date:20160614

Hi

With some searching and dedicated bidding, you can find older L1/L2 GPS 
gear fairly cheaply. It may take a year or two of bidding to get something you
can use….That gets you back to the issue of “am I fiddling around waiting 
to do something or doing it”. 

Bob

> On Jun 14, 2016, at 4:16 AM, Angus  wrote:
> 
> Hi,
> 
> I'm planning to test some rubidiums again, but since Santa never did
> get me that hydrogen maser I asked for, I'm still stuck with ordinary
> gps timing receivers as a separate medium to long term reference. The
> atmospheric issues are probably the main ones I would like to get rid
> of, although the more errors removed the better.
> 
> It does not have to be done in real time, but even an single test run
> would last weeks, so there could be a lot of data to tie together.
> 
> It would really need to be something that actually exists rather than
> just an idea of how it might be done, since I really just don't have
> time for any more major projects anytime soon. I've found from
> experience that too much time spent making the test gear etc means
> that I don't get the time to actually use it!
> 
> I'm also looking for something that's not too expensive - like up to
> hundreds rather than thousands of pounds.
> A good cesium or 2+ frequency gps with relevant options might be fine,
> but also rather out of my price range. 
> 
> BTW, I do plan on uploading the end results, in case anyone is
> interested.
> 
> 
> If anyone knows of some way to do this, (or even has something
> appropriate they want to sell) I'd appreciate hearing about it, on or
> off-list.
> 
> Thanks,
> Angus.
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Re: [time-nuts] DIY TimePod

Hi

Since (in a sense) it’s a single frequency SDR, it very much looks at the 
fundamental sine wave
component. 

Bob

> On Jun 14, 2016, at 8:53 PM, John Swenson  wrote:
> 
> Got it, I missed the 27 MHz low pass filter with 60 db attenuation. So the 
> ADC really is mostly seeing a sine wave.
> 
> I guess it's back to the drawing board and doing this with the filter and the 
> ADCs.
> 
> Thanks for setting me straight on this.
> 
> John S.
> 
> 
> On 6/14/2016 3:01 PM, Chris Caudle wrote:
>> On Tue, June 14, 2016 2:35 am, John Swenson wrote:
>>> The idea here is around a 80MHz sample clock with a
>>> maximum input/ref signal of around 25MHz.
>> 
>> Without some pretty steep low pass filtering that will violate the Nyquist
>> criterion (for 80MHz sample clock the input must be strictly limited to
>> less than 40MHz).  You can't even get the first odd harmonic in of a 25MHz
>> square wave input.
>> 
>>> This is based on the TimePod with ADCs, which is
>>> supposed to work with square waves.
>> 
>> The ADC's would have a low pass filter in front.  Think of it in terms of
>> the Shannon information capacity, the amount of information conveyed is
>> determined by the bandwidth and the signal to noise ratio.  The bandwidth
>> is determined by the sample rate, the signal to noise ratio by the number
>> of (effective) bits of the ADC.
>> I forget which ADC someone mentioned recently as being in the TimePod.
>> Isn't it a 16 bit converter?  So that is getting around 96dB integrated
>> signal to noise ratio per converter, and you are starting with 6dB.
>> 
>>> When you feed a square wave into this you have several samples at say
>>> 50, then it jumps to 50,000 stays there for several samples, then jumps
>>> down to 50 again.
>> 
>> The key thing you are missing which happens with a multi-bit ADC is that
>> the signal has a finite rise time, so it doesn't "jump" to 50,000, it has
>> a transition region where you get several samples of different values.
>> Those samples fit an infinite number of possible signals, but only one
>> signal which is limited to the Nyquist criterion bandwidth.  Using those
>> samples and the knowledge of the system bandwidth you can interpolate
>> where the zero crossing must have been.
>> 
>> With a single bit quantizer (and no feedback to shape the noise), you get
>> very little information about the signal values in the transition region.
>> 
>>> This still seems like a binary sample. The difference
>>> is that every now and then the sample hits during a ramptime of the
>>> square wave and will give some intermediate value,
>> 
>> No, every time you will sample during the transition, because the "square"
>> wave still has a finite rise time, and if you have properly bandwidth
>> limited the signal as required by the Nyquist sampling criterion (input
>> signal must be less than half the frequency of the sampling clock) then
>> you know what the upper limit on the rise time is.
>> 
> 
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Re: [time-nuts] DIY TimePod

2016-06-14 Thread John Swenson

Got it, I missed the 27 MHz low pass filter with 60 db attenuation. So 
the ADC really is mostly seeing a sine wave.


