Re: [time-nuts] Close-in phase noise measurements

[Bernd T-Online]

Shane wrote:
> Do you know much about the R&S FSUP50?
> 
> http://www2.rohde-schwarz.com/en/products/test_and_measurement/product_categ
> ories/spectrum_analysis/FSUP-%7C-Key_Facts-%7C-4-%7C-966.html
> 

This is a nice but expensive equipment.
Nice: can do PN measurement by phase quadrature(where you need to 
oscillators) _and_ can doe cross-correlation measuremnts (where you need 
only one external oscillator).
Expensive: depending on options abt US-$ 100,000 to $150,000

If you are ready to spend so much money, consider the Agilent Signal 
Source Analyser 5052B, who does use the cross-correlation method and has 
a lot of other features.

But both of them are no ham gear yet...

Regards

Bernd Neubig
__
AXTAL GmbH & Co. KG
Facility MOS
Wasemweg 5
D-74821 Mosbach / Germany
fon: +49 (6261) 939834
fax: +49 (6261) 939836
www.axtal.com

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Re: [time-nuts] Close-in phase noise measurements

[Bruce Griffiths]

Shane wrote:
> Do you know much about the R&S FSUP50?
>
> http://www2.rohde-schwarz.com/en/products/test_and_measurement/product_categ
> ories/spectrum_analysis/FSUP-%7C-Key_Facts-%7C-4-%7C-966.html
>
>
>   
Shane

Only whats specified on the datasheet.

Its performance appears to be several 10's of dB worse than the state of 
the art (at low frequency offsets) when using the internal reference 
oscillator even when using cross correlation.
Not clear how much this is improved with an external reference oscillator.
It would be nice to know what the instrument noise floor (exclusive of 
its internal reference) is.

Bruce

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Re: [time-nuts] Close-in phase noise measurements

[Bruce Griffiths]

Bruce Griffiths wrote:
> John Miles wrote:
>   
>>> A dual mixer time difference system can have a lower noise floor than a
>>> single mixer system.
>>> 
>>>   
>> I wonder if those are still covered by patents in various corners of the
>> world, the way the TSC's dual-ADC architecture appears to be...
>>
>> -- john, KE5FX
>>
>>   
>> 
> John
>
> Unlikely, the dual mixer time difference technique has been around so 
> long that most patents like:
>
> United States Patent 5128909 (issued  7 July 1992, expired on 7 July 2004).
>
> which is an extension of the technique to multiple channels, have expired.
>
> Bruce
>
>   
Addenda

US patent 4,425,543 issued (JPL NASA) on Jan 10, 1984 has also passed 
its expiry date.
This covers the 1Hz beat frequency system developed at JPL.

Since NIST and others were using the technique well before 1984 its 
likely that any other relevant patents have long since expired.

However the new JPL system using a 123Hz beat frequency may have some 
associated patents, although its hard to see much justification for a 
patent.

Bruce

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Re: [time-nuts] Close-in phase noise measurements

[Bruce Griffiths]

