Re: [time-nuts] 1PPS users?

[Bob Stewart]

Hi Scott,
I do understand the reasons that these users want this quality of output.  It's 
who these users are, what fields, industries, etc, that I didn't quite 
understand.
Bob -
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info

  From: Scott Stobbe 
 To: Bob Stewart ; Discussion of precise time and frequency 
measurement  
 Sent: Sunday, December 18, 2016 8:22 PM
 Subject: Re: [time-nuts] 1PPS users?
   
Part of the reason 1PPS needs to be so clean is because you are continuously 
integrating phase noise of the LO (hopefully an OCXO). While 10 uS is pretty 
trivial off a gps receiver. Without gps, 10 us over 24 hrs with a plane jane 
AT-cut crystal subject environmental dynamics becomes ludicrous. More than 
likely the short term stability of GPSDO is cleaner than it needs to be for 
many applications, but that is so holdover over an hour or day remains 
reasonable.
On Sun, Dec 18, 2016 at 6:16 PM, Bob Stewart  wrote:

One thing I've never really understood is who actually uses the high-quality 
1PPS output from a GPSDO.  I have spent a lot of time, effort, and money on 
developing my GPSDO without a whole of thought to the user base.  It was just a 
quest for the best result I could obtain with a particular technology.  The 
frequency standard users was a no brainer.  Everyone who wants a frequency 
standard eventually understands they need to get a GPSDO, or an Rb, or a Cs.  
And that's all I thought I had: a good frequency standard.  And then Tom 
prodded me a bit and showed me the shortcomings of what I was doing, and I did 
something about it.  So, if an NTP user can get his time fix directly from a 
noisy receiver, who actually needs a time-accurate, low jitter 1PPS pulse?
Bob - AE6RV
 - -- --
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/ GFS-GPSDOs/info
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[time-nuts] Lady Heather for homebrew GPSDO

[Mark Sims]

Heather can pretty much do that now.  It has the ability to do screen dumps to 
a file (or series of files) on a scheduled basis.   Heather doesn't do the 
"spit out an html file thing",  but I know of several people that have scripts 
on their machine that take the screen dump images and serve them up on the web. 
 That way they can format/process/display the images in their desired form.  
Heather can also dump log files on a scheduled basis and those can be read, 
processed, served, and displayed however one wants.




> If Mark is looking for a winter project, he can turn LH into this:

https://www.realhamradio.com/GPS_websites_list.htm

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Re: [time-nuts] Lady Heather for homebrew GPSDO

[Tom Van Baak]

Hi Jim,

> --The EFC value is given as an integer percent -100 to 100, so there is not
> enough resolution to really tell what the DAC is doing.

Sounds like you're using :DIAG:ROSC:EFC:REL? which gives percent.
Instead try :DIAG:ROSC:EFC:ABS? which gives absolute DAC value.

> -- It does not have the satellite position and C/N data that is reported in
> the NMEA GSV sentence, so LH can't make its nice satellite plots.

Use the SS column of :SYST:STAT? for this.

Remember before LH there was GPScon. See tons of information on the Z3801A at:

https://www.realhamradio.com/GPS_Frequency_Standard.htm

This random one has nice examples of what you can do given the data from SCPI:

https://www.realhamradio.com/z3801a-turning-point.htm

If Mark is looking for a winter project, he can turn LH into this:

https://www.realhamradio.com/GPS_websites_list.htm

/tvb
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[time-nuts] Lady Heather for homebrew GPSDO

[Mark Sims]

The Z3801A does have a request for getting/setting the DAC value as a absolute 
(hex) number.  Heather uses the percentage version of the message.  Neither 
format tells you what you really want to know...  the actual DAC voltage.  
There is nothing to prevent you from sending a DAC percentage with 10 digit 
resolution...

Heather gets the Z3801A satellite position/signal level info by requesting the 
"SYST:STAT?" message once a minute at xx:xx:33  and parsing out the values from 
the status screen (ugh... another reason the Z3801A was never intended to have 
a computer monitor and control it).   This takes the receiver 3 seconds to 
send.  During that time no time codes, etc come in and you can't request any 
other information.  At least the device has a (kludgy) way of getting the 
information... the Datum StarLoc II says all sats are at az/el 0,0 ... at least 
it does give a signal level.


-
> 
--The EFC value is given as an integer percent -100 to 100, so there is not
enough resolution to really tell what the DAC is doing.

-- It does not have the satellite position and C/N data that is reported in
the NMEA GSV sentence, so LH can't make its nice satellite plots.
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Re: [time-nuts] 1PPS users?

[Hal Murray]

preilley_...@comcast.net said:
> I would like to get better than the +-10 nS that the better receivers
> provide. 

A GPSDO generally avoids the sawtooth offset.


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] 1PPS users?

[Scott Stobbe]

Part of the reason 1PPS needs to be so clean is because you are
continuously integrating phase noise of the LO (hopefully an OCXO). While
10 uS is pretty trivial off a gps receiver. Without gps, 10 us over 24 hrs
with a plane jane AT-cut crystal subject environmental dynamics becomes
ludicrous. More than likely the short term stability of GPSDO is cleaner
than it needs to be for many applications, but that is so holdover over an
hour or day remains reasonable.

On Sun, Dec 18, 2016 at 6:16 PM, Bob Stewart  wrote:

> One thing I've never really understood is who actually uses the
> high-quality 1PPS output from a GPSDO.  I have spent a lot of time, effort,
> and money on developing my GPSDO without a whole of thought to the user
> base.  It was just a quest for the best result I could obtain with a
> particular technology.  The frequency standard users was a no brainer.
> Everyone who wants a frequency standard eventually understands they need to
> get a GPSDO, or an Rb, or a Cs.  And that's all I thought I had: a good
> frequency standard.  And then Tom prodded me a bit and showed me the
> shortcomings of what I was doing, and I did something about it.  So, if an
> NTP user can get his time fix directly from a noisy receiver, who actually
> needs a time-accurate, low jitter 1PPS pulse?
> Bob - AE6RV
>  -
> AE6RV.com
>
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
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Re: [time-nuts] Performance of TDC7200

[Li Ang]

Hi
Thanks for the info. The fpga baesed TDC is something I am interested in. 
However, I am a beginner of fpga programming. Maybe next year I will spend 
sometime study this project. VHDL is quite difficult for a C programmer :(.  


Regards
Li Ang
BI7LNQ
---Original---
From: "Attila Kinali"
Date: 2016/12/16 02:00:32
To: "Discussion of precise time and frequency measurement";
Subject: Re: [time-nuts] Performance of TDC7200


On Fri, 9 Dec 2016 21:29:34 +0800
"Li Ang" <379...@qq.com> wrote:

> I've done some tests with TDC7200 and TDC_GP22 few months 
> ago.(https://www.febo.com/pipermail/time-nuts/2016-May/098170.html)

Thanks for the report. It's interesting to see that the TDC7200 performs
slightly better than the GP22.

BTW: If you are using a large FPGA like the EP4CE22, then you might
want to consider using it directly as a TDC. You can fit four ring oscillator
based TDC easily and have more than enough space for your control logic
(we did a 4 TDC system with an NIOS2 core and some glue and still had
space spare).

