Re: [time-nuts] WWV Receivers

[Chris Albertson]

On Mon, Feb 6, 2017 at 11:27 PM, Hal Murray  wrote:

>
> > esp. if one uses a Chinese $6.50 incl. shipping HF  receiver off eBay;
>
> Could somebody give me a lesson in receivers appropriate for extracting
> time
> from WWV?
>
> Is $10 a realistic price?
>

Yes, this would not need to be tunable as WWV is at a fixed frequency.  I
have seen a receiver that uses a 10MHz crystal in the front end and then
mixes the signal to baseband then samples it with a PC "sound card".   $10
in parts easy

You extract the time in the PC software.   I say "PC" but a really low-end
computer like a Rasperry Pi would be perfect for this, maybe over kill but
you'd want the features of the OS to send the time some place
-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] WWV Receivers

[Poul-Henning Kamp]

In message <20170207072741.b084f406...@ip-64-139-1-69.sjc.megapath.net>, Hal 
Murray writes:
>
>> esp. if one uses a Chinese $6.50 incl. shipping HF  receiver off eBay;
>
>Could somebody give me a lesson in receivers appropriate for extracting time 
>from WWV?

Somebody should do an SDR project for this.

Modern microcontrollers have ADC's which are capable of sampling fast
enough and plenty of processing power to demodulate all the parts,
including the phase modulation.

Clock the microcontroller of your house-standard and you have a pretty
good sanity-check on your GPS receivers.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@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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[time-nuts] WWV Receivers

[Hal Murray]

> esp. if one uses a Chinese $6.50 incl. shipping HF  receiver off eBay;

Could somebody give me a lesson in receivers appropriate for extracting time 
from WWV?

Is $10 a realistic price?


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] WWV receivers?

[Chris Albertson]

There is zero jitter through the SDR software because you can always buffer
the output and then reclock it on output and all you have to deal with is a
known fixed delay.  If the samples are clocked in accurately that is all
you need.

Some audio interfaces have can have very good timing and run off an
external reference oscillator.  But those are typically found in
professional studios.  (Some studios have coax or fiber frequency
distribution.) But The typical home studio audio interface that sells for
under $200 uses a four pin  oscillator.

The bigger question is propagation.



On Sat, Oct 29, 2016 at 12:07 PM, Attila Kinali  wrote:

> On Sat, 29 Oct 2016 09:35:25 -0700
> jimlux  wrote:
>
> > > Should not be too high. If Jeff Sherman's and Robert Jörden's paper[1]
> > > is any indication, then the jitter should be dominated by the jitter
> > > of the ADC and its reference oscillator. So sub-ps, order of 100fs
> jitter
> > > should be possible with proper design. Long term drift is another issue
> > > and I have not completely figured out what are the contributors there.
> > > Temperature stabilizing for sure helps, but it doesn't seem to be the
> > > only effect.
> >
> >
> > Well, that's "jitter in the original samples" which can be very low, as
> > you describe. But I would interpret the original question as "jitter
> > *through* an SDR" which implies that we're looking at the timing of
> > output vs input.
>
> Oh.. yes...The whole latency into the PC is a whole different game.
> I don't know the numbers for SDR, but for soundcards that delay jitter
> is usually in the couple 100µs range, Ie way lower than most people
> would notice. But this is only true if the OS reports the buffer sizes
> correctly. On Linux that means no pulseaudio as it is known to mess up
> the buffer reporting completely, to the point where it was off by 10's of
> ms.
>
> I don't know what the numbers under windows are, but as I have never heard
> of any problems there it might just work correctly out of the box.
>
> Those I know who do precsision timing with SDR usually use the timestamping
> facilities on the SDR hardware and process those timestamps within
> GnuRadio.
>
> Attila Kinali
> --
> Malek's Law:
> Any simple idea will be worded in the most complicated way.
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>



-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] WWV receivers?

