Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-03 Thread Ulrich Bangert
For a lot of people the FFT seems to be the "one size fits all" solution to
any frequency and phase related problem in DSP. It is NOT! For
frequency/phase detection & comparisons from sets of sampled data the
methods explained in

http://ipnpr.jpl.nasa.gov/progress_report/42-121/121G.pdf

are MUCH more appropiate.

Best regards
Ulrich Bangert

> -Ursprungliche Nachricht-
> Von: time-nuts-boun...@febo.com 
> [mailto:time-nuts-boun...@febo.com] Im Auftrag von Hal Murray
> Gesendet: Mittwoch, 3. Juni 2009 20:00
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] Sound Cards for locking to GPSDO 10 
> MHz references
> 
> 
> 
> > One of the main problems is that in working at milli-Hz 
> binwidths the 
> > FTT word length needs to be very long to cover even a few 
> tens of Hz 
> > range and we run into memory problems.
> 
> I'm missing something.  How much memory do you have on your laptop?
> 
> I'm not a DSP wizard.  If you have 10 Hz bandwidth and you 
> want milli-Hz 
> bins, that takes 2x10x1000 samples.  Right?  I'd expect that 
> to fit easily.
> 
> That's 20K samples, at 8 bytes each, round up to 10, call it 
> 200K bytes.
> 
> Jumping to micro-Hz might get interesting.  That would be 200 
> megabytes.  
> Lots of laptops have room for that.  Maybe not an old one.
> 
> Even with an old laptop without much memory, I'd expect you 
> could do several 
> factors of 2 better than milli-Hz bins.
> 
> On the other hand, how much bandwidth do you really need?  
> Junk crystals are 
> 50-100 ppm.  100 ppm at 1 KHz is 1/10 Hz.  So why do you need 
> more than 1 Hz 
> input bandwidth?  You can probably get closer than that by 
> calibrating the 
> crystals in your particular gear.
> 
> Connie's numbers were 250 micro-Hz drift with a 500 micro-Hz 
> offset.  (That 
> was with reasonably stable temperature.)  So a few milli-Hz 
> bandwidth looks 
> like enough.
> 
> 
> 
> 
> 
> -- 
> These are my opinions, not necessarily my employer's.  I hate spam.
> 
> 
> 
> 
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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-03 Thread Connie Marshall
You know, I probably need to run the test again and do a better job of
tracking room temp. My thermometer is high up on the wall in the shack. The
computer sets under the bench in a corner. It does represent a typical
afternoon in my shack however.

73,

Connie
K5CM


-Original Message-
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on
Behalf Of Hal Murray
Sent: Wednesday, June 03, 2009 12:24 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz
references



connie.marsh...@suddenlink.net said:
> www.k5cm.com/soundcard.htm

Nice, thanks.

>From there:
> Sound card drift over this four hour period is about 250 micro Hertz.
> The temp in the shack was going up during the measurement period.
> Unfortunately I did not track the exact temp rise, but was about
> around 4 to 6 degrees F.

250 micro Hz relative to 1000 Hz is 1/4 ppm.

My memory is that junk PC crystals are ballpark of 1 ppm/degree.  (That's
probably per degree C rather than F, but that's only a factor of 2.)

So 1/4 ppm for 4 degrees is better than I would have guessed.


--
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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-03 Thread Hal Murray
> There is an overbeleif in what software is suitable for IMHO.

[Fun discussion.  Thanks.]

Many years ago, somebody on the FPGA newsgroup pointed out that, in general, 
if you can do the problem in software that's probably the better way.  One of 
the considerations is that it's easier to hire programmers rather than 
hardware designers.

FPGAs are halfway between real hardware and software.  You can try a simple 
change without any harsh time or cost penalty to make new masks and new 
chips.  If that change is a bug fix, you might think of it as typical sloppy 
programmer behavior.  On the other hand, that change may be a new idea you 
want to try...


For many people in this group, fun is probably the most important 
consideration.  Different things will appeal to different people.



-- 
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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-03 Thread Hal Murray

> One of the main problems is that in working at milli-Hz binwidths the
> FTT word length needs to be very long to cover even a few tens of Hz
> range and we run into memory problems.

I'm missing something.  How much memory do you have on your laptop?

I'm not a DSP wizard.  If you have 10 Hz bandwidth and you want milli-Hz 
bins, that takes 2x10x1000 samples.  Right?  I'd expect that to fit easily.

That's 20K samples, at 8 bytes each, round up to 10, call it 200K bytes.

Jumping to micro-Hz might get interesting.  That would be 200 megabytes.  
Lots of laptops have room for that.  Maybe not an old one.

Even with an old laptop without much memory, I'd expect you could do several 
factors of 2 better than milli-Hz bins.

On the other hand, how much bandwidth do you really need?  Junk crystals are 
50-100 ppm.  100 ppm at 1 KHz is 1/10 Hz.  So why do you need more than 1 Hz 
input bandwidth?  You can probably get closer than that by calibrating the 
crystals in your particular gear.

