On Mon, August 13, 2018 9:16 pm, Chris Burford wrote:

A GPS disciplined oscillator contains a GPS receiver which outputs 1PPS
based on receiving the GPS signals and calculating the position  + time
equation. That PPS signal is noisy in time, it jitters around relative to
the ideal 1 second period.  The GPSDO implements a long time constant PLL
to synchronize the output of the OCXO to the long term average frequency
and phase of the GPS PPS, so what you see externally is 10MHz directly
from the OCXO, 1 Hz (PPS) which is divided down from the 10MHz OCXO, and
those are controlled by a PLL so that long term the phase of the PPS
divided down from the OCXO follows the PPS calculated by the GPS receiver,
but with lower jitter.

--
Chris Caudle

Don’t worry about how powerful the machines are. Worry about who the machines are giving  power to.

Sorry about the previous blank mail. Finger jitter.

As Chris points out the 1PPS from a GPSDO will « generally » be derived from the primary frequency and can show better performance than directly from a GPS receiver.
However this is becoming less and less true.
If you look at the Oscilloquarz blurb for the Star 4+ ( I found some here http://pdf.directindustry.com/pdf/oscilloquartz-sa/star3-4/62169-330779.html#search-en-oscilloquartz-star-4 ) , you will see that the phase stability (jitter) on the 1PPS output is +/- 30ns when locked to GPS, an it has a timing grade GPS receiver. This is not as good as other GPS modules now. 15ns is normal, with some less than half that.
The PRS10 has outstanding PLL control already. The SRS product doc gives +/- 10ns accuracy with +/-1ns resolution.
I don’t think that you are buying much with disciplining the PRS10 with a GPSDO 1PPS. Do you have any TIC measurements in this config to compare with a direct GPS 1PPS feed?

Don’t worry about how powerful the machines are. Worry about who the machines are giving  power to.

In message F1F265C0-DF79-469E-BB29-9B061F759392@sfr.fr, Mike Cook writes:

There is a large footnote about "hanging bridges" here.

If you feed the PRS10 from a GPS which produces "hanging bridges",
it will affect resultat PRS10 stability, as these bridges can be
quite long (any GPS) and tall (depending on model).

The 256 exponential average you can enable in the PRS10 is not a
good solution for this problem.

The best solution is if your GPS emits a "negative sawtooth correction"
and you grab that and feed it into the PRS10 and have it DTRT,
(provided its firmware is new enough).  That gets rid of some
of the "GPS-allan-ski-jump"

I would expect running the GPS through a GPSXO and into the PRS10
and selecting a correspondingly longer timesconstant in the PRS10
might also work, but I have not tried it.

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG        | TCP/IP since RFC 956
FreeBSD committer      | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

I forgot to mention one other thing which may be of interest to some. The 1PPS wave form output from the PRS10 is pretty mediocre. I put the details in another post here sometime back.
The Star4 spec is +/- 10ns, something I can only get from my PRS10s with a 74HC7001 shaper.

Don’t worry about how powerful the machines are. Worry about who the machines are giving  power to.

Hanging bridges out of a GPSDO's PPS? Interesting... time to try to
setup a measurement and see the relation between the GPS's PPS hanging
bridges and the corresponding DO's ones.
On Tue, Aug 14, 2018 at 9:55 AM Mike Cook michael.cook@sfr.fr wrote:

Could someone please define and explain the term 'hanging bridge' in this
context?

Thanks,

Dana

On Tue, Aug 14, 2018 at 7:02 AM, Azelio Boriani azelio.boriani@gmail.com
wrote:

On 8/14/18 12:29 AM, Mike Cook wrote:

I think the 1pps uncertainty spec for a receiver is more a function of
how they generate the 1pps - particularly if it's basically the period
of the internal clock.  A tight spec might just mean they've got a high
frequency clock.

The spec is probably also for a test condition where the GPS signals
into the receiver are perfect.  In real life, there's the ever changing
multipath, ionospheric scintillation, etc..