[Nick Sayer via time-nuts]

No, no, no.

The single chip in this case is an AFSK decoder. You still have to have an 
ordinary HF AM radio.

> On Oct 29, 2016, at 11:21 AM, Chris Albertson  
> wrote:
> 
> Are you sure the single chip receiver is not itself an SDR?  Maybe using a 
> little 8-bit uP inside?  I don't know.
> 
> In any case the jitter on the SDR depends on the sample rate clock.  If you 
> use a decent audio interface the clocks are not bad.  A little 4-pin crystal 
> oscillator controls the sampling.   Compared to the propagation delay the 
> quality of that crystal is a not a big deal.   
> 
> On Fri, Oct 28, 2016 at 10:36 PM, Nick Sayer via time-nuts 
> > wrote:
> That single-chip version is going to have a *LOT* less (and less variable) 
> latency than an SDR.
> 
> > On Oct 27, 2016, at 12:20 AM, Poul-Henning Kamp  > > wrote:
> >
> > 
> > In message <5a002554-8d90-4c75-95da-21db45d61...@kfu.com 
> > >, Nick Sayer via time-
> > nuts writes:
> >
> >> If you’re in North America, a CHU receiver is a lot easier to make
> >> than WWV/WWVH. The CHU timecode is just BEL 103 AFSK at 300 baud -
> >> it was a one-chip solution 20 years ago when I made one in college.
> >
> > We have CPUs and sounds-cards these days...
> >
> > Also: The KiwiSDR is nearly perfect hardware, no matter which VLF/HF
> > station you want:  You can track GPS and four (possibly 8) VLF/HF
> > stations at the same time.
> >
> > --
> > Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
> > p...@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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> and follow the instructions there.
> 
> 
> 
> -- 
> 
> Chris Albertson
> Redondo Beach, California

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Re: [time-nuts] WWV receivers?

[Attila Kinali]

On Sat, 29 Oct 2016 09:35:25 -0700
jimlux  wrote:

> > Should not be too high. If Jeff Sherman's and Robert Jörden's paper[1]
> > is any indication, then the jitter should be dominated by the jitter
> > of the ADC and its reference oscillator. So sub-ps, order of 100fs jitter
> > should be possible with proper design. Long term drift is another issue
> > and I have not completely figured out what are the contributors there.
> > Temperature stabilizing for sure helps, but it doesn't seem to be the
> > only effect.
> 
> 
> Well, that's "jitter in the original samples" which can be very low, as 
> you describe. But I would interpret the original question as "jitter 
> *through* an SDR" which implies that we're looking at the timing of 
> output vs input.

Oh.. yes...The whole latency into the PC is a whole different game.
I don't know the numbers for SDR, but for soundcards that delay jitter
is usually in the couple 100µs range, Ie way lower than most people
would notice. But this is only true if the OS reports the buffer sizes
correctly. On Linux that means no pulseaudio as it is known to mess up
the buffer reporting completely, to the point where it was off by 10's of ms.

I don't know what the numbers under windows are, but as I have never heard
of any problems there it might just work correctly out of the box.

Those I know who do precsision timing with SDR usually use the timestamping
facilities on the SDR hardware and process those timestamps within GnuRadio.

Attila Kinali
-- 
Malek's Law:
Any simple idea will be worded in the most complicated way.
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Re: [time-nuts] WWV receivers?

[Chris Albertson]

Are you sure the single chip receiver is not itself an SDR?  Maybe using a
little 8-bit uP inside?  I don't know.

In any case the jitter on the SDR depends on the sample rate clock.  If you
use a decent audio interface the clocks are not bad.  A little 4-pin
crystal oscillator controls the sampling.   Compared to the propagation
delay the quality of that crystal is a not a big deal.