I guess it's back to the drawing board and doing this with the filter 
and the ADCs.


Thanks for setting me straight on this.

John S.


On 6/14/2016 3:01 PM, Chris Caudle wrote:

On Tue, June 14, 2016 2:35 am, John Swenson wrote:

The idea here is around a 80MHz sample clock with a
maximum input/ref signal of around 25MHz.


Without some pretty steep low pass filtering that will violate the Nyquist
criterion (for 80MHz sample clock the input must be strictly limited to
less than 40MHz).  You can't even get the first odd harmonic in of a 25MHz
square wave input.


This is based on the TimePod with ADCs, which is
supposed to work with square waves.


The ADC's would have a low pass filter in front.  Think of it in terms of
the Shannon information capacity, the amount of information conveyed is
determined by the bandwidth and the signal to noise ratio.  The bandwidth
is determined by the sample rate, the signal to noise ratio by the number
of (effective) bits of the ADC.
I forget which ADC someone mentioned recently as being in the TimePod.
Isn't it a 16 bit converter?  So that is getting around 96dB integrated
signal to noise ratio per converter, and you are starting with 6dB.


When you feed a square wave into this you have several samples at say
50, then it jumps to 50,000 stays there for several samples, then jumps
down to 50 again.


The key thing you are missing which happens with a multi-bit ADC is that
the signal has a finite rise time, so it doesn't "jump" to 50,000, it has
a transition region where you get several samples of different values.
Those samples fit an infinite number of possible signals, but only one
signal which is limited to the Nyquist criterion bandwidth.  Using those
samples and the knowledge of the system bandwidth you can interpolate
where the zero crossing must have been.

With a single bit quantizer (and no feedback to shape the noise), you get
very little information about the signal values in the transition region.


This still seems like a binary sample. The difference
is that every now and then the sample hits during a ramptime of the
square wave and will give some intermediate value,


No, every time you will sample during the transition, because the "square"
wave still has a finite rise time, and if you have properly bandwidth
limited the signal as required by the Nyquist sampling criterion (input
signal must be less than half the frequency of the sampling clock) then
you know what the upper limit on the rise time is.



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[time-nuts] u-blox "naked" chips - anyone brave enough to try them?

Moin,

Some of you might know that the u-blox chips are available in small
quantities and for quite cheap too. Just go to aliexpress or taobao
and type in "UBX-G7020" or "UBX-M8030" and you will get plenty of
results. My guess is, that these chips are leftovers from cellphone
production that get sold off close at wholesale price (I've seen
that with other chips as well). So it is likely that these are
actually genuine chips.

Now, the documentation for those chips is not that readily available.
But fret not! Some of it can be found if you look hard enough. At least
for the G7020. I think, this information should be enough for anyone
who wants to build his own GPSDO with Trimble like oscillator control
(ie that the reference oscillator of the GPS module is steered directly).

The UBX-M8030-KT, which would be a timing chip and thus for sure
support the RAW data commandos, is unfortunately quite google proof.
At least I couldn't find any documentation for those but the official
public one provided by u-blox. I would guess, that the pin out is very
similar if not the same, but without guarante.

(I know that least the UBX-M8030-KT datasheet UBX-13001634 is floating
around, but So far i was not able to get hold of it, due to insufficient
chinese language skills)

As for the UBX-G7020, you can find the following documents:

UBX-G7020-KT/KA u-blox 7 GPS/GNSS chips Data Sheet GPS.G7-HW-12001
https://raw.githubusercontent.com/ArdentHeavyIndustries/straightedge-gps-firmware/master/Datasheets/UBX-G7020-Kx_DataSheet_(GPS%20G7-HW-12001)_Confidential.pdf.pdf

u-blox 7 GPS/GNSS chips Hardware Integration Manual GPS.G7-HW-10003
https://www.olimex.com/Products/Modules/GPS/MOD-GPS/resources/UBX-G7020_HardwareIntegrationManual_-GPS.G7-HW-10003-_Confidential.pdf

So, if anyone would want to give those a try, let us know.
I'm sure many here would be interested.