So I can imagine a receiver with very good performance on perfect
signals, but with poor "averaging", so that in a real signal
environment, the 1pps varies quite a lot on a pulse by pulse basis.
Likewise, I can imagine a receiver with a fairly large 1pps uncertainty
spec, but since the oscillator it is derived from is fairly stable and
high quality, over the long term, it tracks a 1pps more precisely  and
predictably (e.g. the receiver puts out offset/sawtooth correction data)

For a definition of hanging bridge in the GPS receiver's context see:

http://www.leapsecond.com/pages/m12/sawtooth.htm

On Tue, Aug 14, 2018 at 2:58 PM jimlux jimlux@earthlink.net wrote:

Hi

A normal GPS module generates it’s outputs off of a free running internal clock. Generally
this is a TCXO in a “timing” GPS ( = one that puts out a rational PPS).  This is a bit counter
intuitive, since you would think they phase lock the local source in the module. They don’t
mainly because it makes the math easier.

The gotcha with a free running clock is that the device can only generate an edge (like a pps)
when the clock edge(s) allow it to. For simplicity, lets just go with the rising edge and accept that
there could be double edge designs as well.  Let’s also assume a 25 MHz clock. That’s in the
general range of what shows up on the surplus GPSDO modules.

The internal fix math in the module comes up with a solution for “when should I send the PPS”.
The clock edges are 40 ns apart. The solution says that the “right time” is 10 ns after an edge.
The module sends out a PPS that is 10 ns early. Next second the math says that the right time
is 30 ns after an edge. The module sends out a PPS that is 10 ns late.

As long as it keeps going early / late / early /late things will average out. What makes it do this
is the local clock on the module being a bit off frequency (modulo 1 Hz). As the clock drifts around
(and they do) you may hit a region where it is relatively stable. It will then send out early /early /early….
( or late / late /late…..)

If the local clock is a TCXO, the “stable points” are likely to also be points of frequency reversal.
The net result is that the early / early /early never gets a corresponding late /late / late to average
against. It will pass right through a PLL and create an offset in the output.

I believe that NIST was the first to spot this and document it with lots of plots. I could be wrong about
that. It was pretty much ignored in the days before SA was turned off. The SA jitter masked out a lot
of issues. Most modern GPSDO’s use sawtooth correction messages to get around the problem. There
may be a few still in production that don’t.

Without full doc’s on a GPSDO, you really don’t know where the PPS is set to originate. It may
be coming from the disciplined clock on the board. It also may be coming straight from the GPS
module. There are indeed units out there that will let you do it either way under software control.

Bob

In message CADHrwpew_K=WJX58wdRGmjbANkjRNA5i2VSqnWSkOwC6-b0kGQ@mail.gmail.com, Dana Whitlow writes:

Look first at this illustrative plot from Toms site:

http://www.leapsecond.com/pages/m12/1phase8.gif

The situation is the following:

The gps receiver has a clock running at some frequency, lets say
30MHz in this case.

The gps receiver uses a programmable digital circuit to emit the
1PPS pulse as close to the point in time the GPS signals resolve
to, but it has to choose either clockcycle N or N+1, it cannot do
N+0.234.

The next 1PPS will be somewhere near N+30000000, then near N+60000000 etc.

Since the clock in the GPS is not perfectly on frequency, and because
it changes frequency due to temperature and all the other usual effects,
there will not be exactly 30000000 clock cycles between the 1PPS pulses
it generates, sometimes there will be 29999999 and sometimes there
will be 30000001.

That is what you see on Toms plot.

In this case, the GPS Xtal is really moving, so the hanging bridges
are only half a minute long.

Counter to anything you would expect, putting the GPS receiver in
a nice a stable temperature makes the problem worse, because the
hanging bridges get longer, I've seen them up to about 3000 seconds.