On Fri, Oct 28, 2016 at 10:36 PM, Nick Sayer via time-nuts <
time-nuts@febo.com> wrote:

> That single-chip version is going to have a *LOT* less (and less variable)
> latency than an SDR.
>
> > On Oct 27, 2016, at 12:20 AM, Poul-Henning Kamp 
> wrote:
> >
> > 
> > In message <5a002554-8d90-4c75-95da-21db45d61...@kfu.com>, Nick Sayer
> via time-
> > nuts writes:
> >
> >> If you’re in North America, a CHU receiver is a lot easier to make
> >> than WWV/WWVH. The CHU timecode is just BEL 103 AFSK at 300 baud -
> >> it was a one-chip solution 20 years ago when I made one in college.
> >
> > We have CPUs and sounds-cards these days...
> >
> > Also: The KiwiSDR is nearly perfect hardware, no matter which VLF/HF
> > station you want:  You can track GPS and four (possibly 8) VLF/HF
> > stations at the same time.
> >
> > --
> > Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
> > p...@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@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
> and follow the instructions there.
>



-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] WWV receivers?

[jimlux]

On 10/29/16 4:49 AM, Attila Kinali wrote:

On Fri, 28 Oct 2016 23:01:52 -0700
Hal Murray  wrote:


nsa...@kfu.com said:

That single-chip version is going to have a *LOT* less (and less variable)
latency than an SDR.


Latency isn't an issue as long as it is known so that you can correct for it.

Has anybody measured the jitter through SDR and/or tried to reduce it?  I'd
expect that even if you counted cycles and such there would still be jitter
from not being able to reproduce cache misses and interrupts.


Should not be too high. If Jeff Sherman's and Robert Jörden's paper[1]
is any indication, then the jitter should be dominated by the jitter
of the ADC and its reference oscillator. So sub-ps, order of 100fs jitter
should be possible with proper design. Long term drift is another issue
and I have not completely figured out what are the contributors there.
Temperature stabilizing for sure helps, but it doesn't seem to be the
only effect.



Well, that's "jitter in the original samples" which can be very low, as 
you describe. But I would interpret the original question as "jitter 
*through* an SDR" which implies that we're looking at the timing of 
output vs input.


Consider an SDR which receives a RF signal that's BPSK modulated, and 
puts out a stream of data bits on a wire (as opposed to dumping into a 
file or network connection)-  and you want to look at an eye diagram of 
the output.






Attila Kinali

[1] "Oscillator metrology with software defined radio",
by Jeff Sherman and Robert Jörden, 2016
http://dx.doi.org/10.1063/1.4950898
http://arxiv.org/abs/1605.03505




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Re: [time-nuts] WWV receivers?

[paul swed]

Good thread. Thanks for the clue on the kiwiSDR. I went to the sites and
lots of fun playing with the receivers. As an example hearing LORAN C in
the Asia region.
Certainly seems the receiver is pretty sensitive and capable. Went hunting
for various low frequency timing signals such as JJY and the submarine
crusher signals. All were heard.
I agree with Bobs comments that the signal at WWV range can be all over the
place and though seasonal effects can be a somewhat accounted for the
reality is, its still pretty random. The changes can occur slowly or
rapidly.
Regards
Paul
WB8TSL

On Sat, Oct 29, 2016 at 9:03 AM, Bob Camp  wrote:

> Hi
>
> Let’s see…. WWV (not WWVB) gets here via a variety of propagation
> mechanisms
> that vary over the day. According to NIST (who probably know :) that puts
> a random timing
> variation of ~1 ms on the signal. Since some modes get me a signal and
> others don’t, there
> is no real reason to assume it is random. It can easily be an offset that
> varies month to month.
>
> Net result, forget about the chip delays. The signal already has a bunch
> of built in variability
> that will swamp anything in the silicon.
>
> https://www.nist.gov/pml/time-and-frequency-division/nist-
> radio-broadcasts-frequently-asked-questions-faq
>
> Also in the same data is the fact that the “as transmitted” signal is good
> to 100 ns. That’s plenty good
> enough for the system as described. It also is a pretty modest number for
> a GPS timing module. One
> would guess that the number is a bit better than 100 ns (it is NIST after
> all). It also does not directly
> compare to the GPS number since there are UTC offset numbers there as
> well. Bottom line is that
> there inevitably *are* numbers like that buried in the system once you get
> past the 1 ms.
>
> Bob
>
> > On Oct 29, 2016, at 1:36 AM, Nick Sayer via time-nuts <
> time-nuts@febo.com> wrote:
> >
> > That single-chip version is going to have a *LOT* less (and less
> variable) latency than an SDR.
> >
> >> On Oct 27, 2016, at 12:20 AM, Poul-Henning Kamp 
> wrote:
> >>
> >> 
> >> In message <5a002554-8d90-4c75-95da-21db45d61...@kfu.com>, Nick Sayer
> via time-
> >> nuts writes:
> >>
> >>> If you’re in North America, a CHU receiver is a lot easier to make
> >>> than WWV/WWVH. The CHU timecode is just BEL 103 AFSK at 300 baud -
> >>> it was a one-chip solution 20 years ago when I made one in college.
> >>
> >> We have CPUs and sounds-cards these days...
> >>
> >> Also: The KiwiSDR is nearly perfect hardware, no matter which VLF/HF
> >> station you want:  You can track GPS and four (possibly 8) VLF/HF
> >> stations at the same time.
> >>
> >> --
> >> Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
> >> p...@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@febo.com
> > To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
> > and follow the instructions there.
>
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Re: [time-nuts] WWV receivers?

[Bob Camp]

Hi

Let’s see…. WWV (not WWVB) gets here via a variety of propagation mechanisms 
that vary over the day. According to NIST (who probably know :) that puts a 
random timing
variation of ~1 ms on the signal. Since some modes get me a signal and others 
don’t, there
is no real reason to assume it is random. It can easily be an offset that 
varies month to month. 

Net result, forget about the chip delays. The signal already has a bunch of 
built in variability
that will swamp anything in the silicon. 

https://www.nist.gov/pml/time-and-frequency-division/nist-radio-broadcasts-frequently-asked-questions-faq

Also in the same data is the fact that the “as transmitted” signal is good to 
100 ns. That’s plenty good
enough for the system as described. It also is a pretty modest number for a GPS 
timing module. One
would guess that the number is a bit better than 100 ns (it is NIST after all). 
It also does not directly
compare to the GPS number since there are UTC offset numbers there as well. 
Bottom line is that
there inevitably *are* numbers like that buried in the system once you get past 
the 1 ms. 

Bob

> On Oct 29, 2016, at 1:36 AM, Nick Sayer via time-nuts  
> wrote:
> 
> That single-chip version is going to have a *LOT* less (and less variable) 
> latency than an SDR.
> 
>> On Oct 27, 2016, at 12:20 AM, Poul-Henning Kamp  wrote:
>> 
>> 
>> In message <5a002554-8d90-4c75-95da-21db45d61...@kfu.com>, Nick Sayer via 
>> time-
>> nuts writes:
>> 
>>> If you’re in North America, a CHU receiver is a lot easier to make
>>> than WWV/WWVH. The CHU timecode is just BEL 103 AFSK at 300 baud -
>>> it was a one-chip solution 20 years ago when I made one in college.
>> 
>> We have CPUs and sounds-cards these days...
>> 
>> Also: The KiwiSDR is nearly perfect hardware, no matter which VLF/HF
>> station you want:  You can track GPS and four (possibly 8) VLF/HF
>> stations at the same time.
>> 
>> -- 
>> Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
>> p...@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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Re: [time-nuts] WWV receivers?