John Miles wrote:
>> Most, but not all, sound cards have a low frequency cutoff of 20Hz or so.
>> Some (but not all) sound card ADCs can dc coupled.
>> A high resolution dc coupled ADC may be more effective for frequencies
>> below 20Hz.
>> 
>
> True; I'm assuming that anyone using a sound card for these purposes is
> either going to bypass the coupling capacitor in front of the ADC, or
> calibrate out the highpass response by adding an inverse function.  (A QEX
> article gave an example of the latter technique not too long ago.)
>
> I'm still hoping to get a 24-bit, 2.5-MSPS ADC chip hooked up via USB 2.0
> fairly soon.  That will solve a multitude of problems, eliminating the need
> for both a sound card and an HF analyzer.  I have C code on the PC that's
> talking to the FPGA, but haven't yet tried to bring the ADC up with it.
>
>   
>> Sound card support appears to be something of a minefield, baudline
>> thinks my 16 bit 48kHz motherboard sound system is a 24 bit 192kHz system.
>> This probably means that the frequency scale and consequently FFT filter
>> noise bandwidths are unreliable.
>> However with a low frequency noise calibration source and set of marker
>> harmonics derived from a crystal these calibration issues can be resolved.
>> Windows software fares little better and some crashes when set to sample
>> at 192kHz (the windows machine has a sound system with a 192kHz 20 bit
>> ADC system).
>> 
>
> Yeah, I think it'd be better not to even use the sound-card drivers if
> possible.  At 10 million bytes per second (32 bits/sample at 2.5 MSPS) they
> won't be an option for the hardware I'm looking at.
>
>   
That would be the AD7760 then?
>> A dual mixer time difference system can have a lower noise floor than a
>> single mixer system.
>> 
>
> I wonder if those are still covered by patents in various corners of the
> world, the way the TSC's dual-ADC architecture appears to be...
>
> -- john, KE5FX
>
>   
John

Unlikely, the dual mixer time difference technique has been around so 
long that most patents like:

United States Patent 5128909 (issued  7 July 1992, expired on 7 July 2004).

which is an extension of the technique to multiple channels, have expired.

Bruce

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Re: [time-nuts] Close-in phase noise measurements

[John Miles]

> Most, but not all, sound cards have a low frequency cutoff of 20Hz or so.
> Some (but not all) sound card ADCs can dc coupled.
> A high resolution dc coupled ADC may be more effective for frequencies
> below 20Hz.

True; I'm assuming that anyone using a sound card for these purposes is
either going to bypass the coupling capacitor in front of the ADC, or
calibrate out the highpass response by adding an inverse function.  (A QEX
article gave an example of the latter technique not too long ago.)

I'm still hoping to get a 24-bit, 2.5-MSPS ADC chip hooked up via USB 2.0
fairly soon.  That will solve a multitude of problems, eliminating the need
for both a sound card and an HF analyzer.  I have C code on the PC that's
talking to the FPGA, but haven't yet tried to bring the ADC up with it.

> Sound card support appears to be something of a minefield, baudline
> thinks my 16 bit 48kHz motherboard sound system is a 24 bit 192kHz system.
> This probably means that the frequency scale and consequently FFT filter
> noise bandwidths are unreliable.
> However with a low frequency noise calibration source and set of marker
> harmonics derived from a crystal these calibration issues can be resolved.
> Windows software fares little better and some crashes when set to sample
> at 192kHz (the windows machine has a sound system with a 192kHz 20 bit
> ADC system).

Yeah, I think it'd be better not to even use the sound-card drivers if
possible.  At 10 million bytes per second (32 bits/sample at 2.5 MSPS) they
won't be an option for the hardware I'm looking at.

> A dual mixer time difference system can have a lower noise floor than a
> single mixer system.

I wonder if those are still covered by patents in various corners of the
world, the way the TSC's dual-ADC architecture appears to be...

-- john, KE5FX


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Re: [time-nuts] Close-in phase noise measurements

[Shane]

Do you know much about the R&S FSUP50?

http://www2.rohde-schwarz.com/en/products/test_and_measurement/product_categ
ories/spectrum_analysis/FSUP-%7C-Key_Facts-%7C-4-%7C-966.html


-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Bruce Griffiths
Sent: Tuesday, March 25, 2008 8:22 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Close-in phase noise measurements

Shane wrote:
> Wenzel has a setup you can purchase at low cost.  
>
> http://www.wenzel.com/pdffiles1/PNTS%201000/BP-1000-SC.pdf
>
> Phase noise test sets can be pricey... $200K
>   
Shane

Their calibration method is somewhat problematic at the low frequency 
end where the effect of the PLL and the audio amplifier low frequency 
cutoff may be significant.
The NIST calibration technique: 
http://tf.nist.gov/timefreq/general/pdf/1000.pdf is far superior.