The bin with is in the order of 22ps, with excursions up to 100ps.

The code we used was based on the tdc-core by CERN[1] and can be found
on my git server [2]. Special thanks to Florian Huemer who got it
working properly.


Attila Kinali

[1] http://www.ohwr.org/projects/tdc-core/wiki
[2] http://git.kinali.ch/attila/nios2_clocksync/tree/master/fpga/cores/tdc

-- 
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, Neil Stephenson
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Re: [time-nuts] Lady Heather for homebrew GPSDO

[Jim Harman]

On Sun, Dec 18, 2016 at 1:06 PM, Mark Sims  wrote:

> Binary or NMEA you need routines like send_msg_start,  send item (like
> integer, float, double), send_msg_end.  For received messages you need
> things like get_message,  get_item_from_message, etc.  The code to do that
> is not much more complicated for a binary protocol or an ASCII one like
> NMEA.
>

One factor that leads me to prefer NMEA is that my GPS already produces it,
so all I would have to do for the satellite, time, and other GPS data would
be to send the NMEA sentences from the GPS to the host port, no parsing and
reformatting required. In order to inject GPSDO data into this stream, I
would have to implement an NMEA multiplexer and construct the new
sentence(s) as you describe above.Of course I would still need an NMEA
parser in order to interpret commands from the host, but in the Arduino
world there is TinyGPS++, a very handy open source library for this.

I see that although the Z3801A's SCPI messages would be pretty easy to
implement, there are several inconvenient or limiting aspects to this
interface. (please correct me if I am wrong on these)

--It does not stream data the way NMEA does, so the host has to keep asking
for data.

--As has been mentioned earlier, most of the responses have no identifier,
so both ends have to be careful not to get out of sync.

--The EFC value is given as an integer percent -100 to 100, so there is not
enough resolution to really tell what the DAC is doing.

-- It does not have the satellite position and C/N data that is reported in
the NMEA GSV sentence, so LH can't make its nice satellite plots.

One thing I like about the Z3801A's format is the way the TCOD message
includes brief status and alarm information, so the data doesn't get
clogged with routine data but the host can tell when to request detailed
information.


-- 

--Jim Harman
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Re: [time-nuts] 1PPS users?

[Peter Reilley]

There was a discussion here a while ago about synchronizing radio 
telescopes that
were separated by some miles.   The 1PPS from GPS was suggested as a 
possibility.


I am working on a project to do location by triangulation that uses the 
1PPS signal.
I would like to get better than the +-10 nS that the better receivers 
provide.


Pete.


On 12/18/2016 6:16 PM, Bob Stewart wrote:

One thing I've never really understood is who actually uses the high-quality 
1PPS output from a GPSDO.  I have spent a lot of time, effort, and money on 
developing my GPSDO without a whole of thought to the user base.  It was just a 
quest for the best result I could obtain with a particular technology.  The 
frequency standard users was a no brainer.  Everyone who wants a frequency 
standard eventually understands they need to get a GPSDO, or an Rb, or a Cs.  
And that's all I thought I had: a good frequency standard.  And then Tom 
prodded me a bit and showed me the shortcomings of what I was doing, and I did 
something about it.  So, if an NTP user can get his time fix directly from a 
noisy receiver, who actually needs a time-accurate, low jitter 1PPS pulse?
Bob - AE6RV
  -
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info
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Re: [time-nuts] 1PPS users?

[John Ackermann N8UR]

For amateur use, PPS comparison requires less equipment and can be more 
accurate than trying to measure RF rates like 10 MHz.


When comparing two PPS signals, phase slips are very infrequent so you 
can observe drift rate over minutes/hours/days with an oscilloscope or 
simple time interval counter to get much better resolution than most 
frequency counters can provide.  (Of course, a GPS works as well for 
this as a GPSDO, albeit with more short term jitter.)


John

On 12/18/2016 08:33 PM, Bob Stewart wrote:

Hi Jim,
Thanks Jim,

So, what I'm seeing so far, assuming I'm interpreting it correctly, is big 
budget commercial and government applications, generally clustering around 
time-controlled multiplexing, as well as the niche that is the space industry.  
Then there's the hobbyist, such as Eric who wants to control a Fedchenko clock, 
or similar type of application, such as whatever sort of spread spectrum that 
ham radio may morph into, or perhaps the low S/N EME guys.  Any others?
Bob

   From: jimlux 
  To: time-nuts@febo.com
  Sent: Sunday, December 18, 2016 6:56 PM
  Subject: Re: [time-nuts] 1PPS users?

On 12/18/16 3:16 PM, Bob Stewart wrote:

One thing I've never really understood is who actually uses the high-quality 
1PPS output from a GPSDO.  I have spent a lot of time, effort, and money on 
developing my GPSDO without a whole of thought to the user base.  It was just a 
quest for the best result I could obtain with a particular technology.  The 
frequency standard users was a no brainer.  Everyone who wants a frequency 
standard eventually understands they need to get a GPSDO, or an Rb, or a Cs.  
And that's all I thought I had: a good frequency standard.  And then Tom 
prodded me a bit and showed me the shortcomings of what I was doing, and I did 
something about it.  So, if an NTP user can get his time fix directly from a 
noisy receiver, who actually needs a time-accurate, low jitter 1PPS pulse?


Anyone who needs to trigger events at a precise time or log the
occurrence of an event uses the 1 pps - the serial port (or other
interface) gives you the "at the tone the time will be" message, and the
edge of the 1pps is the "tone".


I've got several systems flying in space (or soon to fly in space) that
use the 1pps from GPS to calibrate their internal clocks and/or to
provide an absolute time reference (along with the aforesaid time message).

For example, one needs to have your carrier frequency within a certain
tolerance for communications with the ground stations: you can either
fly a precision oscillator with an oven (big, heavy, high power) or you
can measure a not-so-precision oscillator (small, cheap, low power)
against a 1pps, and adjust your frequency that way.

I grant you that this is really more like *building* a GPSDO than
*using* a GPSDO.

I've used the 1pps from a GPSDO as a common trigger to synchronize
timing and timestamping for separate systems.



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Re: [time-nuts] HP Z3801a piezo oscillator does work

[paul swed]

Bob
I think Mark was suggesting that. As I explained its a odd package.
Regards
Paul
WB8TSL

On Sun, Dec 18, 2016 at 7:13 PM, Bob Camp  wrote:

> Hi
>
> Can you pull the crystal? sure.
>
> Does your MV-89 have a 5 MHz crystal (the frequency doubled version) or a
> 10 MHz crystal? (sub harmonics viewed on a
> spectrum analyzer are a really good way to tell).
>
> Is the crystal the same size / pinout? Probably not. HP used an odd
> package. You might be able to make a spacer.
>
> Will it hit the right frequency? Likely not without changing some parts ….
>
> Bob
>
>
> > On Dec 18, 2016, at 5:55 PM, Mark Sims  wrote:
> >
> > I have a wonky Morian MV-89... probably the well know output cap
> failure.   I wonder if one could pull the crystal out of that and stick in
> the HP10811?  Something tells me Bob would know  ;-)
> > ___
> > time-nuts mailing list -- time-nuts@febo.com
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Re: [time-nuts] 1PPS users?