Attila Kinali

--
Malek's Law:
Any simple idea will be worded in the most complicated way.
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[time-nuts] Rare Symmetricom X72 with 1pps input available

2016-06-14 Thread Skip Withrow

Hello time-nuts,

I have available a Symmetricom X72 rubidium oscillator with version 5.08
firmware.  This firmware has the code to discipline the X72 to an external
1pps input.  Unit has been checked out (including 1pps disciplining) and
appears to be in good working condition.  Oscillator comes with one of the
adapter boards just like the non-pps units that we sell on ebay (check out
auction 361567934794), pin-6 is jumpered to provide the 1pps to the X72
(pin 19).  There is also a link to the manual in the ebay auction which has
a lot more on the 1pps disciplining function.

Yes, there are both pros and cons to the X72.  Being very small its
performance won't match an HP5065A.  However, being very small makes it
very portable, it has the GPSDO built in (damping can be set from 0.25 -
4.0, time constant can be set from 0 - 100,000 seconds), and power can be
10-32 volts DC.

Unit is being offered for $225 and includes shipping to the U.S.  First
email to s...@rdrelectronics.com wins, I will send you payment information.

If you miss this one and would like to be put on a waiting list please let
me know, I hope to have more in the future.

Regards,
Skip Withrow
RDR Electronics, Inc.
303-790-1830




Virus-free.
www.avast.com

<#DDB4FAA8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
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Re: [time-nuts] DIY TimePod

2016-06-14 Thread Chris Caudle

On Tue, June 14, 2016 2:35 am, John Swenson wrote:
> The idea here is around a 80MHz sample clock with a
> maximum input/ref signal of around 25MHz.

Without some pretty steep low pass filtering that will violate the Nyquist
criterion (for 80MHz sample clock the input must be strictly limited to
less than 40MHz).  You can't even get the first odd harmonic in of a 25MHz
square wave input.

> This is based on the TimePod with ADCs, which is
> supposed to work with square waves.

The ADC's would have a low pass filter in front.  Think of it in terms of
the Shannon information capacity, the amount of information conveyed is
determined by the bandwidth and the signal to noise ratio.  The bandwidth
is determined by the sample rate, the signal to noise ratio by the number
of (effective) bits of the ADC.
I forget which ADC someone mentioned recently as being in the TimePod. 
Isn't it a 16 bit converter?  So that is getting around 96dB integrated
signal to noise ratio per converter, and you are starting with 6dB.

> When you feed a square wave into this you have several samples at say
> 50, then it jumps to 50,000 stays there for several samples, then jumps
> down to 50 again.

The key thing you are missing which happens with a multi-bit ADC is that
the signal has a finite rise time, so it doesn't "jump" to 50,000, it has
a transition region where you get several samples of different values. 
Those samples fit an infinite number of possible signals, but only one
signal which is limited to the Nyquist criterion bandwidth.  Using those
samples and the knowledge of the system bandwidth you can interpolate
where the zero crossing must have been.

With a single bit quantizer (and no feedback to shape the noise), you get
very little information about the signal values in the transition region.

> This still seems like a binary sample. The difference
> is that every now and then the sample hits during a ramptime of the
> square wave and will give some intermediate value,

No, every time you will sample during the transition, because the "square"
wave still has a finite rise time, and if you have properly bandwidth
limited the signal as required by the Nyquist sampling criterion (input
signal must be less than half the frequency of the sampling clock) then
you know what the upper limit on the rise time is.

-- 
Chris Caudle

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Re: [time-nuts] Improving on basic L1 timing

2016-06-14 Thread Michael Wouters

If you followed the link to www.openttp.org and are wondering where the
software is, follow the link on the home page to GitHub and then look in
the Develop branch. The ublox branch is for the new '8' series receivers.

Cheers
Michael

On Tuesday, 14 June 2016, Michael Wouters  wrote:

> Hello Angus
>
> If you have 3 rubidiums of similar stability + 3 counters, you could
> do a 3-cornered hat.
>
> Otherwise, GPS common view to a better clock may be an option. If you
> are reasonably close to a national standards lab, you might be able to
> use their time-transfer files to compare your rubidiums with their
> time scale - not everyone makes them publically available though.
> Otherwise, if there is an IGS station near you, you could use the
> station RINEX files and IGS clock solutions which are freely
> available. Many IGS stations have a H-maser as the local clock. But it
> may be just as good to simply use the comparison with GPS time
> inherent in the time-transfer file.
>
> The advantage of generating a time-transfer file is the possibility of
> then improving upon the various corrections broadcast by GPS,
> effectively repeating what the GPS receiver does to generate its
> realization of GPS time but with better data.
>
> With post-processing, the short to medium term (less than 1 day)
> performance  can be improved a bit as you are suggesting when you
> referred to "atmospheric issues". Improved ionospheric models are
> available  or if there is an IGS station nearby, for example, the
> measured ionosphere could be used. Other improvements can be had with
> good antenna coordinates and using final orbits in the processing.
>
> What can you use for your time-transfer receiver ? Some low-cost
> single-frequency receivers are suitable eg the Trimble Resolution T.
> The essential requirement is the availability of  raw code
> measurements - with these you can generate CGGTTS time-transfer files
> and/or RINEX observation files.
>
> At least part of the software infrastructure to do this exists: the
> OpenTTP project (www.openttp.org) has software for CGGTTS and RINEX
> file generation for a few older,single frequency receivers, with
> support for some other,current receivers under active development.
> There is other software around, but it is orientated towards dual
> frequency receivers and carrier phase processing.
>
> Although it would be relatively straightforward to hack in use of
> improved ionosphere, using final orbits is a bit harder since these
> are not parameterized the same way as the broadcast orbits. Maybe
> someone on time-nuts has software to do the conversion (and this would
> have to be hacked into the OpenTTP software, rather than the final
> time comparison).
>
> The sort of performance you get on a zero baseline is a TDEV of a few
> ns - you can extrapolate frequency stability from that.
> On a 1000 km baseline, you can compare two Cs to better than 1 part in
> 10^13 @ 1 day.
>
> All of the above is software-oriented, whereas you seem to be looking
> for a hardware solution, but that's what I know best.
>
> Cheers
> Michael
>
> On Tue, Jun 14, 2016 at 6:16 PM, Angus  > wrote:
> > Hi,
> >
> > I'm planning to test some rubidiums again, but since Santa never did
> > get me that hydrogen maser I asked for, I'm still stuck with ordinary
> > gps timing receivers as a separate medium to long term reference. The
> > atmospheric issues are probably the main ones I would like to get rid
> > of, although the more errors removed the better.
> >
> > It does not have to be done in real time, but even an single test run
> > would last weeks, so there could be a lot of data to tie together.
> >
> > It would really need to be something that actually exists rather than
> > just an idea of how it might be done, since I really just don't have
> > time for any more major projects anytime soon. I've found from
> > experience that too much time spent making the test gear etc means
> > that I don't get the time to actually use it!
> >
> > I'm also looking for something that's not too expensive - like up to
> > hundreds rather than thousands of pounds.
> > A good cesium or 2+ frequency gps with relevant options might be fine,
> > but also rather out of my price range.
> >
> > BTW, I do plan on uploading the end results, in case anyone is
> > interested.
> >
> >
> > If anyone knows of some way to do this, (or even has something
> > appropriate they want to sell) I'd appreciate hearing about it, on or
> > off-list.
> >
> > Thanks,
> > Angus.
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Re: [time-nuts] RS232 / GPS interface/prototyping board

2016-06-14 Thread Gary E. Miller

Yo Attila!

First, my apologes for getting this thread started.  I misunderstood
Mark's design to have USB, when in fact it did not.  Late night brain
fart.  So any USB discussion is unrelated to his work.

On Tue, 14 Jun 2016 21:49:17 +0200
Attila Kinali  wrote:

> Of the devices you mentioned above, all are USB2.0, but only
> the FT2232H and the FT4232H are HS, the FT232R is FS only.
> Ie, while the FT2232H and the FT4232H support transfer speeds
> up to 12MByte/s, the FT232R supports only 3Mbyte/s
> (Rule of thumb: if the FTDI serial chip's name doesn't contain
> a H, it's most likely not a HS device)

I 100% agree with Attila.  The problem is all USB 1.1 devices are by
definition USB 2.0 Compliant.  So in a sense Herbet is right.  He is
corectly reading the marketing literature that says "USB 2.0".  

But, I refuse to say a device is USB 2.0 unless it actually does
something that is in the USB 2.0 spec and not the USB 1.1 spec.  That
usually mean High Speed instead of Full Speed.

I know that PPS over USB is laughable to a time-nut, but to me the
approximately 8x improvement in precision is very noticeable for
any host (laptop/desktop) unlucky enough to not have a real serial port

Full Speed is polled about every 1 milliSec, High speed is polled about
every 125 microSec.  A real serial port can get down to a microSec, or
better, and of course even that is laughable to most of you guys, but I'm
looking more mass market.