Bruce

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Re: [time-nuts] Close-in phase noise measurements

[Bruce Griffiths]

Shane wrote:
> Wenzel has a setup you can purchase at low cost.  
>
> http://www.wenzel.com/pdffiles1/PNTS%201000/BP-1000-SC.pdf
>
> Phase noise test sets can be pricey... $200K
>   
Shane

Their calibration method is somewhat problematic at the low frequency 
end where the effect of the PLL and the audio amplifier low frequency 
cutoff may be significant.
The NIST calibration technique: 
http://tf.nist.gov/timefreq/general/pdf/1000.pdf is far superior.

Bruce

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Re: [time-nuts] Close-in phase noise measurements

[Shane]

Wenzel has a setup you can purchase at low cost.  

http://www.wenzel.com/pdffiles1/PNTS%201000/BP-1000-SC.pdf

Phase noise test sets can be pricey... $200K

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Bruce Griffiths
Sent: Tuesday, March 25, 2008 5:43 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Close-in phase noise measurements

John Miles wrote:
>> I am continuing my phase noise measurement quest. I gathered
>> equipment (HP 8662a/11729C/8568B/multipliers) to measure
>> 100Hz+ from the carrier. I now need to get a grip on the
>> 0.1-100Hz range, which is where most of my applications are.
>>
>> What is the suggested measurement methodology for this range?
>>
>> My first idea would be to squeeze out the most of the above
>> equipment...maybe add a dynamic signal analyzer like the
>> 35660/3561/3562? What is a good HP LF analyzer?
>> This combined with multiplication (to 1GHz) and EFC
>> locking, could take care of the 1-100HZ range?
>> Anythings else needed?
>> No ideas for  0.1-1... maybe by counting with the 5370B?
>>
>> I am sure this has been answered before but the archives are
>> difficult to search...
>> 
>
> So, I've started to look into the sub-100 Hz regime lately, but haven't
had
> time to get very serious about it.  Here's my take on the question:
>
> 1) The TSC-51xx analyzers are sure nifty if you have the budget and can
live
> with being limited to HF measurements.  They offer high performance with
> less fiddling around than any other PN-measurement platform I've seen.
>
>   
The range can be extended with a couple of external mixers (plus low 
pass IF filters) and a low noise offset source.
The offset source is mixed with each of the signals to be compared to 
produce a pair of IF frequencies within the 0-30MHz range.
> 2) The next best thing would be a sound-card FFT option that works in
> conjunction with an HF analyzer.  PN.EXE will do this at some point, using
> the 11729's front-panel LF analyzer output.  It's really just a matter of
> writing the UI code to support it.
>
>   
Most, but not all, sound cards have a low frequency cutoff of 20Hz or so.
Some (but not all) sound card ADCs can dc coupled.
A high resolution dc coupled ADC may be more effective for frequencies 
below 20Hz.
> 3) The next best thing, after that, is a dedicated FFT analyzer, perhaps
in
> conjunction with an HP 3047A or 3048A system (i.e., an FFT analyzer plus a
> 35601A or 11848A interface).  Boxes like the HP 3561A and 3562A are neat,
> but they are complete technological relics.  They are limited to about 80
dB
> of dynamic range in a 100-kHz bandwidth, they take up quite a bit of
space,
> and they require either a lot of custom coding or some obsolete HP
software.
> The 3582A is in the same boat, only more so.  An 11729B/C plus a simple
> sound-card interface will be the clear winner once the software support
> issue is resolved.
>
>   
Sound card support appears to be something of a minefield, baudline 
thinks my 16 bit 48kHz motherboard sound system is a 24 bit 192kHz system.
This probably means that the frequency scale and consequently FFT filter 
noise bandwidths are unreliable.
However with a low frequency noise calibration source and set of marker 
harmonics derived from a crystal these calibration issues can be resolved.
Windows software fares little better and some crashes when set to sample 
at 192kHz (the windows machine has a sound system with a 192kHz 20 bit 
ADC system).
> Disclaimer: I do have a 3561A and a 3562A.  They are really cool boxes,
but
> if I ever write any code to support them in PN.EXE, it'll be because I
think
> they're cool, not because I think they're the right answer for any
> FFT-analysis applications today.  Technology has left them behind in a
> drastic way that hasn't happened with RF spectrum analyzers.
>
> An FFT analyzer can still be used at offsets below 1 Hz, but at that point
> people usually want to see Allan-deviation graphs rather than PN graphs.
It
> becomes a different problem, since you most likely want to use a counter
> rather than a spectrum analyzer.
>
> -- john, KE5FX
>   
A finite beat frequency is required when using a counter.
With low beat frequencies a lower noise zero crossing detector than the 
counter input trigger circuitry is required to minimise system noise.