In that cae, for almost an hour, you get 1PPS signals that told
you that the frequency was 30ns/3000 seconds = 1e-11 wrong, and
then it suddenly steps 30 ns on you...

On good receiver the serial datastream contains a cure for this, a
field called "negative sawtooth correction" or something similarly
obscure, and it would look something like this around the "pillar"
of the bridge:

"The next 1PPS will be 14ns early"
"The next 1PPS will be 14ns early"
"The next 1PPS will be 15ns early"
"The next 1PPS will be 15ns late"
"The next 1PPS will be 15ns late"
"The next 1PPS will be 14ns late"
"The next 1PPS will be 14ns late"

Only if you measure the 1PPS, and apply this correction, then you get
the theoretical performance of your GPS, (subject to a 1ns/s jitter
from the resolution of the data field)

--
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.

Thanks Bob and Azello.  Now I understand the terminology and also better the
mechanism for the sawtooth error.

I once read that the LO, at least, in some GPS receivers, was not even
crystal
controlled but was rather a ring oscillator based on a string of cascaded
logic inverters on the chip.  This always sounded improbable to me, and i've
long wondered it this claim was really true.  Can either of you shed light
on
this issue?

Thanks,

Dana

On Tue, Aug 14, 2018 at 8:04 AM, Bob kb8tq kb8tq@n1k.org wrote:

Hi

I can think of no way to get the close in phase noise of a ring oscillator down far
enough to use it as the main clock for a GPS module. It is reasonable that the
L band LO in the module is a phase locked ring oscillator.,

Bob

Is there a need to make the math easier?
This is what we have microprocessors for.

Thanks for the "hanging bridge" explanation. It would be nice if
someone had a time-nuts-glossary that included various terms that
come up on the list, like "hanging bridge", "spurs", "sawtooth
correction", "GPS allan ski jump", etc.

Is there a time-nuts FAQ?

Hi

There is always a need to make the math easier if I’m quickly typing up an example. For proof I
reference the hundreds of posts in the archives where I didn’t quite get it right :)

Indeed, the real numbers could be just about anything. They are highly dependent on what’s in
the specific module. In some cases, the clock involved is well over 300 MHz.

Bob

In message 0C753B64-0C67-446F-B963-732B397A6E76@n1k.org, Bob kb8tq writes:

I may have been first there.  At least a Motorola person told me
that it was the curves I'd sent them that got NIST interested.

The curves in question were actually a bug-report:  The first version
their firmware announced the offset of the previous rather than the
next 1PPS flank.

--
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.

In message 20180814143354.GA29076@panix.com, Ron Bean writes:

Every so often somebody proposes a time-nuts wiki, then somebody
tries to read the manual page for the mediawiki software and
the idea dies again :-)

--
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.

On 8/14/18 8:13 AM, Poul-Henning Kamp wrote:

I feel that pain...

A straight up text file might not be a bad thing.  One can edit it with
anything, then.  Probably want to avoid modern character sets and stick
with ASCII.  We could spend some time away from the bikeshed (the
bristles are falling off the brush by now)  and discuss whether we want
line terminations as LF, CR, or CR LF or LF CR.

Hi Ron,

We've considered that several times. There are problems.

Also it's hard to beat the already superb NIST Time & Frequency FAQ / A-Z glossary. There's an index, or just start with A and read through several dozen webs pages until you get to Z:

https://www.nist.gov/time-and-frequency-services/am-b
...
https://www.nist.gov/time-and-frequency-services/x-z

That document works for almost all the words and concepts you're curious about. Really good for a newcomer to the world of time & frequency. Colloquial words like hanging bridge or TAPR-TICC, etc. are found in the time-nuts archives, which acts like a giant living FAQ. Or just ask. Additional information, as well as hints on searching the archives, is described on the time-nuts intro page:

http://leapsecond.com/time-nuts.htm

/tvb

Another question, a bit off the road of this thread:
Is there any common practice for the duty cycle of the 1 PPS pulse?
I have seen devices having extremely short 1 PPS pulses with duty cycles of a few percent or less and others with close to 50% duty cycle.