Connie's numbers were 250 micro-Hz drift with a 500 micro-Hz offset.  (That 
was with reasonably stable temperature.)  So a few milli-Hz bandwidth looks 
like enough.





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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-03 Thread Hal Murray

connie.marsh...@suddenlink.net said:
> www.k5cm.com/soundcard.htm

Nice, thanks.

>From there:
> Sound card drift over this four hour period is about 250 micro Hertz.
> The temp in the shack was going up during the measurement period.
> Unfortunately I did not track the exact temp rise, but was about
> around 4 to 6 degrees F.

250 micro Hz relative to 1000 Hz is 1/4 ppm.

My memory is that junk PC crystals are ballpark of 1 ppm/degree.  (That's 
probably per degree C rather than F, but that's only a factor of 2.)

So 1/4 ppm for 4 degrees is better than I would have guessed.


-- 
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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-03 Thread Magnus Danielson

Lux, James P skrev:

-Original Message-
From: time-nuts-boun...@febo.com 
[mailto:time-nuts-boun...@febo.com] On Behalf Of Rex Moncur

Sent: Tuesday, June 02, 2009 3:06 PM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] Sound Cards for locking to GPSDO 10 
MHz references


Hi all

Thank you all for you advice and suggestions re my request.  
At this stage it does not look like there is a simple 
solution of a readily available USB sound card that can be 
locked to a 10 MHz GPSDO reference.


The constraints of portable operation with a Laptop rule out 
a number of solutions.  I have tried the software solution 
using Spectrum Lab but ran into problems and perhaps this 
just needs more work.  One of the main problems is that in 
working at milli-Hz binwidths the FTT word length needs to be 
very long to cover even a few tens of Hz range and we run 
into memory problems. So there is little room to have a 
reference frequency spaced well away from the frequency range 
being used.


The reference frequency can be right on top of your signal, as long as it's 
within the dynamic range. You can subtract it out before doing the FFT, after 
having determined where it is and how big it is.


Considering the length of these traces, the local oscillator vs. the 
reference will shift around.


What I would do is to ensure that the reference signal and input signal 
is either on very different frequencies or different channels.


Then, I would in the sampling phase frequency convert the receive signal 
and reference signal using digital fixed NCO/quadrature oscillators 
(cos, sin) and do integrate and dump (synchronous dump for both receive 
and reference signals) processing for low pass filtering and reducing 
sample rate. Since the signal was fairly narrow banded, this digital 
receiver approach would significantly reduce the amounts of data while 
requiring a very reasonable amount of real-time processing.


The remaining sample stream still contains the crutial information if 
sufficient bandwidth is maintained after the integrate and dump processing.


Cheers,
Magnus

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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-03 Thread Magnus Danielson

Alberto di Bene skrev:

Magnus Danielson wrote:


Hmm, do you get a feeling that I am actually object very much to just 
toss it into the processor. I think you are right. :)


I suppose you are familiar with the old American adage that says that to 
a man with

a hammer every problem looks like a nail :-)


Yes. :o)

Each of us is more familiar with one or another technology (broadly 
speaking), and tend to see it as the best way to solve problems. I am not immune 
from this...


This is why I try to find more tools and more approaches.

Nothing wrong with software, but use it wisely. Build the test-benches 
as if you where doing a ASIC or full-custom design and thus also think 
about each compile costing you milions of dollars and a pipe-line 
depth of many months (6-9).


Given the rate of compiles that sometimes I do especially when near to 
find the solution of a problem that bugged me for a long time, I would be bankrupted
since long, should each compile cycle cost me thousands or millions of 
dollars, even if bogus dollars... :-) :-)


I think you would learn important lessons in test-benching and overall 
design before the "compile".


I guess I am becomming more conservative by the day. From my own and 
others mistakes and succsesses.


This is a privilege of becoming older and wiser :-)


Whiee... I got so much to learn then! :)

Cheers,
Magnus

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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-02 Thread Connie Marshall

Hi Rex,

Here is a plot of my sound card. Maybe I'm just lucky with this particular
sound card/computer, but the drift was only about 250 micro Hertz over a
four hour period. Also for critical measurements I try to run at 200 Hz
center frequency rather than 1000 Hz. Cuts the error by five. Maybe that's
not practical for you modulation schema.

I did not bother to calibrate the sound card before I started the test so
there is about 550 micro Hertz of static error when the test starts.

www.k5cm.com/soundcard.htm

73,

Connie
K5CM


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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-02 Thread Lux, James P
> -Original Message-
> From: time-nuts-boun...@febo.com 
> [mailto:time-nuts-boun...@febo.com] On Behalf Of Rex Moncur
> Sent: Tuesday, June 02, 2009 3:06 PM
> To: 'Discussion of precise time and frequency measurement'
> Subject: Re: [time-nuts] Sound Cards for locking to GPSDO 10 
> MHz references
> 
> Hi all
> 
> Thank you all for you advice and suggestions re my request.  
> At this stage it does not look like there is a simple 
> solution of a readily available USB sound card that can be 
> locked to a 10 MHz GPSDO reference.
> 
> The constraints of portable operation with a Laptop rule out 
> a number of solutions.  I have tried the software solution 
> using Spectrum Lab but ran into problems and perhaps this 
> just needs more work.  One of the main problems is that in 
> working at milli-Hz binwidths the FTT word length needs to be 
> very long to cover even a few tens of Hz range and we run 
> into memory problems. So there is little room to have a 
> reference frequency spaced well away from the frequency range 
> being used.