A dual mixer time difference system can have a lower noise floor than a 
single mixer system.

Bruce

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Re: [time-nuts] GPS and national standards in frequency

[Bruce Griffiths]

Marco A. Ferra wrote:
> Thanks Mike, I'll give it a close look.
>
> Sincere regards,
> Marco 
>
> -Original Message-
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Mike S
> Sent: terça-feira, 25 de Março de 2008 1:53
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] GPS and national standards in frequency
>
> You might want to read this: http://tf.nist.gov/service/gpscal.htm
>
> At 09:27 PM 3/24/2008, Marco A. Ferra wrote...
>   
>> Dear time-nuts
>>
>> My name is Marco Ferra.  I'm doing research on an electrical metrology 
>> laboratory in Portugal, and I'm conducting a study on how to establish 
>> tracebility to frequency using one (or more) GPSDO's.  I came across 
>> febo.com's site and this mailing list after searching the net.  Let me 
>> tell you what I'm doing.
>>
>> I have put side-by-side two GPS receivers, one HP58503 (now owned by 
>> Symmetricom I believe) and a Fluke 910R, both with it's own antenna.
>> Both antennas are separated by about 100 meters.  I'm tracking the 10 
>> MHz output of both GPS receivers with a Fluke PM6681R Counter.  I'm 
>> using the internal Rubidium oscillator of the counter and using 
>> channels A and B for the measurements.  Each 10 seconds, I'm recording 
>> the frequency on channel A, B, and the phase (in degrees) between the 
>> two signals.  I have resolution on the phase by 1/10th of degree.
>>
>> With the phase, I can get the time differente in nano-seconds between 
>> the two signals:
>>
>> =phase(degress)/(360*1000)*10^9
>>
>> I'm putting 1000 Hz has a nominal frequency for the calculation, 
>> I'm not sure if should use the frequency recorded on channel A or B.
>>
>> Then I calculate the time difference, the TIE (ns), the Delta Tie (ns) 
>> accumulative, and then the Delta f (it's equal to Delta TIE (ACC) / 
>> measurement time (could be 10, 20, 30 secs)).  Please take a grasp at 
>> page 4 of 
>> http://www.pendulum-instruments.com/Assets/download/accurate_calibratio
>> n
>> _article.pdf
>>
>> Given these two GPSDO's, and given the very small Delta f, I can assume 
>> that both GPSDO's are functioning proprely (could I indeed?).  But I'm 
>> not sure how I can get tracebility to national standards, to NIST, for 
>> example, on the 10 MHz output frequency.  Perhaps it's difficult, but I 
>> need a solid proof that my 10 MHz output is traceble to a primary 
>> laboratory.
>>
>> I have seen that you all have a vast experience in this area, and 
>> perhaps we could work together to gather good results and achive this 
>> goal.
>>
>> Sincere regards, and thank you for reading, Marco
>>
>> 
You will do much better if you divide the frequencies to be calibrated 
down to 1Hz and time stamp the 1Hz signal transitions and the leading 
edge of the leading edge of the PPS output of a modern GPS timing 
receiver. Record the timestamps along with the associated GPS receiver 
sawtooth corrections. This is what NIST does in their remote frequency 
measurement systems. The recorded data is analysed along with NISTs  own 
measurements using a similar setup driven by one of their caesium 
clocks. A time stamp resolution better than 1ns is necessary to avoid 
significantly degrading the performance achievable with a modern timing 
receiver.