[Bob Stewart]

Hi Jim,
Thanks Jim,

So, what I'm seeing so far, assuming I'm interpreting it correctly, is big 
budget commercial and government applications, generally clustering around 
time-controlled multiplexing, as well as the niche that is the space industry.  
Then there's the hobbyist, such as Eric who wants to control a Fedchenko clock, 
or similar type of application, such as whatever sort of spread spectrum that 
ham radio may morph into, or perhaps the low S/N EME guys.  Any others?
Bob

  From: jimlux 
 To: time-nuts@febo.com 
 Sent: Sunday, December 18, 2016 6:56 PM
 Subject: Re: [time-nuts] 1PPS users?
   
On 12/18/16 3:16 PM, Bob Stewart wrote:
> One thing I've never really understood is who actually uses the high-quality 
> 1PPS output from a GPSDO.  I have spent a lot of time, effort, and money on 
> developing my GPSDO without a whole of thought to the user base.  It was just 
> a quest for the best result I could obtain with a particular technology.  The 
> frequency standard users was a no brainer.  Everyone who wants a frequency 
> standard eventually understands they need to get a GPSDO, or an Rb, or a Cs.  
> And that's all I thought I had: a good frequency standard.  And then Tom 
> prodded me a bit and showed me the shortcomings of what I was doing, and I 
> did something about it.  So, if an NTP user can get his time fix directly 
> from a noisy receiver, who actually needs a time-accurate, low jitter 1PPS 
> pulse?

Anyone who needs to trigger events at a precise time or log the 
occurrence of an event uses the 1 pps - the serial port (or other 
interface) gives you the "at the tone the time will be" message, and the 
edge of the 1pps is the "tone".


I've got several systems flying in space (or soon to fly in space) that 
use the 1pps from GPS to calibrate their internal clocks and/or to 
provide an absolute time reference (along with the aforesaid time message).

For example, one needs to have your carrier frequency within a certain 
tolerance for communications with the ground stations: you can either 
fly a precision oscillator with an oven (big, heavy, high power) or you 
can measure a not-so-precision oscillator (small, cheap, low power) 
against a 1pps, and adjust your frequency that way.

I grant you that this is really more like *building* a GPSDO than 
*using* a GPSDO.

I've used the 1pps from a GPSDO as a common trigger to synchronize 
timing and timestamping for separate systems.



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Re: [time-nuts] Why is holdover LED on HP 58503A not lit, when GPS lock is unlit too?

[Hal Murray]

drkir...@kirkbymicrowave.co.uk said:
> I assume it wont start until it has tracked sufficient number of satellites.

There is a chicken-egg problem with getting started.  The satellites tell you 
where they are, but you need to know where they are and where you are in 
order to calculate the Doppler offset so you know what frequency to listen to.

The difference between warm start and cold start is that for a warm start the 
receiver has a 32KHz clock and has saved its last position and the satellite 
orbit data in battery backed RAM.

-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] 1PPS users?

[Chris Albertson]

Who uses 1PPS?  In industry they are used to phase lock various
oscillators.   I would bet most of those oscillators are used in the
telecommunications industry both for bit rate clocks and for carrier
frequency synthesis.

We also see a lot of 1 PPS used for NTP servers that in turn are used to
keep computer internal time of day clocks running at the correct rate.



On Sun, Dec 18, 2016 at 3:16 PM, Bob Stewart  wrote:

> One thing I've never really understood is who actually uses the
> high-quality 1PPS output from a GPSDO.  I have spent a lot of time, effort,
> and money on developing my GPSDO without a whole of thought to the user
> base.  It was just a quest for the best result I could obtain with a
> particular technology.  The frequency standard users was a no brainer.
> Everyone who wants a frequency standard eventually understands they need to
> get a GPSDO, or an Rb, or a Cs.  And that's all I thought I had: a good
> frequency standard.  And then Tom prodded me a bit and showed me the
> shortcomings of what I was doing, and I did something about it.  So, if an
> NTP user can get his time fix directly from a noisy receiver, who actually
> needs a time-accurate, low jitter 1PPS pulse?
> Bob - AE6RV
>  -
> AE6RV.com
>
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
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-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] HP Z3801a piezo oscillator does work

[Bob Camp]

Hi

Can you pull the crystal? sure. 

Does your MV-89 have a 5 MHz crystal (the frequency doubled version) or a 10 
MHz crystal? (sub harmonics viewed on a
spectrum analyzer are a really good way to tell). 

Is the crystal the same size / pinout? Probably not. HP used an odd package. 
You might be able to make a spacer. 

Will it hit the right frequency? Likely not without changing some parts ….

Bob


> On Dec 18, 2016, at 5:55 PM, Mark Sims  wrote:
> 
> I have a wonky Morian MV-89... probably the well know output cap failure.   I 
> wonder if one could pull the crystal out of that and stick in the HP10811?  
> Something tells me Bob would know  ;-)
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Re: [time-nuts] HP Z3801a piezo oscillator does work

[paul swed]

Mark
I tend to agree with you on Bob. But that said the 10811 crystal is a bit
odd.
Its actually a copper cylinder with a screw on top. I believe to insure
correct even heat distribution. There are pix's of it on one of the sights.
Maybe the crystal comes out of the copper.
The 10811 used in the Z3801 is a bit different from standard 10811 in the
tuning sensitivity and I may believe that stability of the steps. But thats
a guess. Some of the sites mention this.
My goal was to simply confirm the rest of the 3801 boards were good and it
is. So I have a spare for my operating 3801. Though it seems to be doing a
fair job as compared to a TBolt I am using as a reference.

I have messed with the bad 10811 checking caps, resitors, and temperature
and its still 50 Hz low. May dive back into that though I have exhausted
pretty much anything thats possible.

Need to clean things up by a lot. Then go searching for the com ports
stalls that sort of started this journey.
Regards
Paul
WB8TSL

On Sun, Dec 18, 2016 at 5:55 PM, Mark Sims  wrote:

> I have a wonky Morian MV-89... probably the well know output cap failure.
>  I wonder if one could pull the crystal out of that and stick in the
> HP10811?  Something tells me Bob would know  ;-)
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Re: [time-nuts] 1PPS users?

[Eric Scace]

Speaking as an owner of a well-behaved mechanical clock:
Clock rate performance over time can be done based on time interval 
measurements anchored to a solid frequency standard. No 1pps needed per se.
Bring a clock to time is simplified with a timescale-accurate 1pps source.

> On 2016 Dec 18, at 18:16 , Bob Stewart  wrote:
> 
> One thing I've never really understood is who actually uses the high-quality 
> 1PPS output from a GPSDO.  I have spent a lot of time, effort, and money on 
> developing my GPSDO without a whole of thought to the user base.  It was just 
> a quest for the best result I could obtain with a particular technology.  The 
> frequency standard users was a no brainer.  Everyone who wants a frequency 
> standard eventually understands they need to get a GPSDO, or an Rb, or a Cs.  
> And that's all I thought I had: a good frequency standard.  And then Tom 
> prodded me a bit and showed me the shortcomings of what I was doing, and I 
> did something about it.  So, if an NTP user can get his time fix directly 
> from a noisy receiver, who actually needs a time-accurate, low jitter 1PPS 
> pulse?
> Bob - AE6RV

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Re: [time-nuts] 1PPS users?