The reference frequency can be right on top of your signal, as long as it's 
within the dynamic range. You can subtract it out before doing the FFT, after 
having determined where it is and how big it is.

> Some people asked for more details of the cloud scatter 
> experiments which area at http://reast.asn.au/optical.php  
> There is also a series of articles on our work in the last 3 
> and next issue of DUBUS.
> 
>
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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-02 Thread Rex Moncur
Hi all

Thank you all for you advice and suggestions re my request.  At this stage
it does not look like there is a simple solution of a readily available USB
sound card that can be locked to a 10 MHz GPSDO reference.

The constraints of portable operation with a Laptop rule out a number of
solutions.  I have tried the software solution using Spectrum Lab but ran
into problems and perhaps this just needs more work.  One of the main
problems is that in working at milli-Hz binwidths the FTT word length needs
to be very long to cover even a few tens of Hz range and we run into memory
problems. So there is little room to have a reference frequency spaced well
away from the frequency range being used.

The SP DIF solution seems promising if I can generate the required input.
This could perhaps be done with a product that already provides the SP DIF
word output and locking that.  But that could be just as hard as locking the
sound-card in the first place.

So at this time I think I will put some more effort into locking the sound
card and let you know how I go, hi. Injection locking as suggested by some
of you may be the answer.

Some people asked for more details of the cloud scatter experiments which
area at http://reast.asn.au/optical.php  There is also a series of articles
on our work in the last 3 and next issue of DUBUS.

On the question of Doppler shift from clouds - this is much less than a mHz
and not an issue due to the fact that we are using base band and the Doppler
only applies to the audio frequency.  In addition the very narrow beamwidths
(around 2 degrees) mean that the possible paths are all very similar in
length.


Thanks again to everyone for their input.

73 Rex VK7MO


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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-02 Thread Alberto di Bene

Magnus Danielson wrote:


Hmm, do you get a feeling that I am actually object very much to just 
toss it into the processor. I think you are right. :)


I suppose you are familiar with the old American adage that says that to a man 
with
a hammer every problem looks like a nail :-)

Each of us is more familiar with one or another technology (broadly speaking),
and tend to see it as the best way to solve problems. I am not immune from 
this...

Nothing wrong with software, but use it wisely. Build the test-benches 
as if you where doing a ASIC or full-custom design and thus also think 
about each compile costing you milions of dollars and a pipe-line depth 
of many months (6-9).


Given the rate of compiles that sometimes I do especially when near to find the
solution of a problem that bugged me for a long time, I would be bankrupted
since long, should each compile cycle cost me thousands or millions of dollars,
even if bogus dollars... :-) :-)

I guess I am becomming more conservative by the day. From my own and 
others mistakes and succsesses.


This is a privilege of becoming older and wiser :-)

Cheers,
Alberto  I2PHD



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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-02 Thread Magnus Danielson

Alberto di Bene skrev:

Magnus Danielson wrote:



No need to switch on the soldering iron...
Never do in hardware what can be done in software :-)


Respectfully I disagree. There are tasks which is better managed by 
software and tasks which is better managed by hardware. In the world 
of FPGAs, it is also worth mentioning that some tasks is best done there.
The big trick is to find a balance between various methods, available 
resources, partitioning of the problem, doing it on time and achieving 
the needed performance.




Of course you are right, the best solution must be decided case by case.
But the biggest plus of the software is that it can be changed on the fly,
without an expensive reworking station, and the manual ability to correctly
use it.  And a side effect is speed : you can test many variants of a 
solution
in a time frame of a few minutes.  Not so easily doable with hardware 
changes.


This is why we do alot of things in FPGAs today, and in the FPGAs we 
often put dedicated DSPs of various complexity, often adapted to their 
task. Keeping quick turn-around is on our mind, but in general, the 
shorter turn-around, the poorer testing usually happends, and the 
sloopier design is often found, and the longer it takes to get the job done.


In general, a CPU is suitable for doing non-common tasks. More dedicated 
designs like firmware and hardware is suitable to do things which is 
essentially the same but happends over and over and over and often at a 
 high speed. Such monotonic tasks just waste energy, space and 
complexity when done in CPUs. The problem with a generic CPU is that it 
is generic, so it can do all kinds of tasks, which makes timing-critical 
bulk-processing tasks problematic to combine with sporadic and possibly 
high-dynamic processing. Splice the bulk off to some dedicated 
processing, which can be done in another CPU, and better performance is 
yielded. There are loads of designs where a few well thought 8-bit 
processors work together and shine over a more modern fancy design.


One such example is found in the SR-620 which has a Zilog Z-8000 
processor as main CPU and a Z-80 co-processor which only does the X-Y 
vector display. The Z-80 has so small program that it is loaded into 
SRAM from the Z-8000 as it boots.