Best regards
Bernd
DK1AG

-----Ursprüngliche Nachricht-----
Von: time-nuts [mailto:time-nuts-bounces@lists.febo.com] Im Auftrag von Bob kb8tq
Gesendet: Dienstag, 14. August 2018 17:05
An: Discussion of precise time and frequency measurement time-nuts@lists.febo.com
Betreff: Re: [time-nuts] 1PPS for the beginner

Hi

There is always a need to make the math easier if I’m quickly typing up an example. For proof I reference the hundreds of posts in the archives where I didn’t quite get it right :)

Indeed, the real numbers could be just about anything. They are highly dependent on what’s in the specific module. In some cases, the clock involved is well over 300 MHz.

Bob

time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

With a scope it is super easy to look at PPS pulses that are microsecond to
a few milliseconds wide and tell you are triggering on the "leading edge".

Harder to decide at 50% duty cycle especially if you think it might have
been inverted along the way (almost all buffers are inverting).

Of course if you were 50% duty cycle you could figure out which edge was
which by listening to WWV. Oops not that topic again.

Tim N3QE

On Tue, Aug 14, 2018 at 2:52 PM, Bernd Neubig BNeubig@t-online.de wrote:

Bernd,

Typically all you want is the leading edge. So a 10 or 20 us wide pulse is enough for most purposes. The duty cycle is essentially zero in this case.

A noted exception is when the pulse is detected using vintage RS232 modem signal inputs, for example, when NTP uses DCD to catch a 1PPS. In that case a much wider pulse, many milliseconds, is required. See also FatPPS [1]. Modern computers which have GPIO don't have this problem since IOC interrupts or time capture registers will detect the leading edge and pulse width doesn't matter.

I used to like 1 Hz square waves. But over the years I've learned that having racks of gear exchanging 1PPS (5V into 50R) along with lots of flashing LEDs, all aligned to UTC, created noticeable periodic jumps in my 120 VIC mains, which invites injection locking.

/tvb

[1] https://www.tapr.org/kits_fatpps.html

----- Original Message -----
From: "Bernd Neubig" BNeubig@t-online.de
To: "'Discussion of precise time and frequency measurement'" time-nuts@lists.febo.com
Sent: Tuesday, August 14, 2018 11:52 AM
Subject: Re: [time-nuts] 1PPS for the beginner

On Tue, 14 Aug 2018 08:34:06 -0500
Dana Whitlow k8yumdoober@gmail.com wrote:

This wouldn't work. A simple ring oscillator is not stable enough
and has too much noise to demodulate the GPS signal successfully.
You need at least something of the class of an ceramic resonator
to come close to what you need for successful decoding of the GPS
signal. Most choose a XO simply because they are not much more
expensive and give quite a bit of boost in SNR. Timing GPS receivers
usually go for the TCXO because this allows for longer integration
times and thus higher SNR [1]. If you want to go for even longer
integration times, you have to go for OCXOs. There was a nice
master thesis by Pascal Olivier Gaggero 10 years ago on that topic[2].

What is true, though, is that a lot (most?) GPS receivers use a
ring oscillator as a local oscillator somewhere, either as RF LO source
or for the baseband processing. But this ring oscillator is always
locked to some XO/TCXO to improve its stability.

		Attila Kinali

[1] You can do longer integration times with normal XOs as well,
but then at some point the noise and (in)stability of the XO will
limit the maximum SNR you can get, which won't increase anymore
even if you increase the integration time.

[2] "Effect of oscillator instability on GNSS signal integration time",
by Pascal Olivier Gaggero, 2008
https://www.ucalgary.ca/engo_webdocs/other/PGaggero_Neuchatel_08.pdf

It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neal Stephenson

On Tue, 14 Aug 2018 20:52:50 +0200
"Bernd Neubig" BNeubig@t-online.de wrote:

As short as the consumer can take. Because a long pulse means that
you are wasting energy and heating up both the pulse generator
and the consumer. As TvB wrote, it varies from a few µs to a few ms.