Using an indirect method such as employing a GPSDO (particularly one 
using a legacy timing receiver) just adds another layer of uncertainty 
to the traceability chain.

Even better resolution is possible by making GPS carrier phase 
measurements, however this requires that the GPS receiver local 
oscillators etc, be locked to the frequency source being characterised.

Since neither NIST nor your local NMI control the GPS system 
traceability using GPS requires that both you and your NMI make such 
measurements.
If you are not too far away from your NMI then both you and your NMI 
will experience essentially the same GPS timing fluctuations due to 
common mode effects such as GPS SV transmission fluctuations and 
ionospheric delays.

Bruce

Bruce

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Re: [time-nuts] new GPSDO available

[SAIDJACK]

Hello Joe,
 
thanks for the feedback and questions! Some other members asked for more  
details, I will send out more technical details in the next day or two.
 
You can make an SNTP time server with the FireFly or Fury GPSDO in two  ways:
 
1) The simple way of doing it:
 
Connect a PC running GPSCon to either one of the two units via the serial  
port. GPSCon is quite inexpensive and works pretty well. It has a built-in SNTP 
 
server function among other features. I believe you can get it for less than 
$50  at realhamradio dot com. All you need is a Null Modem Cable, and  PC with 
 the software installed.
 
2) This way provides tighter timing accuracy, but requires soldering a  
single wire:
 
For better accuracy, you can run SNTP or NTP server software on a  Linux PC, 
and connect a 1PPS RS-232 level compatible signal to pin 4 of the Fury  or 
FireFly DB-9 connector. The PC will trigger on this signal (usually connected  
to 
DCD on the PC side) and provide a high accuracy time server. You can search  
the Time Nuts archives on how to set up Linux to do this.
 
The Fury and FireFly both support this 1PPS RS-232 level signal on the PCB,  
but it's not connected to the RS-232 connector by default. The user has to 
wire  it up to the DB-9 connector.
 
Let me know if anyone wants details on how to wire up their RS-232  connector 
for this.
 
Hope that helps,
 
bye,
Said
 
 
In a message dated 3/25/2008 14:53:28 Pacific Daylight Time,  
[EMAIL PROTECTED] writes:

Looks  very cool!  So how do I make, or have my Network Administrator make,  a
NTP time server from one of these or one of your other products?  I  am
technically inept and am in the market for a time server, Meinberg's  are
nice but out of my budget.  Any help is  appreciated.

Joe

-Original Message-
From:  [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of  [EMAIL PROTECTED]
Sent: Tuesday, March 25, 2008 1:15 PM
To:  time-nuts@febo.com
Subject: [time-nuts] new GPSDO available

Hi  guys,

sorry for the more or less commercial nature of this  email.

Wanted to share with you that we have shrunk our Fury GPSDO into  a 1 inch x

2.5 inch x 0.5 inch tiny little package, called the FireFly.  It's the most  
inexpensive new GPSDO that we know of at this  time.

It's less than 1/2 the size of a credit card.

The unit has  a subset of the Fury SCPI commands, generally it has the same   
features as the Fury. The performance is pretty good too, and  power
consumption 
was reduced to < 1.4W at 12V using a  high-stability small OCXO.

We are using a highly sensitive mobile GPS  receiver now, so it can be used  
in a moving car etc. The GPS  receiver is sensitive down to -151dBm
tracking. 
Some preliminary specs  are available at _www.jackson-labs.com_ 
(http://www.jackson-labs.com)  

We are sampling the units now. Let me know if anyone is interested in  more  
details, we are presently fully qualifying the  unit.

Bye,
Said



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Home.   
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00301)
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Re: [time-nuts] GPS and national standards in frequency

[Marco A. Ferra]

Thanks Mike, I'll give it a close look.