The HP 5334A has actually 3 different 3870 processor, one for overall 
control, one for measurements and one for GPIB.


Hmm, do you get a feeling that I am actually object very much to just 
toss it into the processor. I think you are right. :)
Nothing wrong with software, but use it wisely. Build the test-benches 
as if you where doing a ASIC or full-custom design and thus also think 
about each compile costing you milions of dollars and a pipe-line depth 
of many months (6-9).


I guess I am becomming more conservative by the day. From my own and 
others mistakes and succsesses.


Cheers,
Magnus

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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-02 Thread Alberto di Bene

Magnus Danielson wrote:



No need to switch on the soldering iron...
Never do in hardware what can be done in software :-)


Respectfully I disagree. There are tasks which is better managed by 
software and tasks which is better managed by hardware. In the world of 
FPGAs, it is also worth mentioning that some tasks is best done there.
The big trick is to find a balance between various methods, available 
resources, partitioning of the problem, doing it on time and achieving 
the needed performance.




Of course you are right, the best solution must be decided case by case.
But the biggest plus of the software is that it can be changed on the fly,
without an expensive reworking station, and the manual ability to correctly
use it.  And a side effect is speed : you can test many variants of a solution
in a time frame of a few minutes.  Not so easily doable with hardware changes.

73  Alberto  i2PHD


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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-02 Thread Magnus Danielson

Alberto di Bene skrev:

J.D. Bakker wrote:
You could always transform this from a hardware problem to a software 
problem. Take the output of your GPSDO, divide it down to somewhere 
inside the audio band, feed it to a spare input on your USB sound card 
and have software track this reference and correct the received signal.


JDB.


I am in complete agreement with this kind of solution. Sampling on the
second channel a reference signal of known value allows the software
to make a simple adjustment.


Such a double-frequency conversion cancels fairly well the transfer 
oscillators frequency and jitter, as long as it is sufficienly low.



No need to switch on the soldering iron...
Never do in hardware what can be done in software :-)


Respectfully I disagree. There are tasks which is better managed by 
software and tasks which is better managed by hardware. In the world of 
FPGAs, it is also worth mentioning that some tasks is best done there.
The big trick is to find a balance between various methods, available 
resources, partitioning of the problem, doing it on time and achieving 
the needed performance.


There is an overbeleif in what software is suitable for IMHO.

Cheers,
Magnus

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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-02 Thread Magnus Danielson

Lux, James P skrev:

-Original Message-
From: time-nuts-boun...@febo.com 
[mailto:time-nuts-boun...@febo.com] On Behalf Of Magnus Danielson

Sent: Tuesday, June 02, 2009 10:08 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Sound Cards for locking to GPSDO 10 
MHz references




Some of the "pro" sound interfaces have a "word clock" input.  

There are a variety of things that take a external input 
and generate a S/PDIF that's properly timed, as well. Lots of 
boxes will take a S/PDIF sync input (e.g. the Edirol FA-66 
which was used by lots of Flex-Radio folk), so maybe that's 
something you could easily generate from your 10MHz. 
A chart at Cakewalk shows that MOTU has a USB interface (828MkII) 
which has a word clock sync. It's going to be a pricey 
beast though, 

with 8in/8out ($800?)

Even if you have a word clock input, you're going to have to 
synthesize that from the 10 MHz.  Maybe it's easier to just make a 
S/PDIF which is a MUCH more common sync signal. ( I think S/PDIF is 
something like 3 MHz)
S/P-DIF [iec60958-3] has a baudrate which is 128 x sample 
rate and a bit rate which is 64 x sample rate, which is 
inherited properties from AES/EBU [aes3] [tech3250] [iec60958-4].


Locking up a S/P-DIF (128 x sample rate) is about the same 
job as locking up a superclock (256 x sample rate) or 
wordclock (1 x sample rate).


However, if you're buying an off the shelf audio interface, you're
stuck with whatever the mfr is providing for a sync input, and a
(very) casual inspection of what's available these days
(particularly at low cost) shows that S/PDIF seems to be the most common.


Do they really lock up to the S/P-DIF input? I doubt it for the cheap 
boards. Rather, they decode the S/P-DIF signal and ship the samples into 
the DSP. The DSP tends to make very rought sample-rate conversions like 
dropping samples etc.


A lockable board isn't that expensive. You can get them off ebay for 
instance.


Cheers,
Magnus

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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-02 Thread Stan W1LE

Hello The Net:

For portable operations with a laptop, usually only one input channel is 
available

and it is at mike (not line) level.

The alternative to sum the analog reference and the analog signal of 
interest may be
possible if the reference noise can be kept out of the signal of 
interest bandwidth.
Maybe a external USB soundcard with at least 2 input channels is more 
appropriate.


Stan, W1LEFN41sr Cape Cod


Alberto di Bene wrote:

J.D. Bakker wrote:
You could always transform this from a hardware problem to a software 
problem. Take the output of your GPSDO, divide it down to somewhere 
inside the audio band, feed it to a spare input on your USB sound 
card and have software track this reference and correct the received 
signal.