		Attila Kinali

--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neal Stephenson

Arecibo did a kind of cute trick with their distributed 1PPS.  The one
second pulses were of one length
(100 ns as I recall), but the 10 sec boundaries had the pulses be about
twice that length.  One could carry
this scheme to considerable lengths as desired.

Dana

On Tue, Aug 14, 2018 at 4:00 PM, Attila Kinali attila@kinali.ch wrote:

On Tue, August 14, 2018 3:56 pm, ed breya wrote:

The Trimble Thunderbolt works that way.  A very good GPDSO.  You need
access to the GPS hardware and firmware at a very low level to make that
work, I don't think you can do that trick with off the shelf GPS hardware,
which I assume is why only Trimble has done it.

--
Chris Caudle

On Tue, 14 Aug 2018 11:05:17 -0400
Bob kb8tq kb8tq@n1k.org wrote:

I am pretty sure that the math is less the problem than being able
to control the oscillator precisely enough while staying at low cost.

The average TCVCXO has a tuning range of...let's say 10ppm = 1e-5
over a range of 0-3V. Now, we want to be able to shift the phase
such, that we are within 1ns at the next pulse (actually we want it
to be better, but lets keep the numbers simple). This means we need
to control the frequency with a precision of 1e-9. Hene we would need
a DAC resolution of 1e-4 or 14bit. That's already a DAC that has a price
tag, multiple times that of the TCXO. Hence it's cheaper just to
shift the frequency/phase digitally and not touch the TCXO.

		Attila Kinali

--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neal Stephenson

On Tue, 14 Aug 2018 13:56:40 -0700
ed breya eb@telight.com wrote:

Dithering is not as easy as it would seem at first. You still need to
relate the oscillators frequency and phase to the GPS signal. Which means
you have to use the dithered signal as frequency source at least for
the baseband processing. But using a dithered frequency source means
using a frequency source with a (very) bad phase noise. Which reduces
the SNR quite considerably.

		Attila Kinali

--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neal Stephenson

DAC that has a price

I'm not sure what you consider "low cost' but a 16 bit DAC like the
MAX5216BGUA+
https://www.mouser.com/ProductDetail/Maxim-Integrated/MAX5216BGUA%2b?qs=sGAEpiMZZMswix2y39ylddFcA27kRSR8c6%2fDlE45lrQ%3d
goes for $3.40, quantity one.

Wayne

On Tue, Aug 14, 2018 at 2:33 PM, Attila Kinali attila@kinali.ch wrote:

On Tue, 14 Aug 2018 14:42:52 -0700
Wayne Holder wayne.holder@gmail.com wrote:

If you want a product that ships on time, you dont buy Maxim ;-)

A 14bit DAC can be had for about 2USD at 1000pcs. A TCXO costs
in the order of 1USD at 1000pcs. A simple XO goes for less than 0.1$.

I guestimate that a GPS receiver like a u-blox LEA has a BOM cost
of less than 10$. Adding a 2$ component will seriously hurt the
ability of the CEO to buy a new Porsche with his next bonus. ;-)

		Attila Kinali

--
<JaberWorky> The bad part of Zurich is where the degenerates
throw DARK chocolate at you.

On 8/14/18 2:15 PM, Dana Whitlow wrote:

That's how IRIG works.. 3 different pulse lengths.

And you can come up with other schemes that are DC balanced, or constant
power (so TvB's line voltage fluctuations problem with all the lights
blinking together can be suppressed).