[Bob Camp]

Hi

Roughly 99% of all GPSDO’s are only used for the PPS output. They go into cell 
sites and the reason
they exist is to sync up the Gold Codes on CDMA. That’s also why you see a 
*lot* of PPS only Rb’s
on the surplus market. The ones that don’t get used for cell towers, mostly go 
into other com systems 
that for some reason need to have accurate time (also involves codes …).

Bob

> On Dec 18, 2016, at 6:16 PM, Bob Stewart  wrote:
> 
> One thing I've never really understood is who actually uses the high-quality 
> 1PPS output from a GPSDO.  I have spent a lot of time, effort, and money on 
> developing my GPSDO without a whole of thought to the user base.  It was just 
> a quest for the best result I could obtain with a particular technology.  The 
> frequency standard users was a no brainer.  Everyone who wants a frequency 
> standard eventually understands they need to get a GPSDO, or an Rb, or a Cs.  
> And that's all I thought I had: a good frequency standard.  And then Tom 
> prodded me a bit and showed me the shortcomings of what I was doing, and I 
> did something about it.  So, if an NTP user can get his time fix directly 
> from a noisy receiver, who actually needs a time-accurate, low jitter 1PPS 
> pulse?
> Bob - AE6RV
>  -
> AE6RV.com
> 
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
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Re: [time-nuts] 1PPS users?

[jimlux]

On 12/18/16 3:16 PM, Bob Stewart wrote:

One thing I've never really understood is who actually uses the high-quality 
1PPS output from a GPSDO.  I have spent a lot of time, effort, and money on 
developing my GPSDO without a whole of thought to the user base.  It was just a 
quest for the best result I could obtain with a particular technology.  The 
frequency standard users was a no brainer.  Everyone who wants a frequency 
standard eventually understands they need to get a GPSDO, or an Rb, or a Cs.  
And that's all I thought I had: a good frequency standard.  And then Tom 
prodded me a bit and showed me the shortcomings of what I was doing, and I did 
something about it.  So, if an NTP user can get his time fix directly from a 
noisy receiver, who actually needs a time-accurate, low jitter 1PPS pulse?


Anyone who needs to trigger events at a precise time or log the 
occurrence of an event uses the 1 pps - the serial port (or other 
interface) gives you the "at the tone the time will be" message, and the 
edge of the 1pps is the "tone".



I've got several systems flying in space (or soon to fly in space) that 
use the 1pps from GPS to calibrate their internal clocks and/or to 
provide an absolute time reference (along with the aforesaid time message).


For example, one needs to have your carrier frequency within a certain 
tolerance for communications with the ground stations: you can either 
fly a precision oscillator with an oven (big, heavy, high power) or you 
can measure a not-so-precision oscillator (small, cheap, low power) 
against a 1pps, and adjust your frequency that way.


I grant you that this is really more like *building* a GPSDO than 
*using* a GPSDO.


I've used the 1pps from a GPSDO as a common trigger to synchronize 
timing and timestamping for separate systems.




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Re: [time-nuts] 1PPS users?

[Hal Murray]

b...@evoria.net said:
> So, if an NTP user can get his time fix directly from a noisy receiver, who
> actually needs a time-accurate, low jitter 1PPS pulse?

Most kernels have an option to capture a time stamp from a PPS signal at 
interrupt time.  That is much more accurate than the timing you get from user 
mode on a serial data stream.

There is also a mode where the whole NTP PLL processing is done in the 
kernel.  I don't see why that should make as much of a difference as it does, 
but I haven't tracked down the details.  (It's not in the typical Linux 
kernel.  You have to build your own.)


Most low cost GPS receivers have crappy timing on the serial port.  Really 
crappy.  It wanders with a time scale of hours so you can't filter out the 
jitter by averaging for a minute or two.  PPS on that sort of unit makes it 
much more interesting.


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Why is holdover LED on HP 58503A not lit, when GPS lock is unlit too?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

It is looking much better now. I

1) Powered off
2) Left off for 30 s
3) Pulled antenna out.
4) Powered on
5) Connected antenna, making sure if was firmly screwed in.

It then got GPS lock in a few minutes. It is running at reduced accuracy,
with the survey only 9.7% complete, but it is looking more hopeful.

I can't help feeling there should have been more informative status
available by the LEDs. The fact it is locked, but at reduced accuracy,
should really be visable from the front panel IMHO. Anyway, it seems to be
getting there - see below.

scpi >  SYSTEM:STATUS?
--- Receiver Status
---

SYNCHRONIZATION  [ Outputs Valid/Reduced
Accuracy ]
SmartClock Mode ___   Reference Outputs
___
>> Locked to GPS: stabilizing frequency   TFOM 3
FFOM 1
   Recovery   1PPS TI -15.9 ns relative to
GPS
   Holdover   HOLD THR 1.000 us
   Power-up   Holdover Uncertainty

  Predict  432.0 us/initial 24
hrs

ACQUISITION  [ GPS 1PPS
Valid ]
Tracking: 6    Not Tracking: 3    Time _ +1 leap second
pending
PRN  El  Az   SS   PRN  El  AzUTC  22:39:23 18 Dec
2016
  2  28  87   86 6  20  48GPS 1PPS Synchronized to UTC
 12  57  70  11924  24 137ANT DLY  0 ns
 14  39 287  10631  27 303Position

 25  76 284   96  MODE Survey:9.7%
complete
 29  37 194   79
 32  39 249  109  AVG LAT  N  51:39:04.205
  AVG LON  E   0:46:36.347
ELEV MASK 10 deg  AVG HGT   +42.42 m
(MSL)
HEALTH MONITOR . [
OK ]
Self Test: OKInt Pwr: OK   Oven Pwr: OK   OCXO: OK   EFC: OK   GPS Rcv:
OK
scpi >
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Re: [time-nuts] Why is holdover LED on HP 58503A not lit, when GPS lock is unlit too?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 18 December 2016 at 18:19, Dan Rae  wrote:

> On 12/18/2016 9:34 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
>
>> 
>> *12  -- ---MODE Survey:  0%
>> complete
>>
>>
> If it's still showing that after being on for five hours, maybe it needs
> to be explicitly told to start a survey?
>
> dr
>


I seem to be having some issues now with this. I've reset it, and entered
the approximate latitude, longitude, height, as well as date and time. The
commands below were executed, although NOT necessarily in the order give.