[Poul-Henning Kamp]

In message <20161029134952.e60a2182e1f53844ec50b...@kinali.ch>, Attila Kinali 
writes:

>> nsa...@kfu.com said:
>> > That single-chip version is going to have a *LOT* less (and less variable)
>> > latency than an SDR. 
>> 
>> Latency isn't an issue as long as it is known so that you can correct for it.
>> 
>> Has anybody measured the jitter through SDR and/or tried to reduce it?  I'd 
>> expect that even if you counted cycles and such there would still be jitter 
>> from not being able to reproduce cache misses and interrupts.
>
>Should not be too high.

It should be nonexistent.

The sensible way to do SDR-timing, is to capture a signal from the disciplined
oscillator with the ADC samples, so that their precise timing relationship is
firmly bolted down.


-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@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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Re: [time-nuts] WWV receivers?

[Attila Kinali]

On Fri, 28 Oct 2016 23:01:52 -0700
Hal Murray  wrote:

> nsa...@kfu.com said:
> > That single-chip version is going to have a *LOT* less (and less variable)
> > latency than an SDR. 
> 
> Latency isn't an issue as long as it is known so that you can correct for it.
> 
> Has anybody measured the jitter through SDR and/or tried to reduce it?  I'd 
> expect that even if you counted cycles and such there would still be jitter 
> from not being able to reproduce cache misses and interrupts.

Should not be too high. If Jeff Sherman's and Robert Jörden's paper[1]
is any indication, then the jitter should be dominated by the jitter
of the ADC and its reference oscillator. So sub-ps, order of 100fs jitter
should be possible with proper design. Long term drift is another issue
and I have not completely figured out what are the contributors there.
Temperature stabilizing for sure helps, but it doesn't seem to be the
only effect.


Attila Kinali

[1] "Oscillator metrology with software defined radio",
by Jeff Sherman and Robert Jörden, 2016
http://dx.doi.org/10.1063/1.4950898
http://arxiv.org/abs/1605.03505


-- 
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Re: [time-nuts] WWV receivers?

[Hal Murray]

nsa...@kfu.com said:
> That single-chip version is going to have a *LOT* less (and less variable)
> latency than an SDR. 

Latency isn't an issue as long as it is known so that you can correct for it.

Has anybody measured the jitter through SDR and/or tried to reduce it?  I'd 
expect that even if you counted cycles and such there would still be jitter 
from not being able to reproduce cache misses and interrupts.

-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] WWV receivers?

[Nick Sayer via time-nuts]

That single-chip version is going to have a *LOT* less (and less variable) 
latency than an SDR.

> On Oct 27, 2016, at 12:20 AM, Poul-Henning Kamp  wrote:
> 
> 
> In message <5a002554-8d90-4c75-95da-21db45d61...@kfu.com>, Nick Sayer via 
> time-
> nuts writes:
> 
>> If you’re in North America, a CHU receiver is a lot easier to make
>> than WWV/WWVH. The CHU timecode is just BEL 103 AFSK at 300 baud -
>> it was a one-chip solution 20 years ago when I made one in college.
> 
> We have CPUs and sounds-cards these days...
> 
> Also: The KiwiSDR is nearly perfect hardware, no matter which VLF/HF
> station you want:  You can track GPS and four (possibly 8) VLF/HF
> stations at the same time.
> 
> -- 
> Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
> p...@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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Re: [time-nuts] WWV receivers?

[Poul-Henning Kamp]

In message <5a002554-8d90-4c75-95da-21db45d61...@kfu.com>, Nick Sayer via time-
nuts writes:

>If you’re in North America, a CHU receiver is a lot easier to make
>than WWV/WWVH. The CHU timecode is just BEL 103 AFSK at 300 baud -
>it was a one-chip solution 20 years ago when I made one in college.

We have CPUs and sounds-cards these days...

Also: The KiwiSDR is nearly perfect hardware, no matter which VLF/HF
station you want:  You can track GPS and four (possibly 8) VLF/HF
stations at the same time.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@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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Re: [time-nuts] WWV receivers?