JDB.


I am in complete agreement with this kind of solution. Sampling on the
second channel a reference signal of known value allows the software
to make a simple adjustment. No need to switch on the soldering iron...
Never do in hardware what can be done in software :-)

73  Alberto  I2PHD



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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-02 Thread Alberto di Bene

J.D. Bakker wrote:
You could always transform this from a hardware problem to a software 
problem. Take the output of your GPSDO, divide it down to somewhere 
inside the audio band, feed it to a spare input on your USB sound 
card and have software track this reference and correct the received 
signal.


JDB.


I am in complete agreement with this kind of solution. Sampling on the
second channel a reference signal of known value allows the software
to make a simple adjustment. No need to switch on the soldering iron...
Never do in hardware what can be done in software :-)

73  Alberto  I2PHD


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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-02 Thread Lux, James P
> -Original Message-
> From: time-nuts-boun...@febo.com 
> [mailto:time-nuts-boun...@febo.com] On Behalf Of Magnus Danielson
> Sent: Tuesday, June 02, 2009 10:08 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Sound Cards for locking to GPSDO 10 
> MHz references
> 
> > 
> > 
> > Some of the "pro" sound interfaces have a "word clock" input.  
> > 
> > There are a variety of things that take a external input 
> and generate a S/PDIF that's properly timed, as well. Lots of 
> boxes will take a S/PDIF sync input (e.g. the Edirol FA-66 
> which was used by lots of Flex-Radio folk), so maybe that's 
> something you could easily generate from your 10MHz. 
> > 
> > A chart at Cakewalk shows that MOTU has a USB interface (828MkII) 
> > which has a word clock sync. It's going to be a pricey 
> beast though, 
> > with 8in/8out ($800?)
> > 
> > Even if you have a word clock input, you're going to have to 
> > synthesize that from the 10 MHz.  Maybe it's easier to just make a 
> > S/PDIF which is a MUCH more common sync signal. ( I think S/PDIF is 
> > something like 3 MHz)
> 
> S/P-DIF [iec60958-3] has a baudrate which is 128 x sample 
> rate and a bit rate which is 64 x sample rate, which is 
> inherited properties from AES/EBU [aes3] [tech3250] [iec60958-4].
> 
> Locking up a S/P-DIF (128 x sample rate) is about the same 
> job as locking up a superclock (256 x sample rate) or 
> wordclock (1 x sample rate).

However, if you're buying an off the shelf audio interface, you're stuck with 
whatever the mfr is providing for a sync input, and a (very) casual inspection 
of what's available these days (particularly at low cost) shows that S/PDIF 
seems to be the most common.


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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-02 Thread Magnus Danielson

Lux, James P skrev:

-Original Message-
From: time-nuts-boun...@febo.com 
[mailto:time-nuts-boun...@febo.com] On Behalf Of Rex Moncur

Sent: Monday, June 01, 2009 3:00 PM
To: 'Discussion of precise time and frequency measurement'
Subject: [time-nuts] Sound Cards for locking to GPSDO 10 MHz 
references


 
Hi all 

Does anyone have any experience of locking a USB external 
soundcard to a GPSDO 10 MHz reference.


I am interested in advice on any good quality soundcards that 
can be readily locked to either 10 MHz or if necessary to 
some other frequency that we can derive from a GPSDO source.  
I have done some tests with the SignalLink soundcard that 
uses a Texas Instruments PCM2904 chip and requires a 12 MHz 
lock frequency.  This requires some cutting of tracks to 
remove the internal oscillator feedback and insert the 
locking frequency.  12 MHz is readily derived from 10 MHz but 
I have not been able to get it to lock.  The Texas 
instruments data sheet suggests that it is possible to use an 
external refernce but also says this is not recommended.  
With this expereicne I would rather find a sound card that is 
designed for external locking that does not require the 
cutting of tracks.


For info the purpose of this request is that we are looking 
at using very narrow bandwidth modes at less than 1 mHz for 
light wave communcation.  To date using LEDs and cloud 
reflection we have worked over 200 km with WSJT but we should 
be able to do 20 dB better if we can get down to milli-Hz 
bandwidths (at the expense of spending all night to complete 
a QSO). Our expereince to date is that standard sound cards 
are just not stable to better than 5 milli-Hz at 1000 Hz 
which should be readily solved by GPS locking let us get down 
to sub milli-Hz levels.


Rex VK7MO



Some of the "pro" sound interfaces have a "word clock" input.  

There are a variety of things that take a external input and generate a S/PDIF that's properly timed, as well. Lots of boxes will take a S/PDIF sync input (e.g. the Edirol FA-66 which was used by lots of Flex-Radio folk), so maybe that's something you could easily generate from your 10MHz. 


A chart at Cakewalk shows that MOTU has a USB interface (828MkII) which has a 
word clock sync. It's going to be a pricey beast though, with 8in/8out ($800?)