E-113> GPS:INIT:DATe 2016,12,18
E-113> gps:init:time 19,18,35
E-113> SYSTEM:PRESET
scpi > DIAG:LOG:READ:ALL?
Log status: 2   entries

Log 001:19970504.00:00:00:  Log cleared
Log 002:19970504.00:00:00:  System preset

The receiver seems to find satellites fairly quickly, tries to track them,
and is showing reasonable values for the things I set, like date, time,
position etc. However,  the receiver doesn't seem able to track any
satellites, so not surprisingly the survey never starts. I assume it wont
start until it has tracked sufficient number of satellites.

scpi > SYSTEM:STATUS?
--- Receiver Status
---

SYNCHRONIZATION ... [ Outputs
Invalid ]
SmartClock Mode ___   Reference Outputs
___
   Locked TFOM 9
FFOM 3
   Recovery   1PPS TI  --
   Holdover   HOLD THR 1.000 us
>> Power-up: GPS acquisition  Holdover Uncertainty

  Predict  --

ACQUISITION .. [ GPS 1PPS
Invalid ]
Tracking: 0    Not Tracking: 12 ___   Time

   PRN  El  Az  PRN  El  Az   UTC  21:57:41 [?] 18 Dec
2016
 6  20  67   12  76  56   GPS 1PPS Invalid: not tracking
   * 7  -- ---   14  32 307   ANT DLY  0 ns
   * 8  -- ---   24  42 129   Position

   * 9  -- ---   25  58 259   MODE Survey:  0%
complete
   *10  -- ---  *31  10 299Suspended: track <4
sats
   *11  -- ---   32  45 274   INIT LAT N  51:39:03.825
  INIT LON E   0:46:36.277
ELEV MASK 10 deg   *attempting to track   INIT HGT  +29.99 m
(MSL)
HEALTH MONITOR . [
OK ]
Self Test: OKInt Pwr: OK   Oven Pwr: OK   OCXO: OK   EFC: OK   GPS Rcv:
OK


It will run overnight. Perhaps tomorrow it will sort itself out, but I'm
not too hopeful.


Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
UK.
Registered in England and Wales, company number 08914892.
http://www.kirkbymicrowave.co.uk/
Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)
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[time-nuts] 1PPS users?

[Bob Stewart]

One thing I've never really understood is who actually uses the high-quality 
1PPS output from a GPSDO.  I have spent a lot of time, effort, and money on 
developing my GPSDO without a whole of thought to the user base.  It was just a 
quest for the best result I could obtain with a particular technology.  The 
frequency standard users was a no brainer.  Everyone who wants a frequency 
standard eventually understands they need to get a GPSDO, or an Rb, or a Cs.  
And that's all I thought I had: a good frequency standard.  And then Tom 
prodded me a bit and showed me the shortcomings of what I was doing, and I did 
something about it.  So, if an NTP user can get his time fix directly from a 
noisy receiver, who actually needs a time-accurate, low jitter 1PPS pulse?
Bob - AE6RV
 -
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info
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[time-nuts] HP Z3801a piezo oscillator does work

[Mark Sims]

I have a wonky Morian MV-89... probably the well know output cap failure.   I 
wonder if one could pull the crystal out of that and stick in the HP10811?  
Something tells me Bob would know  ;-)
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[time-nuts] HP Z3801a piezo oscillator does work

[paul swed]

OK the 10 MHz Piezo oscillator from a lucent RC/xtal pair does work and the
3801 is doing what it should.

Some insights as mentioned. 3801 DAC being full scale is not an issue when
a good signal within 2 HZ is used it will come out of limit.

The DAC output was driving the piezo far to widely I added a 10:1 V
antennuator to reduce the swing. The piezo requires a positive only EFC and
its control is inverted as compared to the HP 10811. Used a single TL071
opamp to invert the signal and apply the offset. By calculations it should
have been offset to 3.6V but the system seems to want 2.5V. Pretty sure an
adjustment on the actual oscillator would fix that.

I can now see that something like an RB could be plugged into the 3801 etc.

But more important the proof is that the actual Z3801 is fully functional
and the only bad thing is a the HP 10811 oscillator.
Its been a great learning exercise. How to get rid of teh outer oven. How
to use far simpler power supplies to run the 3801 instead of the 48 volt
mess.
Overall a lower power consumption solution can be built.
Regards
Paul
WB8TSL
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[time-nuts] Lady Heather for homebrew GPSDO

[Mark Sims]

If you go digging in the Ladt Heather code, you will find references to a 
"luxor" device.  This is a LED / power analyzer device that I built.  It runs 
on a ATMEGA 2561 and uses the TSIP protocol.  I've also implemented the same 
TSIP protocol code on a '328 with 32kB of program memory.  It's not that hard 
to do.  At the lowest level it doesn't take much more code than a NMEA 
processor.  The code sends and receives properly formatted TSIP sentences.  
What gets really fiddly is all the details of trying to faithfully emulate an 
existing GPSDO.

Binary or NMEA you need routines like send_msg_start,  send item (like integer, 
float, double), send_msg_end.  For received messages you need things like 
get_message,  get_item_from_message, etc.  The code to do that is not much more 
complicated for a binary protocol or an ASCII one like NMEA.

Binary messages have the little complication of what byte ordering does the CPU 
and protocol use.  Heather has a find_endian routine that determines the CPU 
ordering for getting values from the received messages and re-ordering the 
bytes to what the CPU expects and the output routines reformat CPU values into 
the byte order that the receiver wants. 



>  Writing and *debugging* a binary protocol is a lot more involved than a 
> serial stream. You
can argue that code it code and it’s all trivial. 
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Re: [time-nuts] Why is holdover LED on HP 58503A not lit, when GPS lock is unlit too?

[Dan Rae]

On 12/18/2016 9:34 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:


*12  -- ---MODE Survey:  0%
complete

If it's still showing that after being on for five hours, maybe it needs 
to be explicitly told to start a survey?


dr
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Re: [time-nuts] Why is holdover LED on HP 58503A not lit, when GPS lock is unlit too?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 18 December 2016 at 14:31, Tim Shoppa  wrote:

> A common misconception, is that holdover is the opposite of GPS lock.
> Sometimes we might even talk about the two as if we're in one or the other.
> But really the power-on state, is that we're in neither holdover or GPS
> lock.
>
> Holdover means the smartclock previously had GPS lock and had used it to
> characterize the aging of the OCXO, and is maintaining the EFC
> extrapolation, such that it believes it can still produce accurate time and
> frequency through the GPS loss.
>
> The state of your clock at the moment, is that it has never had GPS lock
> since regaining power, it does not know what time it is, and it has not
> characterized or extrapolated the aging of the OCXO. So it is definitely
> not in holdover.
>
> Tim N3QE
>

Cheers Tim, that makes sense.