[Chris Albertson]

I started to set up a WWV based reference clock.   As for a receiver SDR is
the best way to go but I built a tunnel front end.  It is easy to do
because it needs to only work at ne specify frequency so you can use a
crystal filter with norrow bandwidth.  The SDR receiver did direct
conversion that sampled in quadrature using a stereo sound card type
interface.   I disagree that even the cheap sound cards are good enough.
Get one that does 24-bit sample because they have enough dynamic range so
they can still work without a human operator tuning a gain knob.

The part I did not do was to modify the NTP reference clock drivers to
accept audio feed from Jack Audio.  This would allow internal software to
route audio between applications and not have to use multiple sound cards
and analog cables which seems silly.

Other projects came up and I figure it the world ends and the Internet goes
dark and GPS fails I can still know what time it is by watching the sun set
over the ocean every day.

Actually I've disconnected the GPS from my NTP server and notice only a 5
millisecond error on average using just pool servers

On Wed, Oct 26, 2016 at 5:46 AM, Nick Sayer via time-nuts <
time-nuts@febo.com> wrote:

> If you’re in North America, a CHU receiver is a lot easier to make than
> WWV/WWVH. The CHU timecode is just BEL 103 AFSK at 300 baud - it was a
> one-chip solution 20 years ago when I made one in college. On the software
> side, you’ll want a serial line discipline kernel module of some sort that
> timestamps the incoming characters. The result is as good as HF radio will
> get you, which is to say probably 2 or 3 orders of magnitude minimum worse
> than GPS.
>
> IMHO the diversity of which you speak is exactly what NTP delivers. I
> believe NIST and USNO run NTP servers that aren’t sourced from GPS. Folks
> with Cesium clocks could conceivably do the same to provide independent
> standards.
>
> > On Oct 25, 2016, at 11:54 PM, Hal Murray 
> wrote:
> >
> >
> > tsho...@gmail.com said:
> >> I'm all for a diversity of systems - putting all our eggs in the GPS
> basket
> >> seems unwise (and I maintain WWV receivers hooked to NTP at home!)
> >
> > What is available in the way of WWV receivers?  Anybody got a summary
> handy?
> >
> >
> > --
> > These are my opinions.  I hate spam.
> >
> >
> >
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-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] WWV receivers?

[Nick Sayer via time-nuts]

If you’re in North America, a CHU receiver is a lot easier to make than 
WWV/WWVH. The CHU timecode is just BEL 103 AFSK at 300 baud - it was a one-chip 
solution 20 years ago when I made one in college. On the software side, you’ll 
want a serial line discipline kernel module of some sort that timestamps the 
incoming characters. The result is as good as HF radio will get you, which is 
to say probably 2 or 3 orders of magnitude minimum worse than GPS.

IMHO the diversity of which you speak is exactly what NTP delivers. I believe 
NIST and USNO run NTP servers that aren’t sourced from GPS. Folks with Cesium 
clocks could conceivably do the same to provide independent standards.

> On Oct 25, 2016, at 11:54 PM, Hal Murray  wrote:
> 
> 
> tsho...@gmail.com said:
>> I'm all for a diversity of systems - putting all our eggs in the GPS basket
>> seems unwise (and I maintain WWV receivers hooked to NTP at home!) 
> 
> What is available in the way of WWV receivers?  Anybody got a summary handy?
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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Re: [time-nuts] WWV receivers?

[Ruslan Nabioullin]

On 10/26/2016 02:54 AM, Hal Murray wrote:


tsho...@gmail.com said:

I'm all for a diversity of systems - putting all our eggs in the GPS basket
seems unwise (and I maintain WWV receivers hooked to NTP at home!)


What is available in the way of WWV receivers?  Anybody got a summary handy?