Even if you have a word clock input, you're going to have to
synthesize that from the 10 MHz.  Maybe it's easier to just
make a S/PDIF which is a MUCH more common sync signal. ( I
think S/PDIF is something like 3 MHz)


S/P-DIF [iec60958-3] has a baudrate which is 128 x sample rate and a bit 
rate which is 64 x sample rate, which is inherited properties from 
AES/EBU [aes3] [tech3250] [iec60958-4].


Locking up a S/P-DIF (128 x sample rate) is about the same job as 
locking up a superclock (256 x sample rate) or wordclock (1 x sample rate).


As long as the signal is samples with low jitter and A/D converted in a 
good fashion, delivery over S/P-DIF should not be too hard. An ADC is 
slammed onto a AES/EBU/S/P-DIF chip which is fairly trivial extra work.


Cheers,
Magnus

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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-02 Thread J.D. Bakker
You could always transform this from a hardware problem to a software 
problem. Take the output of your GPSDO, divide it down to somewhere 
inside the audio band, feed it to a spare input on your USB sound 
card and have software track this reference and correct the received 
signal.


JDB.
--
LART. 250 MIPS under one Watt. Free hardware design files.
http://www.lartmaker.nl/

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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-02 Thread Magnus Danielson

Brian Kirby skrev:
I use a Lynx One sound card, it has analog and digital I/O and MIDI I/O 
and clock I/O.  Their manuals are available on line at 
www.lynxstudio.com.  These are profession 24 bit cards, the analog I/O 
uses balanced interfaces.  They handle AES/EBU and SP DIF digital audio 
formats.


The sound card can take an internal clock, an external clock input on 
the MIDI port, there is a parallel clock header on the PC board, and a 
digital clock input on the digital audio lines.


It can accept a 13.5 Mhz video dot clock, a 27 Mhz video dot clock, and 
a word clock and word clock/256.


13,5 MHz is ITU-R BT.601/BT.656 luminance sampling rate.
27 MHz is BT.601/BT.656 luminance/chroma-difference combined sampling 
rate (4:2:2).


27 MHz is the video reference rate of them all. Sad that they broke it 
when they did the North American HD stuff. Breaking numerology like that 
isn't very nice... it always cost extra now.


I think you mean word-clock * 256 as this is Digidesign/ProTools clock 
distribution strategy, giving 12,288 MHz for 48 kHz sampling rate.


Cheers,
Magnus

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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-01 Thread Brian Kirby
I use a Lynx One sound card, it has analog and digital I/O and MIDI I/O 
and clock I/O.  Their manuals are available on line at 
www.lynxstudio.com.  These are profession 24 bit cards, the analog I/O 
uses balanced interfaces.  They handle AES/EBU and SP DIF digital audio 
formats.


The sound card can take an internal clock, an external clock input on 
the MIDI port, there is a parallel clock header on the PC board, and a 
digital clock input on the digital audio lines.


It can accept a 13.5 Mhz video dot clock, a 27 Mhz video dot clock, and 
a word clock and word clock/256.


It can also take a single source frequency as a referenve clock.

Its basicaly set up to sync and slave SMPTE timing systems

Hope that helped..

Rex Moncur wrote:
 
Hi all 


Does anyone have any experience of locking a USB external soundcard to a
GPSDO 10 MHz reference.

I am interested in advice on any good quality soundcards that can be readily
locked to either 10 MHz or if necessary to some other frequency that we can
derive from a GPSDO source.  I have done some tests with the SignalLink
soundcard that uses a Texas Instruments PCM2904 chip and requires a 12 MHz
lock frequency.  This requires some cutting of tracks to remove the internal
oscillator feedback and insert the locking frequency.  12 MHz is readily
derived from 10 MHz but I have not been able to get it to lock.  The Texas
instruments data sheet suggests that it is possible to use an external
refernce but also says this is not recommended.  With this expereicne I
would rather find a sound card that is designed for external locking that
does not require the cutting of tracks.

For info the purpose of this request is that we are looking at using very
narrow bandwidth modes at less than 1 mHz for light wave communcation.  To
date using LEDs and cloud reflection we have worked over 200 km with WSJT
but we should be able to do 20 dB better if we can get down to milli-Hz
bandwidths (at the expense of spending all night to complete a QSO). Our
expereince to date is that standard sound cards are just not stable to
better than 5 milli-Hz at 1000 Hz which should be readily solved by GPS
locking let us get down to sub milli-Hz levels.