(which makes me wonder - wind farms have red warning beacons that blink
at the same time.. it looks very odd at night from a plane, if that's
all you see.. it's sort of like this spotted red curve that blinks on
and off in the distance - but does the blink rate show up in the output
of the wind farm? - I noticed it the first time flying into Burbank,
where you come in to the north, over Lancaster/Palmdale area.. there's
lots of wind turbines to the north by Tehachapi pass)

Dana,

One version of this would be to make the pulse width 100 ns * (1+STOD), where STOD (Seconds-Time-Of-Day) varies from 00000 to 86399. So your pulse width would vary from 100 ns to 8640000 ns = 8.64 ms. If 100 ns is too short use a range of, say, 1 us to 86400 us (86.4 ms). Maybe there's a reason no one has implemented this but I always thought it would be a cool self-clocking, self-identifying, IRIG-like format. And trivial to implement both the sender and receiver with a microcontroller

/tvb

On Tue, Aug 14, 2018 at 10:34 PM Tom Van Baak tvb@leapsecond.com wrote:

I wonder if the self clocking wouldn't be a bit tricky in that you'd
have to distinguish very close ratios, e.g. 86398/86399 vs
86397/86398. One downside of this scheme is that it requires handling
a range of 86400x in pulse size, not so good if you care about keeping
them short.  But this is wasteful because the seconds in a day come in
a predictable order.

I once needed to solve a non-timing related problem of recovering a
48-bit sequence number used for synchronizing a stream cipher with
receivers that could tune in at any time but could only spend 8-bits
per packet, I solved it using a de Bruijn sequence.

Applied here, you'd have two unambiguous pulse lengths and a 2^17 de
bruijn sequence. You send pulses based on your position in the
sequence. The receiver can unambiguously recover its position after
seeing 17 pulses due to the debruijn property.  Even short vs long can
be clocked from the sequence because every 17 pulses will have a least
one of each (except for the time a run of 17 ones or the time 17 zeros
come up, but since 2^17 > 86400 you can position this out of the
sequence that you're using).  17 might be more than you'd like, but it
can be made smaller by having more pulses to distinguish from...  so
you can get a trade-off between recovery time vs pulses that need to
be distinguished.

With this added flexibility it might be plausible to add additional
data like a small day number field, so even more devices can enjoy the
GPS wraparound problems. :P

Attila wrote:

While I agree with the sentiment, I imagine that time nuts who are
looking for solutions on-list are mostly hobbyists, not industrial
designers (who would almost certainly have a procurement system behind
them).  For quantities from 1 to 100 or 1000, a hobbyist will go to a
stocking distributor and will know exactly how many are available when
(s)he orders.

The lack of a second source for some Maxim products is another issue of
possible concern, but again, not so much for the hobbyist (or even a
small manufacturer).

I find that Digi-Key is generally well-stocked with a good variety of
Maxim parts.

Best regards,

Charles

Hi Bernd,

One reference to 20us 1PPS pulse length is the ICD-GPS-060, see figure 3-2, page 3-3 (pdf page 19)

https://www.navcen.uscg.gov/pdf/gps/ICD-GPS-060B.pdf

Group - Are there other standard documents defining duty-cycle, voltage levels, rise times etc?

MfG

 Björn 

I was astonished to see the pulse-width in the document defined from the
base of the (sharp-cornered!) edges, and not the mid-point - totally
impractical!  Near the top of the previous page it says: "If required for
testing purposes, the pulse width at the 50% level may be determined by
extrapolation."  Now OK, the very wide tolerance on the pulse-width makes
this all rather academic, but surely that spec wasn't written by an
engineer? :-)

 Peter

On 15 August 2018 at 05:03, Björn bg@lysator.liu.se wrote:

On Peter Vince's topic, does anybody in the group know what part of the
waveforms transmitted by WWV & WWVB mark the second boundaries?

I was once comparing the timing of PPS pulses from a GPS receiver with
WWV's ticks, and saw about 5 msec delay to the ticks (in south central
Texas).
Obviously propagation and my receiver's internal delays account for most
of that, but I never could decide which part of the audio waveform I should
be referencing.