I'm a bit concerned it has not managed to track a single satellite, despite
it has been on 5 hours or so. But perhaps things have improved, as its not
attempting to track 6 (PRN=15, 2, 21, 25, 26 and 28), whereas before it was
attempting to track just with a PRN of 32. I'm hoping its current status
(see below), is looking more hopeful than what it was before.

scpi >
scpi > SYSTEM:STATUS?
--- Receiver Status
---

SYNCHRONIZATION ... [ Outputs
Invalid ]
SmartClock Mode ___   Reference Outputs
___
   Locked TFOM 9
FFOM 3
   Recovery   1PPS TI  --
   Holdover   HOLD THR 1.000 us
>> Power-up: GPS acquisition  Holdover Uncertainty

  Predict  --

ACQUISITION .. [ GPS 1PPS
Invalid ]
Tracking: 0    Not Tracking: 6    Time _ +1 leap second
pending
   PRN  El  AzUTC  14:43:22 [?] 01 Jan
1998
   *15  -- ---GPS 1PPS Invalid: not tracking
   *20  -- ---ANT DLY  0 ns
   *21  -- ---Position

   *25  -- ---MODE Survey:  0%
complete
   *26  -- --- Suspended: track <4
sats
   *28  -- ---INIT LAT N  51:39:03.825
  INIT LON E   0:46:36.278
ELEV MASK 10 deg   *attempting to track   INIT HGT  -14.04 m
(MSL)
HEALTH MONITOR . [
OK ]
Self Test: OKInt Pwr: OK   Oven Pwr: OK   OCXO: OK   EFC: OK   GPS Rcv:
OK
scpi > SYSTEM:STATUS?
--- Receiver Status
---

SYNCHRONIZATION ... [ Outputs
Invalid ]
SmartClock Mode ___   Reference Outputs
___
   Locked TFOM 9
FFOM 3
   Recovery   1PPS TI  --
   Holdover   HOLD THR 1.000 us
>> Power-up: GPS acquisition  Holdover Uncertainty

  Predict  --

ACQUISITION .. [ GPS 1PPS
Invalid ]
Tracking: 0    Not Tracking: 6    Time _ +1 leap second
pending
   PRN  El  AzUTC  16:59:08 [?] 01 Jan
1998
   * 8  -- ---GPS 1PPS Invalid: not tracking
   *10  -- ---ANT DLY  0 ns
   *11  -- ---Position

   *12  -- ---MODE Survey:  0%
complete
   *13  -- --- Suspended: track <4
sats
   *30  -- ---INIT LAT N  51:39:03.825
  INIT LON E   0:46:36.278
ELEV MASK 10 deg   *attempting to track   INIT HGT  -14.04 m
(MSL)
HEALTH MONITOR . [
OK ]
Self Test: OKInt Pwr: OK   Oven Pwr: OK   OCXO: OK   EFC: OK   GPS Rcv:
OK
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Re: [time-nuts] Why is holdover LED on HP 58503A not lit, when GPS lock is unlit too?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 18 December 2016 at 17:34, Dr. David Kirkby (Kirkby Microwave Ltd) <
drkir...@kirkbymicrowave.co.uk> wrote:

> But perhaps things have improved, as its not attempting to track 6
> (PRN=15, 2, 21, 25, 26 and 28), whereas before it was attempting to track
> just with a PRN of 32. I'm hoping its current status (see below), is
> looking more hopeful than what it was before.
>

I mean it is NOW attempting to track 6 !!! Almost the opposite of what I
wrote.

I'm guessing it gave up attempting to track the satellite with a PRN of 32.

Dave
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Re: [time-nuts] Why is holdover LED on HP 58503A not lit, when GPS lock is unlit too?

[Tim Shoppa]

A common misconception, is that holdover is the opposite of GPS lock.
Sometimes we might even talk about the two as if we're in one or the other.
But really the power-on state, is that we're in neither holdover or GPS
lock.

Holdover means the smartclock previously had GPS lock and had used it to
characterize the aging of the OCXO, and is maintaining the EFC
extrapolation, such that it believes it can still produce accurate time and
frequency through the GPS loss.

The state of your clock at the moment, is that it has never had GPS lock
since regaining power, it does not know what time it is, and it has not
characterized or extrapolated the aging of the OCXO. So it is definitely
not in holdover.

Tim N3QE

On Sun, Dec 18, 2016 at 8:01 AM, Dr. David Kirkby (Kirkby Microwave Ltd) <
drkir...@kirkbymicrowave.co.uk> wrote:

> My 58503 GPS time/frequency reference had its power disconnected a few
> times yesterday as I moved things in the lab. At the modem the status of
> the LEDs are
>
> * Power green
> * GPS lock - not lit
> * Holdover - not lit
> * Alarm - not lit.
>
> That is what the manual says will happen  when power is first applied, but
> I'm puzzled why.
>
> The SYSTEM:STATUS? shows the information at the end of this email. What I
> can't understand is why the holdover light is not lit, when clearly its not
> tracking any satellites. It seems logical to me that holdover should be on,
> when GPS lock is not, and visa versa. But that does not seem to be the
> case.
>
> Looking at the data below, the date/time is obviously wrong (01 Jan 1998),
> the height at -14.04 m  (MSL) is wrong, but latitude and longitude look
> about right, although they are certainly not exactly agreeing with Google
> maps, which show 51°39'04.1"N+0°46'36.4"E.
>
> I must be misunderstanding the purpose of these lights.
>
> I'm also a bit puzzled it has been on about 1.5 hours, and can't seem to
> find a single satellite. The antenna is fairly clear of anything else, and
> it was certainly working yesterday, with the power and GPS lock LEDs both
> lit.
>
> Any ideas what's going on?
>
> scpi > SYSTEM:STATUS?
> --- Receiver Status
> ---
>
> SYNCHRONIZATION ... [ Outputs
> Invalid ]
> SmartClock Mode ___   Reference Outputs
> ___
>Locked TFOM 9
> FFOM 3
>Recovery   1PPS TI  --
>Holdover   HOLD THR 1.000 us
> >> Power-up: GPS acquisition  Holdover Uncertainty
> 
>   Predict  --
>
> ACQUISITION .. [ GPS 1PPS
> Invalid ]
> Tracking: 0    Not Tracking: 1    Time _ +1 leap second
> pending
>PRN  El  AzUTC  12:59:16 [?] 01 Jan
> 1998
>*32  -- ---GPS 1PPS Invalid: not
> tracking
>   ANT DLY  0 ns
>   Position
> 
>   MODE Survey:  0%
> complete
>Suspended: track <4
> sats
>   INIT LAT N  51:39:03.825
>   INIT LON E   0:46:36.278
> ELEV MASK 10 deg   *attempting to track   INIT HGT  -14.04 m
> (MSL)
> HEALTH MONITOR . [
> OK ]
> Self Test: OKInt Pwr: OK   Oven Pwr: OK   OCXO: OK   EFC: OK   GPS Rcv:
> OK
> scpi >
>
>
>
> Dr. David Kirkby Ph.D CEng MIET
> Kirkby Microwave Ltd
> Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
> UK.
> Registered in England and Wales, company number 08914892.
> http://www.kirkbymicrowave.co.uk/
> Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)
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>
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Re: [time-nuts] Why is holdover LED on HP 58503A not lit, when GPS lock is unlit too?

[Artek Manuals]

I believe  the "Holdover" function only occurs when you you loose just 
the  satellites


Once locked disconnect the antenna for a minute and you will see the 
holdover LED light.


IF the unit looses POWER it has no way of of powering the oscillator and 
its ovens ( to do a holdover) and has no way of knowing how long the 
unit has been off when re-powered until it goes through a complete 
acquisition/re-sync cycle.


DAVE

manu...@artekmanuals.com


On 12/18/2016 8:01 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:

My 58503 GPS time/frequency reference had its power disconnected a few
times yesterday as I moved things in the lab. At the modem the status of
the LEDs are

* Power green
* GPS lock - not lit
* Holdover - not lit
* Alarm - not lit.

That is what the manual says will happen  when power is first applied, but
I'm puzzled why.