Once again, sorry to start the confusion...

RGDS
GARY
---
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@rellim.com  Tel:+1 541 382 8588

pgpf_Y70qxVfs.pgp
Description: OpenPGP digital signature
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Re: [time-nuts] Ebay LEA-6T hockey pucks

On Tue, 14 Jun 2016 17:05:21 +
Mark Sims  wrote:

> I got in one of those LEA-6T hockey puck gizmos from China off of Ebay
> ($30,  OK, I paid $40 to get it quicker (3 days) from a US seller).
> It seems to work fine.  I connected it to one of my RS-232 level converter
> boards by hacking off one of the hockey puck cable connectors and wiring it
> directly to my level converter board.  The pucks can speak over USB or
> serial (default is 9600:8N1).   It has a regulator for dropping USB 5V down
> to 3.3V,  but works fine with 3.3V in.  There is a nice teardown and
> discussion about these on EEVBLOG:

If someone has one of these LEA-6T modules to spare. I would like to see
the inards of one. The one-shield-over-analog-and-digital part seems weird.
I wonder what's really inside.

Attila Kinali

-- 
Malek's Law:
Any simple idea will be worded in the most complicated way.
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Re: [time-nuts] RS232 / GPS interface/prototyping board

On Tue, 14 Jun 2016 18:39:35 +0200
Herbert Poetzl  wrote:

> > I am not aware of any USB 2 UART devices (that doesn’t
> > necessarily mean much). They just don’t need to be that fast.
> 
> All modern FTDIs are USB 2.0 (for example the FT232R,
> FT2232H and FT4232H) because they also allow for other
> types of data transfer besides the UART which require
> USB 2.0.

This is not completely correct. The main difference between
USB1.1 and USB2.0 are (small) changes in the descriptor tables
and the introduction of HighSpeed transfer speed (aka HS aka 480Mbit/s,
or what most people call USB2.0). No additonal data transfer type was
added, as the three available (Bulk, Interrupt and Isochronus)
were sufficient. None of these changes have anything to
do with what kind of device types (UART is just a device type)
are possible. There are plenty of UARTS that are USB1.1.

Most devices these days will be USB2.0 conform. Meaning that
their descriptor tables will follow the changed layout from
the new standard. It does not mean that they are HS devices.
Actually most I have encountered are still FullSpeed (aka FS aka 12Mbit/s)
devices. There are some HS UART's though, FTDI selling some of them.

The maximum transfer speed a HS device can achieve with
bulk transfers is 35MByte/s (due to overhead in the protocol
and reserved time slots). But only if the devices is done in
an intelligent way and is able to transfer the data in blocks
of 512byte. If smaller blocks are used, then the data rate
scales down accordingly.

Of the devices you mentioned above, all are USB2.0, but only
the FT2232H and the FT4232H are HS, the FT232R is FS only.
Ie, while the FT2232H and the FT4232H support transfer speeds
up to 12MByte/s, the FT232R supports only 3Mbyte/s
(Rule of thumb: if the FTDI serial chip's name doesn't contain
a H, it's most likely not a HS device)

Attila Kinali

-- 
Malek's Law:
Any simple idea will be worded in the most complicated way.
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[time-nuts] TU60-D120-131 Specs....?

They run on 5V,  talk either Motorola binary (default at power-on) or Zodiac 
binary (serial data at 9600:8N1).  The antenna connector is MCX.  The one I got 
in last week does not have any GPS week rollover problems.  
Their Motorola binary mode seems to have issues setting TRAIM parameters using 
Motorola commands...  works fine using the Zodiac commands.   Hint: beware of 
any receivers that emulate Motorola binary (or any other receiver language)... 
all of them I have tested have some issues doing it.  It's best to run them in 
their native mode .
  
