 26, 2025 at 7:29 AM Bob Camp via time-nuts <
time-nuts@lists.febo.com> wrote:
Hi
There are an unfortunate lot of things out there that can take out a
60KHz VLF signal. For cost reasons, 60kHz is what a lot of low end
switchers run at. They are not controlled in any way so that’s a very
approximate number. Since they are typically hooked to the power line,
they have a fine “antenna” to work with. If you count the number of
this and that in the typical home, there might well be a hundred
devices with switchers in them. They won’t all be on at once. All it
takes is one “bad one” running every so often to really make a mess.
If you grab one of these things and take a look with a spectrum analyzer:
You typically see a pretty
big spike at whatever frequency it happens to like today as well as
harmonics of that frequency. In addition, there is a fairly broad set
of “crud sidebands” that cover a wide range at a lower level. It also
should be noted that there are lots of ways they do this (even just at
60 KHz). Each one has it’s own “signature”.
If you are way out on a farm somewhere, you might only have to deal
with your own devices. In a typical urban setting, you have a lot more
than just your own devices to worry about.
Not every “bad one” will be equally bad. Some will bother things in a
pretty small area. Others just might cover a pretty wide area.
There’s also somewhat more difficult things that do come up. This or
that device is hooked to something stable. It just happens to have a
spur at 60KHz. This is not very common. The issue here is that the
“threat signal” is a pretty stable carrier. Somebody putting up a
local “60 KHz home transmitter” to run their wall clocks? It does
indeed happen.
Since this is all a bit random, what works today may not work tomorrow.
Equally, that gizmo that
made it impossible for months just might burn out. Putting a lot of
time and money into something like this only to find it destroyed by
“something” is not a good outcome.
Are there rules ( ok laws) about this stuff? Sure there are. None of
this should be going on. Much of the compliance testing and
certification is done in a pretty informal manner (there is no outside
lab involved). Some folks will always be a bit less worried about this
than others.
From doing this in the past, I’d plan for an outdoor antenna. Get it
as far from the power lines and any dwellings as you can. Even with an
indoor antenna, getting it as far from power and “other stuff”
is a really good idea.
Fun!!
Bob
On Sep 25, 2025, at 1:33 PM, Adrian Godwin via time-nuts <
time-nuts@lists.febo.com> wrote:
In case it's relevant ..
I'm in Bedford (I'm not the operator of that SDR though).
I've got a little heap of receivers in case they're interesting for
comparison, loan etc. A radio-4-LW-disciplined oscillator, a
Thunderbolt, a
heap of KS-24361 ref 0 GPSDOs, and (not connected) an MSF time
receiver,
a
Pluto SDR and a Rubidium oscillator.
I also have some random MSF and DCF77 clocks around. The MSF clocks
work pretty well but the DCF77 kitchen clock jumps a couple of hours
sometimes then jumps back a couple of days later. The MSF clock used
to get upset
by
a VGA monitor when it was close by. Doesn't seem to mind modern LCD
ones.
I believe the LW-disciplined oscillator is on borrowed time. The
device
is
fine but the LW transmitter is in danger of being retired any time
soon.
On Thu, Sep 25, 2025 at 1:35 PM john.haine--- via time-nuts <
time-nuts@lists.febo.com> wrote:
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.
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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