Rex VK7MO


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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-01 Thread Lux, James P

> -Original Message-
> From: time-nuts-boun...@febo.com 
> [mailto:time-nuts-boun...@febo.com] On Behalf Of Rex Moncur
> Sent: Monday, June 01, 2009 3:00 PM
> To: 'Discussion of precise time and frequency measurement'
> Subject: [time-nuts] Sound Cards for locking to GPSDO 10 MHz 
> references
> 
>  
> Hi all 
> 
> Does anyone have any experience of locking a USB external 
> soundcard to a GPSDO 10 MHz reference.
> 
> I am interested in advice on any good quality soundcards that 
> can be readily locked to either 10 MHz or if necessary to 
> some other frequency that we can derive from a GPSDO source.  
> I have done some tests with the SignalLink soundcard that 
> uses a Texas Instruments PCM2904 chip and requires a 12 MHz 
> lock frequency.  This requires some cutting of tracks to 
> remove the internal oscillator feedback and insert the 
> locking frequency.  12 MHz is readily derived from 10 MHz but 
> I have not been able to get it to lock.  The Texas 
> instruments data sheet suggests that it is possible to use an 
> external refernce but also says this is not recommended.  
> With this expereicne I would rather find a sound card that is 
> designed for external locking that does not require the 
> cutting of tracks.
> 
> For info the purpose of this request is that we are looking 
> at using very narrow bandwidth modes at less than 1 mHz for 
> light wave communcation.  To date using LEDs and cloud 
> reflection we have worked over 200 km with WSJT but we should 
> be able to do 20 dB better if we can get down to milli-Hz 
> bandwidths (at the expense of spending all night to complete 
> a QSO). Our expereince to date is that standard sound cards 
> are just not stable to better than 5 milli-Hz at 1000 Hz 
> which should be readily solved by GPS locking let us get down 
> to sub milli-Hz levels.
> 
> Rex VK7MO


Some of the "pro" sound interfaces have a "word clock" input.  

There are a variety of things that take a external input and generate a S/PDIF 
that's properly timed, as well. Lots of boxes will take a S/PDIF sync input 
(e.g. the Edirol FA-66 which was used by lots of Flex-Radio folk), so maybe 
that's something you could easily generate from your 10MHz. 

A chart at Cakewalk shows that MOTU has a USB interface (828MkII) which has a 
word clock sync. It's going to be a pricey beast though, with 8in/8out ($800?)

Even if you have a word clock input, you're going to have to synthesize that 
from the 10 MHz.  Maybe it's easier to just make a S/PDIF which is a MUCH more 
common sync signal. ( I think S/PDIF is something like 3 MHz)

The HPSDR folks also might have something...
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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-01 Thread John Miles
The concern I'd have with modifying a USB sound card, or any of them for
that matter, is that the glue logic between the ADC and the USB chip may be
designed for a certain relationship between the ADC and USB clocks.  Running
the ADC asynchronously may or may not be robust depending on the assumptions
baked into the gate array.  It might be OK if your app can tolerate
occasional misclocking or dropouts but I'd be reluctant to use a hacked
sound card for anything timing-critical.

I just (last week) got an AD7760 ADC eval board working with the Digilent
Nexys2 FPGA platform, with the EVAL-AD7760 board running from its own 40 MHz
clock.  It will accept an external 40 MHz clock source that, in turn,
wouldn't be hard to derive from 10 MHz.  Way overkill for ultra
low-bandwidth work, but if anyone is looking for a clean digitizer for audio
rates in general, you could do a lot worse than this approach.  Cost isn't
too bad either, at $130 for the Nexys2 and $150 for the ADC7760 eval board.
Of course the big drawback is the lack of any sort of standardized audio
driver on the host side.

If/when I spin a PCB for this project I'll definitely include a 10 MHz
input.

-- john, KE5FX


> -Original Message-
> From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on
> Behalf Of Jeffrey Pawlan
> Sent: Monday, June 01, 2009 3:08 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz
> references
>
>
> Soundcards for USB are poor at best.
>
> I have a set of PCI cards that were previously made by EMU and
> they accept
> external reference input.  They no longer make the model I have
> but perhaps
> they have another PCI card with an external ref input.
>
> I am interested in your modulation technique which allows you to use WSJT.
> Please let me know exactly what you are doing. I also do not know
> how you are
> using 5 milliHertz with WSJT since the group of discrete tones
> occupy more
> bandwidth.
>



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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-01 Thread Hal Murray

rmon...@bigpond.net.au said:
> For info the purpose of this request is that we are looking at using
> very narrow bandwidth modes at less than 1 mHz for light wave
> communcation.  To date using LEDs and cloud reflection we have worked
> over 200 km with WSJT but we should be able to do 20 dB better if we
> can get down to milli-Hz bandwidths (at the expense of spending all
> night to complete a QSO). Our expereince to date is that standard
> sound cards are just not stable to better than 5 milli-Hz at 1000 Hz
> which should be readily solved by GPS locking let us get down to sub
> milli-Hz levels. 

Sounds like a fun project.

Do the clouds shift around enough to cause Doppler problems?

You might find something in the way of a DSP or FPGA demo board.  (I don't 
have any suggestions.)  Or maybe a demo board for an audio chip.

How stable is the osc on your current board?  Do you need accuracy or 
stability?

Can you feed a calibration signal in the other stereo channel and sort it out 
in software?

Or tap off some signal in the board and feed that to a counter for 
calibration.


-- 
These are my opinions, not necessarily my employer's.  I hate spam.




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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-01 Thread Rex Moncur
Hi Jeff

Thanks for your advice which I will follow up - the reason for going for a
USB sound card is that the system must be operated portable with a Laptop -
but perhaps there is a way to use a PCI sound card on a Laptop.