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[time-nuts] Ebay LEA-6T hockey pucks

The firmware in those LEA-6T Chinese hockey pucks outputs the RAW (carrier 
phase information) message!
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[time-nuts] Ebay LEA-6T hockey pucks

I got in one of those LEA-6T hockey puck gizmos from China off of Ebay ($30,  
OK, I paid $40 to get it quicker (3 days) from a US seller).   It seems to work 
fine.  I connected it to one of my RS-232 level converter boards by hacking off 
one of the hockey puck cable connectors and wiring it directly to my level 
converter board.  The pucks can speak over USB or serial (default is 9600:8N1). 
  It has a regulator for dropping USB 5V down to 3.3V,  but works fine with 
3.3V in.  There is a nice teardown and discussion about these on EEVBLOG:

http://www.eevblog.com/forum/projects/ebay-u-blox-lea-6t-gps-module-teardown-and-initial-test/

These are probably the cheapest and easiest way to get an LEA-6T,  but you 
would probably want to cobble on an external antenna connector. The timepulse 
signals are not brought out to the cables, but is easy to add.  There is a 
LED/transistor on PPS1 but you would probably want to change or remove that.  
PPS1 is connected directly to the base of the transistor so PPS1 gets clipped 
to a low level.

  
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Re: [time-nuts] TU60-D120-131 Specs....?

2016-06-14 Thread Dave M

Datasheet: 
http://www.rabel.org/archives/Navman_Jupiter_11_12/LA010050B_JupiterT_DataSheet.pdf
Example projects: 
http://www.jrmiller.demon.co.uk/projects/ministd/frqstd0.htm

http://www.vhfcomm.co.uk/GPS%20control.pdf

More info by searching Google for NAVMAN TU60-D120

Cheers,
Dave M


Bud Patten wrote:

Does anyone know anything about the TU60-D120-131 being offered on
ebay (voltage? 10Khz? 1 pps?, etc.) .   The seller tells me that he
doesn't know anything about the item he is selling..   ;-)   Any
input would be appreciated.



Regards,

Bud

ARS W0LCP 



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[time-nuts] TU60-D120-131 Specs....?

2016-06-14 Thread Bud Patten

Does anyone know anything about the TU60-D120-131 being offered on ebay
(voltage? 10Khz? 1 pps?, etc.) .   The seller tells me that he doesn't know
anything about the item he is selling..   ;-)   Any input would be
appreciated.

 

Regards,

Bud

ARS W0LCP

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Re: [time-nuts] Improving on basic L1 timing

On Tue, 14 Jun 2016 21:37:20 +1000
Michael Wouters  wrote:

> On Tue, Jun 14, 2016 at 6:16 PM, Angus  wrote:
> > I'm planning to test some rubidiums again, but since Santa never did
> > get me that hydrogen maser I asked for, I'm still stuck with ordinary
> > gps timing receivers as a separate medium to long term reference. The
> > atmospheric issues are probably the main ones I would like to get rid
> > of, although the more errors removed the better.

Make sure you have good skyview (aka good geometry) and very little
multipath. Both effects can affect the precision of your solution
much more than the ionospheric delay variation.

> Otherwise, GPS common view to a better clock may be an option. If you
> are reasonably close to a national standards lab, you might be able to
> use their time-transfer files to compare your rubidiums with their
> time scale - not everyone makes them publically available though.
> Otherwise, if there is an IGS station near you, you could use the
> station RINEX files and IGS clock solutions which are freely
> available. Many IGS stations have a H-maser as the local clock. But it
> may be just as good to simply use the comparison with GPS time
> inherent in the time-transfer file.

If you live in continental Europe, then you will inevitabely have an
IGS station nearby. They are everywhere! :-)

I wonder how good the final IGS solution for ionospheric and orbits
are, repectively how much you get out of waiting longer?
Especially if the next IGS station is more than a couple km away.
Does anyone have data on that?

> All of the above is software-oriented, whereas you seem to be looking
> for a hardware solution, but that's what I know best.
> and follow the instructions there.

I don't think you can get much better with an hardware only solution
than by using the IGS files. Even if an L1/L2 receiver gives you better
ionospheric estimates, the orbit uncertainties still need postprocessing
to be corrected.

The only other thing I can think of is using multiple Rb's as reference,
measure their temperature, air pressure and drift against GPS. Use all
this data to build a clock model (aka Kalman filter) that compensates
for temp/pressure/aging and measure the Rb under test against this ensemble.

But that's not something that already exists and is ready to use.
And I doubt that this can shave off much more than one order of magnitude
in ADEV.

Attila Kinali

-- 
Malek's Law:
Any simple idea will be worded in the most complicated way.
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Re: [time-nuts] RS232 / GPS interface/prototyping board

2016-06-14 Thread Herbert Poetzl

On Tue, Jun 14, 2016 at 07:19:54AM -0700, Nick Sayer via time-nuts wrote:
> That’s not a USB chip, it’s an RS-232 level converter.