The SYSTEM:STATUS? shows the information at the end of this email. What I
can't understand is why the holdover light is not lit, when clearly its not
tracking any satellites. It seems logical to me that holdover should be on,
when GPS lock is not, and visa versa. But that does not seem to be the
case.

Looking at the data below, the date/time is obviously wrong (01 Jan 1998),
the height at -14.04 m  (MSL) is wrong, but latitude and longitude look
about right, although they are certainly not exactly agreeing with Google
maps, which show 51°39'04.1"N+0°46'36.4"E.

I must be misunderstanding the purpose of these lights.

I'm also a bit puzzled it has been on about 1.5 hours, and can't seem to
find a single satellite. The antenna is fairly clear of anything else, and
it was certainly working yesterday, with the power and GPS lock LEDs both
lit.

Any ideas what's going on?

scpi > SYSTEM:STATUS?
--- Receiver Status
---

SYNCHRONIZATION ... [ Outputs
Invalid ]
SmartClock Mode ___   Reference Outputs
___
Locked TFOM 9
FFOM 3
Recovery   1PPS TI  --
Holdover   HOLD THR 1.000 us

Power-up: GPS acquisition  Holdover Uncertainty


   Predict  --

ACQUISITION .. [ GPS 1PPS
Invalid ]
Tracking: 0    Not Tracking: 1    Time _ +1 leap second
pending
PRN  El  AzUTC  12:59:16 [?] 01 Jan
1998
*32  -- ---GPS 1PPS Invalid: not tracking
   ANT DLY  0 ns
   Position

   MODE Survey:  0%
complete
Suspended: track <4
sats
   INIT LAT N  51:39:03.825
   INIT LON E   0:46:36.278
ELEV MASK 10 deg   *attempting to track   INIT HGT  -14.04 m
(MSL)
HEALTH MONITOR . [
OK ]
Self Test: OKInt Pwr: OK   Oven Pwr: OK   OCXO: OK   EFC: OK   GPS Rcv:
OK
scpi >



Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
UK.
Registered in England and Wales, company number 08914892.
http://www.kirkbymicrowave.co.uk/
Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)
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--
Dave
manu...@artekmanuals.com
www.ArtekManuals.com

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Re: [time-nuts] FPGA based TDC

[Bob Camp]

Hi

> On Dec 18, 2016, at 7:46 AM, Attila Kinali  wrote:
> 
> On Sat, 17 Dec 2016 10:48:35 -0500
> Bob Camp  wrote:
> 
>>> Sébastian told me that for the original TDC design (based on a Spartan3 
>>> IIRC)
>>> they didn't employ any method for increasing the resolution by compensating
>>> for different bin sizes, as they got pretty close to the minimal bin size
>>> anyways. But for the Cyclone4 I guess using something like Wu's Wave 
>>> Union[4]
>>> approach might be a good idea. Unfortunately, we didn't have the time to 
>>> try it.
>> 
>> If you do go to the Wave Union, it does work on Cyclone 5’s and Spartan 6’s. 
>> I suspect 
>> it will work on the newer stuff as well. The big issue you run into is 
>> “decoding” the patterns
>> you get. The data is *not* a nice looking set of “all zeros before” and “all 
>> ones after” some
>> point. Figuring out which bin came first with a random calibration approach 
>> requires a 
>> bit of a leap of faith (count the zeros / count the ones) to order them. 
>> Even with that you 
>> still get bins that appear to be equivalent (same number of zeros), but have 
>> them in a 
>> different order. 
> 
> Yes, the decoding of wave union is anything but trivial. The main issue
> is that the ordering of the thermometer encoded bits is not the same as
> the ordering of the delay line. This is due to the badly controlled delays
> within the delay line and the clock tree causing unequal capture time for
> the registers. This leads to "bubbles" in the encoding. The original TDC Core
> code reordered the bits according to the timing simulation results.
> For the Cyclone4 we encountered the problem, that the ordering is not stable.
> i.e. the ordering changes over time and is dependent on the logic
> surrounding the delay line. Thus we reverted to only count the zeros/ones as
> an approximation. This of course does not work with wave union and an
> other scheme as to be devised. One way to do it would probably be to make
> the distance between the edges long enough such that the bubles can be
> matched to a single edge. Then one could count the zeros/ones in the area
> around the presumed edge position. But as I have not tried this, I do not
> know how well it would work in reality.


It does work, but it is a bit messy. The number of “indeterminate” states 
starts to get
a bit alarming. Without a fancy system to actually figure out what is what ( = 
a generator 
that steps off at 1 ps resolution with jitter < 0.1 ps) there is a lot of 
“faith”involved. 

You also can do the same things with multiple delay lines. The assumption is 
that the
odd stuff will not happen at the same places. At least with my limited skills, 
that turned
out to be a poor assumption. The problems occurred to often and they pretty much
*always* lined up. 

The scary part is that you can come up with issues like crosstalk that can turn 
the 
system into something a bit non-random. There have to be sensitivities like that
on the die. It’s just a question of if they are large enough to matter in this 
case …

Back to shopping the auction sites for that generator. I’ve got $20 as my max 
bid :)

Bob

> 
>   Attila Kinali
> 
> -- 
> Malek's Law:
>Any simple idea will be worded in the most complicated way.
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Re: [time-nuts] Lady Heather for homebrew GPSDO

[Bob Camp]

Hi

If your GPSDO is based on an quad core 1.8 GHz with 4 GB of RAM, you can 
implement 
a lot of things. Effectively your GPSDO has more horsepower than a lot of the 
computers 
people are using to monitor GPSDO’s. Given the economics of silicon, that’s 
still not a 
crazy expensive CPU to use.

If you are trying to cram your GPSDO into a PIC 16, coming up with complex 
structures for
the i/o is likely to be a bit of a challenge. Most of the poor little beast is 
already tied up trying
to keep up with the main work of the device. 

Writing and *debugging* a binary protocol is a lot more involved than a serial 
stream. You
can argue that code it code and it’s all trivial. It’s also been argued that 
coming up with a 
fully working GPSDO is a 10 minute project. 

I don’t have a GPSDO project hidden somewhere under all this junk on the bench. 
I’m not
planning to do one any time soon. I’m just a casual observer in all this. To me 
dumping stuff
into an already existing NMEA message parser seems to be the more universal way 
to go.
It’s not without it’s issues. Based on doing this from scratch on a few hundred 
times on 
various devices, it’s generally been the quicker and easier way to go. It’s 
certainly not the 
only way….