For WWV, I feel that the best choice would be the central peak in the
response
of a matched filter designed around the tick waveform, but I bet "they" did
something entirely different.  Hence the question posed above.

Dana

On Wed, Aug 15, 2018 at 7:22 AM, Peter Vince petervince1952@gmail.com
wrote:

In message CAJqU6XP6ZOygUD0xyCZaVk90Hss=H9sMqHn+ZYFgLwtXPMkGcg@mail.gmail.com, Peter Vince writes:

Given that the output is not specified into a defined impedance,
termination or even cable-length, I don't think specifying the
mid-point would be any more practical.

--
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.

On Wed, Aug 15, 2018 at 8:40 AM Dana Whitlow k8yumdoober@gmail.com wrote:

the tick waveform. See
https://www.nist.gov/pml/time-and-frequency-division/time-services/wwv-and-wwvh-digital-time-code-and-broadcast-format

There is an interesting collection of papers and articles about WWV and
WWVH here
https://www.nist.gov/pml/time-and-frequency-division/time-services/wwvwwvh-station-library

--Jim Harman

It says into 50ohms. 10V into 50ohms are certainly archaic by today’s signal levels.

20us (+50%-20%) - 16us to 30us is indeed very wide.

The boss signing the document has dual Master of Science degrees... there were certainly engineers contributing to the document.

Are there any better standards around?

/Björn

On Tue, 14 Aug 2018 23:03:46 -0400
Charles Steinmetz csteinmetz@yandex.com wrote:

Sorry, that was a tongue-in-cheek comment. It wasn't ment seriously...
Especially considering that Maxim has a lot of very specialized
ICs that fill the needs left by the other, larger manufacturers.

		Attila Kinali

--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neal Stephenson

Wanted to add a bit to the conversation. At least in a number of older GPS
receivers circa 1989-1994 the LO was indeed locked to a 10 MHz reference.
These were the typical separate mixer and antenna systems. The first LO was
1500 MHz.
That is an expensive way to go so I can see why whats described here is
attractive to lowering costs.
Regards
Paul
WB8TSL

On Tue, Aug 14, 2018 at 6:14 PM, Attila Kinali attila@kinali.ch wrote:

On 8/15/18 2:20 PM, paul swed wrote:

Indeed -
one of the JPL GPS receivers has a 38.656 MHz clock used to latch the
output of 1 bit comparators, which makes L1 alias to 9.476 Mhz, L2 alias
to 9.392 and L5 to 16.770

Hard to get much cheaper. No microwave mixers.  Just bandpass filters,
broadband amps, and a comparator at the end.

Frequencies chosen so that even in worst case Doppler, the offset is on
the same side of zero.

Well thats a heck of a tidbit to learn.
I built up hack multipliers and such to get some of the old GPS receivers
going.
The best was austron 2001. I did retire it as it was really getting to be a
pain to operate.
You had to know what your doing. Not sure I like that. Neo's have spoiled
me.
What was interesting was that somehow it made its way up to the MIT flea.
Picked it up for the chassis.
No antenna and such.
Powered it up and dealt with alarms. The lat and long on the box was the
Aricebo observatory in PR.
Pretty interesting how it could have showed up in Boston.
Reagrds
Paul

On Wed, Aug 15, 2018 at 8:15 PM, jimlux jimlux@earthlink.net wrote:

Hi,

On 08/15/2018 06:03 AM, Björn wrote:

However, very few boxes does deliver 10 V amplitude PPS pulses. They may
be 20 us, but then as "TTL levels into 50 Ohm" meaning a peak of about
2,5 V as result of 50 Ohm source impedance and 50 Ohm load impedance
voltage dividing the driving 5 V.

The MIL-STD-188-115 also has the same specification on page 12.

There are a few more in that cluster. I have not bothered to pull them
all down. It relates to the PTTI Interface so I expect them to be similar.

I think ITU managed to put one in their standards (finally), I'll check
for it.

Cheers,
Magnus