> I am not aware of any USB 2 UART devices (that doesn’t
> necessarily mean much). They just don’t need to be that fast.

All modern FTDIs are USB 2.0 (for example the FT232R,
FT2232H and FT4232H) because they also allow for other
types of data transfer besides the UART which require
USB 2.0.

Best,
Herbert

>> On Jun 13, 2016, at 11:53 PM, Gary E. Miller  wrote:

>> Yo Mark!

>> On Tue, 14 Jun 2016 00:53:10 +
>> Mark Sims  wrote:

>>> The 1PPS signal is
>>> routed to the RS-232 connector via the MAX232A, 

>> Why did you use a USB 1.1 chip instead of a USB 2.0 chip?  The PPS
>> performance is much better with the Hi Speed chips.

>> RGDS
>> GARY
>> ---
>> Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
>>  g...@rellim.com  Tel:+1 541 382 8588
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Re: [time-nuts] RS232 / GPS interface/prototyping board

2016-06-14 Thread Nick Sayer via time-nuts

That’s not a USB chip, it’s an RS-232 level converter.

I am not aware of any USB 2 UART devices (that doesn’t necessarily mean much). 
They just don’t need to be that fast.

> On Jun 13, 2016, at 11:53 PM, Gary E. Miller  wrote:
> 
> Yo Mark!
> 
> On Tue, 14 Jun 2016 00:53:10 +
> Mark Sims  wrote:
> 
>> The 1PPS signal is
>> routed to the RS-232 connector via the MAX232A, 
> 
> Why did you use a USB 1.1 chip instead of a USB 2.0 chip?  The PPS
> performance is much better with the Hi Speed chips.
> 
> RGDS
> GARY
> ---
> Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
>   g...@rellim.com  Tel:+1 541 382 8588
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[time-nuts] RS232 / GPS interface/prototyping board

No USB on that board.  It is genuine hardware RS-232 via a DB9 connector.   No 
USB latency if your hardware supports it.  It does route the the PPS to the 
connector at RS-232 levels so you do have a propagation delay through the level 
shifters.  I tend to use real RS-232 interfaces instead of USB because 
micro-controllers have much better (and easier) support for it... plus I live 
in the Land of the Obsolete...  Also the board can be used as a general RS-232 
level shifter for other projects...  

I added the ATTINY pads for making a device  with a 10 degree of freedom IMU 
board...   I use the low order bits from the noisy readings of the MEMS IMU 
sensors to generate cryptographically secure true random numbers.The 
numbers that it generates pass all statistics tests for randomness.  Plus  the 
IMU can detect movement of and tampering with the device and generate an alarm.


  
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Re: [time-nuts] Improving on basic L1 timing

2016-06-14 Thread Michael Wouters

Hello Angus

If you have 3 rubidiums of similar stability + 3 counters, you could
do a 3-cornered hat.

Otherwise, GPS common view to a better clock may be an option. If you
are reasonably close to a national standards lab, you might be able to
use their time-transfer files to compare your rubidiums with their
time scale - not everyone makes them publically available though.
Otherwise, if there is an IGS station near you, you could use the
station RINEX files and IGS clock solutions which are freely
available. Many IGS stations have a H-maser as the local clock. But it
may be just as good to simply use the comparison with GPS time
inherent in the time-transfer file.

The advantage of generating a time-transfer file is the possibility of
then improving upon the various corrections broadcast by GPS,
effectively repeating what the GPS receiver does to generate its
realization of GPS time but with better data.

With post-processing, the short to medium term (less than 1 day)
performance  can be improved a bit as you are suggesting when you
referred to "atmospheric issues". Improved ionospheric models are
available  or if there is an IGS station nearby, for example, the
measured ionosphere could be used. Other improvements can be had with
good antenna coordinates and using final orbits in the processing.

What can you use for your time-transfer receiver ? Some low-cost
single-frequency receivers are suitable eg the Trimble Resolution T.
The essential requirement is the availability of  raw code
measurements - with these you can generate CGGTTS time-transfer files
and/or RINEX observation files.

At least part of the software infrastructure to do this exists: the
OpenTTP project (www.openttp.org) has software for CGGTTS and RINEX
file generation for a few older,single frequency receivers, with
support for some other,current receivers under active development.
There is other software around, but it is orientated towards dual
frequency receivers and carrier phase processing.