Bob


> On Dec 18, 2016, at 12:02 AM, Mark Sims  wrote:
> 
>> NMEA is a fine interface, widely used, easy to play with. There's no need to 
>> be pejorative.
> 
> Not being perjorative...  just commenting that it would be a lot easier to 
> implement than TSIP... probably not as good, but a lot easier to code... the 
> lazy bastards way...  I'm a lazy bastard, too.
> 
> 
>> I don't know what your problem is with the Z3801A
> 
> SCPI is good interface.  The main problem with the Z3801A implementation is 
> that it does not tag its responses with some kind of identifier as to what 
> the response is.  This is a HUGE mistake that only a novice protocol designer 
> would make.  It barely makes sense if only a person at a keyboard would be 
> sending commands.   If anything hiccups the communications a computer can 
> wind up interpreting the data improperly is that response a DAC voltage?  
> a temperature?  yeah, I asked for a DAC voltage but you sent me the 
> temperature I asked for last time...  they look identical...   there's no way 
> to tell FOR SURE what I actually got...   No amount of state machine foo can 
> get around it.
> 
> 
>> So this is all the more reason to re-consider your LH architecture and not 
>> assume or not depend on the input(s) being externally timed or paced at 
>> exact multiples of 1 s.
> 
> Heather does not depend upon a 1 Hz update message.  I've tested it with 1Hz 
> to 50 Hz receivers (things do get a bit wonky at over 20 Hz... too much data 
> coming over too small of a USB/serial pipe).  Heather uses the message that 
> contains the time code to decide when to update the display... it's a GPS 
> monitoring program after all and GPS is all about time.It could just as 
> easily be set up to use any message or event or timer or mule kick.  The 
> receiver time code message is the most universally consistent thing across 
> all the devices Heather works with, so that's what gets used.
> 
> 
> 
> 
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Re: [time-nuts] FPGA based TDC

[Attila Kinali]

On Sat, 17 Dec 2016 10:48:35 -0500
Bob Camp  wrote:

> > Sébastian told me that for the original TDC design (based on a Spartan3 
> > IIRC)
> > they didn't employ any method for increasing the resolution by compensating
> > for different bin sizes, as they got pretty close to the minimal bin size
> > anyways. But for the Cyclone4 I guess using something like Wu's Wave 
> > Union[4]
> > approach might be a good idea. Unfortunately, we didn't have the time to 
> > try it.
> 
> If you do go to the Wave Union, it does work on Cyclone 5’s and Spartan 6’s. 
> I suspect 
> it will work on the newer stuff as well. The big issue you run into is 
> “decoding” the patterns
> you get. The data is *not* a nice looking set of “all zeros before” and “all 
> ones after” some
> point. Figuring out which bin came first with a random calibration approach 
> requires a 
> bit of a leap of faith (count the zeros / count the ones) to order them. Even 
> with that you 
> still get bins that appear to be equivalent (same number of zeros), but have 
> them in a 
> different order. 

Yes, the decoding of wave union is anything but trivial. The main issue
is that the ordering of the thermometer encoded bits is not the same as
the ordering of the delay line. This is due to the badly controlled delays
within the delay line and the clock tree causing unequal capture time for
the registers. This leads to "bubbles" in the encoding. The original TDC Core
code reordered the bits according to the timing simulation results.
For the Cyclone4 we encountered the problem, that the ordering is not stable.
i.e. the ordering changes over time and is dependent on the logic
surrounding the delay line. Thus we reverted to only count the zeros/ones as
an approximation. This of course does not work with wave union and an
other scheme as to be devised. One way to do it would probably be to make
the distance between the edges long enough such that the bubles can be
matched to a single edge. Then one could count the zeros/ones in the area
around the presumed edge position. But as I have not tried this, I do not
know how well it would work in reality.

Attila Kinali

-- 
Malek's Law:
Any simple idea will be worded in the most complicated way.
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[time-nuts] Why is holdover LED on HP 58503A not lit, when GPS lock is unlit too?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

My 58503 GPS time/frequency reference had its power disconnected a few
times yesterday as I moved things in the lab. At the modem the status of
the LEDs are

* Power green
* GPS lock - not lit
* Holdover - not lit
* Alarm - not lit.

That is what the manual says will happen  when power is first applied, but
I'm puzzled why.

The SYSTEM:STATUS? shows the information at the end of this email. What I
can't understand is why the holdover light is not lit, when clearly its not
tracking any satellites. It seems logical to me that holdover should be on,
when GPS lock is not, and visa versa. But that does not seem to be the
case.

Looking at the data below, the date/time is obviously wrong (01 Jan 1998),
the height at -14.04 m  (MSL) is wrong, but latitude and longitude look
about right, although they are certainly not exactly agreeing with Google
maps, which show 51°39'04.1"N+0°46'36.4"E.

I must be misunderstanding the purpose of these lights.

I'm also a bit puzzled it has been on about 1.5 hours, and can't seem to
find a single satellite. The antenna is fairly clear of anything else, and
it was certainly working yesterday, with the power and GPS lock LEDs both
lit.

Any ideas what's going on?

scpi > SYSTEM:STATUS?
--- Receiver Status
---

SYNCHRONIZATION ... [ Outputs
Invalid ]
SmartClock Mode ___   Reference Outputs
___
   Locked TFOM 9
FFOM 3
   Recovery   1PPS TI  --
   Holdover   HOLD THR 1.000 us
>> Power-up: GPS acquisition  Holdover Uncertainty

  Predict  --

ACQUISITION .. [ GPS 1PPS
Invalid ]
Tracking: 0    Not Tracking: 1    Time _ +1 leap second
pending
   PRN  El  AzUTC  12:59:16 [?] 01 Jan
1998
   *32  -- ---GPS 1PPS Invalid: not tracking
  ANT DLY  0 ns
  Position

  MODE Survey:  0%
complete
   Suspended: track <4
sats
  INIT LAT N  51:39:03.825
  INIT LON E   0:46:36.278
ELEV MASK 10 deg   *attempting to track   INIT HGT  -14.04 m
(MSL)
HEALTH MONITOR . [
OK ]
Self Test: OKInt Pwr: OK   Oven Pwr: OK   OCXO: OK   EFC: OK   GPS Rcv:
OK
scpi >



Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
UK.
Registered in England and Wales, company number 08914892.
http://www.kirkbymicrowave.co.uk/
Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)
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[time-nuts] Lady Heather for homebrew GPSDO

[Mark Sims]

>  NMEA is a fine interface, widely used, easy to play with. There's no need to 
> be pejorative.

Not being perjorative...  just commenting that it would be a lot easier to 
implement than TSIP... probably not as good, but a lot easier to code... the 
lazy bastards way...  I'm a lazy bastard, too.


> I don't know what your problem is with the Z3801A

SCPI is good interface.  The main problem with the Z3801A implementation is 
that it does not tag its responses with some kind of identifier as to what the 
response is.  This is a HUGE mistake that only a novice protocol designer would 
make.  It barely makes sense if only a person at a keyboard would be sending 
commands.   If anything hiccups the communications a computer can wind up 
interpreting the data improperly is that response a DAC voltage?  a 
temperature?  yeah, I asked for a DAC voltage but you sent me the temperature I 
asked for last time...  they look identical...   there's no way to tell FOR 
SURE what I actually got...   No amount of state machine foo can get around it.


> So this is all the more reason to re-consider your LH architecture and not 
> assume or not depend on the input(s) being externally timed or paced at exact 
> multiples of 1 s.

Heather does not depend upon a 1 Hz update message.  I've tested it with 1Hz to 
50 Hz receivers (things do get a bit wonky at over 20 Hz... too much data 
coming over too small of a USB/serial pipe).  Heather uses the message that 
contains the time code to decide when to update the display... it's a GPS 
monitoring program after all and GPS is all about time.It could just as 
easily be set up to use any message or event or timer or mule kick.  The 
receiver time code message is the most universally consistent thing across all 
the devices Heather works with, so that's what gets used.




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