While we use WSJT at present we have a new Mode under development for the
mill-Hz bandwidth. In testing this new mode is acheiveing around 15 dB
better than WSJT with 5 mHz binwidths and should get to 20 dB better with 1
mHz binwidths. It uses M-ary FSK like WSJT but does not need a reference
tone for time or frequency locking on the basis that both soundcards are GPS
locked. Timing errors are not an issue as the tone durations are 16 mins at
1 mHz binwidth.  We use around 20,000 separate M-ary tones (cf 64 for WSJT),
which is sufficient to send the first three characters of a call sign in
Clark-Karn source encoded format - thus it requires only two tones to be
sent to receve a full callsign. However at one mHz bandwidth this takes 16
minutes to send a single tone and thus an hour to send two callsigns.
However, we have some shorter techniques for exchanging reports and RRR so a
QSO can be comppleted in around 3 hours, hi. We can fit 20,000 tones spaced
1 mHz apart into just 20 Hz so there is not problem there. We have not yet
added FEC which should allow a further improvement but we would like to
resolve the sound card stablity issues first.

73 Rex VK7MO 



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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-01 Thread Alan Melia
I have seen it talked about (around the LF fraternity, but generally they
are stable enough there and just need calibation) a lot but not accomplished
yet.

How about injection locking the on board oscmaybe gating the feedback
with the referencenote I havent tried this? Another technique I have
used to shift "logic-block" oscillators is to vary their supply voltage,
they will oscillate from around 3v to well over 5.5v that might enable
you to phase lock it  using a variable regulator to vcxo to crystal??

Alan G3NYK


- Original Message -
From: "Rex Moncur" 
To: "'Discussion of precise time and frequency measurement'"

Sent: Monday, June 01, 2009 10:59 PM
Subject: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references


>
> Hi all
>
> Does anyone have any experience of locking a USB external soundcard to a
> GPSDO 10 MHz reference.
>
> I am interested in advice on any good quality soundcards that can be
readily
> locked to either 10 MHz or if necessary to some other frequency that we
can
> derive from a GPSDO source.  I have done some tests with the SignalLink
> soundcard that uses a Texas Instruments PCM2904 chip and requires a 12 MHz
> lock frequency.  This requires some cutting of tracks to remove the
internal
> oscillator feedback and insert the locking frequency.  12 MHz is readily
> derived from 10 MHz but I have not been able to get it to lock.  The Texas
> instruments data sheet suggests that it is possible to use an external
> refernce but also says this is not recommended.  With this expereicne I
> would rather find a sound card that is designed for external locking that
> does not require the cutting of tracks.
>
> For info the purpose of this request is that we are looking at using very
> narrow bandwidth modes at less than 1 mHz for light wave communcation.  To
> date using LEDs and cloud reflection we have worked over 200 km with WSJT
> but we should be able to do 20 dB better if we can get down to milli-Hz
> bandwidths (at the expense of spending all night to complete a QSO). Our
> expereince to date is that standard sound cards are just not stable to
> better than 5 milli-Hz at 1000 Hz which should be readily solved by GPS
> locking let us get down to sub milli-Hz levels.
>
> Rex VK7MO
>
>
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Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-01 Thread Jeffrey Pawlan

Soundcards for USB are poor at best.

I have a set of PCI cards that were previously made by EMU and they accept 
external reference input.  They no longer make the model I have but perhaps 
they have another PCI card with an external ref input.


I am interested in your modulation technique which allows you to use WSJT.
Please let me know exactly what you are doing. I also do not know how you are 
using 5 milliHertz with WSJT since the group of discrete tones occupy more 
bandwidth.



73,

Jeffrey Pawlan  WA6KBL


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[time-nuts] Sound Cards for locking to GPSDO 10 MHz references

2009-06-01 Thread Rex Moncur
 
Hi all 

Does anyone have any experience of locking a USB external soundcard to a
GPSDO 10 MHz reference.

I am interested in advice on any good quality soundcards that can be readily
locked to either 10 MHz or if necessary to some other frequency that we can
derive from a GPSDO source.  I have done some tests with the SignalLink
soundcard that uses a Texas Instruments PCM2904 chip and requires a 12 MHz
lock frequency.  This requires some cutting of tracks to remove the internal
oscillator feedback and insert the locking frequency.  12 MHz is readily
derived from 10 MHz but I have not been able to get it to lock.  The Texas
instruments data sheet suggests that it is possible to use an external
refernce but also says this is not recommended.  With this expereicne I
would rather find a sound card that is designed for external locking that
does not require the cutting of tracks.

For info the purpose of this request is that we are looking at using very
narrow bandwidth modes at less than 1 mHz for light wave communcation.  To
date using LEDs and cloud reflection we have worked over 200 km with WSJT
but we should be able to do 20 dB better if we can get down to milli-Hz
bandwidths (at the expense of spending all night to complete a QSO). Our
expereince to date is that standard sound cards are just not stable to
better than 5 milli-Hz at 1000 Hz which should be readily solved by GPS
locking let us get down to sub milli-Hz levels.

Rex VK7MO


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