Although it would be relatively straightforward to hack in use of
improved ionosphere, using final orbits is a bit harder since these
are not parameterized the same way as the broadcast orbits. Maybe
someone on time-nuts has software to do the conversion (and this would
have to be hacked into the OpenTTP software, rather than the final
time comparison).

The sort of performance you get on a zero baseline is a TDEV of a few
ns - you can extrapolate frequency stability from that.
On a 1000 km baseline, you can compare two Cs to better than 1 part in
10^13 @ 1 day.

All of the above is software-oriented, whereas you seem to be looking
for a hardware solution, but that's what I know best.

Cheers
Michael

On Tue, Jun 14, 2016 at 6:16 PM, Angus  wrote:
> Hi,
>
> I'm planning to test some rubidiums again, but since Santa never did
> get me that hydrogen maser I asked for, I'm still stuck with ordinary
> gps timing receivers as a separate medium to long term reference. The
> atmospheric issues are probably the main ones I would like to get rid
> of, although the more errors removed the better.
>
> It does not have to be done in real time, but even an single test run
> would last weeks, so there could be a lot of data to tie together.
>
> It would really need to be something that actually exists rather than
> just an idea of how it might be done, since I really just don't have
> time for any more major projects anytime soon. I've found from
> experience that too much time spent making the test gear etc means
> that I don't get the time to actually use it!
>
> I'm also looking for something that's not too expensive - like up to
> hundreds rather than thousands of pounds.
> A good cesium or 2+ frequency gps with relevant options might be fine,
> but also rather out of my price range.
>
> BTW, I do plan on uploading the end results, in case anyone is
> interested.
>
>
> If anyone knows of some way to do this, (or even has something
> appropriate they want to sell) I'd appreciate hearing about it, on or
> off-list.
>
> Thanks,
> Angus.
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Re: [time-nuts] DIY TimePod

Hi

The input to the ADC is lowpass filtered. If you use a square wave it “sees” a 
more or less sine wave. If you are running
a very low frequency square wave, you can use an external lowpass filter. Since 
one channel is a reference, you may only 
need one external lowpass filter. 

Bob

> On Jun 14, 2016, at 3:35 AM, John Swenson  wrote:
> 
> The idea here is around a 80MHz sample clock with a maximum input/ref signal 
> of around 25MHz. This is based on the TimePod with ADCs, which is supposed to 
> work with square waves. Its is using a 77MHz clock if I remember correctly, 
> so somewhere in the neighborhood of 12-13 ns per sample.
> 
> When you feed a square wave into this you have several samples at say 50, 
> then it jumps to 50,000 stays there for several samples, then jumps down to 
> 50 again. This still seems like a binary sample. The difference is that every 
> now and then the sample hits during a ramptime of the square wave and will 
> give some intermediate value, is this enough of a difference to invalidate 
> the concept of a binary sample?
> 
> Or is the difference that the ADC won't stay at 50, but will be bouncing 
> around say between 45 and 55 when the square wave is low and this noise makes 
> it work? If that is the case then wouldn't a longer measurement time do 
> essentially the same thing with slight variations of timing of the edge due 
> to the noise in the binary sampler?
> 
> John S.
> 
> 
> On 6/13/2016 8:17 PM, Chris Caudle wrote:
>> On Mon, June 13, 2016 9:38 pm, Bruce Griffiths wrote:
>>> If the quantisation noise is random and spread uniformly over the Nyquist
>>> bandwidth (~40MHz??) then the noise floor is about -82dBc/Hz.
>> 
>> How do you spread the quantization noise randomly with a one bit
>> quantizer?  I'm mostly familiar with single bit quanitizers in the context
>> of audio range delta-sigma converters where the quantizer is in a feedback
>> loop to move most of the noise to a higher frequency range. That also
>> requires a clock much higher than the minimum nyquist requirement.
>> 
>> Maybe I need to see a block diagram of what is being described.  Where is
>> the clock for the ECL flip-flop generated?  I don't recall seeing a
>> description of what the effective sample rate will be, or the highest
>> clock signal accepted for analysis.
>> 
>>> With a high resolution RF ADC internal noise is usually sufficient
>>> (>= 1 lsb)) to ensure this.
>> 
>> Can't really dither to >= 1lsb when lsb=msb (single bit quantizer).
>> 
> 
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Re: [time-nuts] DIY TimePod