Yes, diversity is generally good, as it is in a sociological context. 
Despite being such a ubiquitous and critical system in all domains, 
military and civilian, US and foreign, and therefore being a recipient 
of extensive funding and R, it is a high-profile target to adversaries 
by means of anti-satellite weapons, cyberattacks, ground segment 
attacks, and jamming; additionally, the constellation is subject to the 
natural threats that all satellites face, and the system is controlled 
by a homogeneous structure of human entities, which reserve the right to 
deny coverage to a subset (typically hotspots in times of conflict).  It 
was a goal of my time metrology project, so I did do research in this 
area, expecting to use CHU (which also adds political diversity, for 
then it would be US [GPS] and Canada [CHU]) and maybe also WWV, but I 
abandoned the idea in favor of allocating the bulk of the budget to 
procurement of equipment and supporting equipment for my own house 
standard by means of a rubidium ensemble.


Yes, standalone WWV receivers of course do exist; if one wishes to go 
this route, the only practical means is by purchasing one of those 
ancient (late 70s era probably) Systron Donner time code generator units 
off eBay, which you'll notice has a BNC port on the back for an HF 
antenna (or just the audio feed---who knows?  Documentation is scarce). 
However, unless you need WWV-derived PPS, this approach is *greatly* 
suboptimal; the best approach would be to find your desired HF 
receiver(s) and connect them via sound card(s) to the NTP server(s), 
using the WWV module (and/or CHU).  Besides the unknowns resulting from 
documentation scarcity, this approach brings flexibility and the 
benefits of the ``less is more'' philosophy, for you gain: the freedom 
to decide what models of equipment to incorporate; flexibility in 
channels (you can also do CHU, and even within WWV you can do 2.5, 5, 
10, 15, and/or 20 MHz); and avoidance of obsolescence---remember, you're 
relying on some human entity's signal, who in this case of a 
seemingly-unpopular (at least nowadays) signal is under little 
obligation to preserve the characteristics and even presence of such a 
signal---look at what happened with the WWVB signal change, which 
effectively rendered what were once nice standard frequency WWVB 
receivers into paperweights.


For the radio, the best overall approach might be using $32 or so 
RTL-SDRs which feature a case.  However, the reception quality of these 
units is not so great, the DSP might overwhelm low-power and embedded 
servers, and there might be latency issues; I'm not familiar enough with 
SDRs to state for sure.  Another cheap approach is to simply use $12 or 
so, incl. shipping, handheld HF receivers, though from past experience 
the reception quality of them is absolutely awful and they are portable, 
consumer-grade devices, meaning that there's no antenna BNC port, there 
might be no power input apart from the terminals in the battery 
compartment, and there are no means of elegantly rack-mounting them.  A 
more costly approach is to use a general-purpose HF receiver (like 
typical Icom or Yaesu units that typical amateur radio operators use) or 
a professional HF receiver; unfortunately one is very limited in the 
latter, which consists of, in ascending order of price: HP 3586C (a 
measuring receiver actually), Ten-Tec (from the research I have done, is 
generally similar to Watkins Johnson [WJ], but lacks high-reliability 
specifications), and WJ.


For the sound card, it has been reported that those cheap Chinese USB 
sound cards, costing <$2 each incl. shipping, are adequate; I actually 
ordered a quantity-discounted lot of 5 or so of the popular variant 
which contains status LEDs before changing plans, so that's the best 
approach if you wish to use multiple sources or servers.


Note that for high-reliability setups, one must factor in potential 
service degradation caused by civil unrest or remote equipment failure, 
such as reduced station power output due to electricity shortages, loss 
of some channels, or jamming by adversaries.


-Ruslan
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[time-nuts] WWV receivers?

[Hal Murray]

tsho...@gmail.com said:
> I'm all for a diversity of systems - putting all our eggs in the GPS basket
> seems unwise (and I maintain WWV receivers hooked to NTP at home!) 

What is available in the way of WWV receivers?  Anybody got a summary handy?


-- 
These are my opinions.  I hate spam.



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