Sincere regards,
Marco 

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Mike S
Sent: terça-feira, 25 de Março de 2008 1:53
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] GPS and national standards in frequency

You might want to read this: http://tf.nist.gov/service/gpscal.htm

At 09:27 PM 3/24/2008, Marco A. Ferra wrote...
>Dear time-nuts
>
>My name is Marco Ferra.  I'm doing research on an electrical metrology 
>laboratory in Portugal, and I'm conducting a study on how to establish 
>tracebility to frequency using one (or more) GPSDO's.  I came across 
>febo.com's site and this mailing list after searching the net.  Let me 
>tell you what I'm doing.
>
>I have put side-by-side two GPS receivers, one HP58503 (now owned by 
>Symmetricom I believe) and a Fluke 910R, both with it's own antenna.
>Both antennas are separated by about 100 meters.  I'm tracking the 10 
>MHz output of both GPS receivers with a Fluke PM6681R Counter.  I'm 
>using the internal Rubidium oscillator of the counter and using 
>channels A and B for the measurements.  Each 10 seconds, I'm recording 
>the frequency on channel A, B, and the phase (in degrees) between the 
>two signals.  I have resolution on the phase by 1/10th of degree.
>
>With the phase, I can get the time differente in nano-seconds between 
>the two signals:
>
>=phase(degress)/(360*1000)*10^9
>
>I'm putting 1000 Hz has a nominal frequency for the calculation, 
>I'm not sure if should use the frequency recorded on channel A or B.
>
>Then I calculate the time difference, the TIE (ns), the Delta Tie (ns) 
>accumulative, and then the Delta f (it's equal to Delta TIE (ACC) / 
>measurement time (could be 10, 20, 30 secs)).  Please take a grasp at 
>page 4 of 
>http://www.pendulum-instruments.com/Assets/download/accurate_calibratio
>n
>_article.pdf
>
>Given these two GPSDO's, and given the very small Delta f, I can assume 
>that both GPSDO's are functioning proprely (could I indeed?).  But I'm 
>not sure how I can get tracebility to national standards, to NIST, for 
>example, on the 10 MHz output frequency.  Perhaps it's difficult, but I 
>need a solid proof that my 10 MHz output is traceble to a primary 
>laboratory.
>
>I have seen that you all have a vast experience in this area, and 
>perhaps we could work together to gather good results and achive this 
>goal.
>
>Sincere regards, and thank you for reading, Marco
>
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Re: [time-nuts] Close-in phase noise measurements

[Bruce Griffiths]

John Miles wrote:
>> I am continuing my phase noise measurement quest. I gathered
>> equipment (HP 8662a/11729C/8568B/multipliers) to measure
>> 100Hz+ from the carrier. I now need to get a grip on the
>> 0.1-100Hz range, which is where most of my applications are.
>>
>> What is the suggested measurement methodology for this range?
>>
>> My first idea would be to squeeze out the most of the above
>> equipment...maybe add a dynamic signal analyzer like the
>> 35660/3561/3562? What is a good HP LF analyzer?
>> This combined with multiplication (to 1GHz) and EFC
>> locking, could take care of the 1-100HZ range?
>> Anythings else needed?
>> No ideas for  0.1-1... maybe by counting with the 5370B?
>>
>> I am sure this has been answered before but the archives are
>> difficult to search...
>> 
>
> So, I've started to look into the sub-100 Hz regime lately, but haven't had
> time to get very serious about it.  Here's my take on the question:
>
> 1) The TSC-51xx analyzers are sure nifty if you have the budget and can live
> with being limited to HF measurements.  They offer high performance with
> less fiddling around than any other PN-measurement platform I've seen.
>
>   
The range can be extended with a couple of external mixers (plus low 
pass IF filters) and a low noise offset source.
The offset source is mixed with each of the signals to be compared to 
produce a pair of IF frequencies within the 0-30MHz range.
> 2) The next best thing would be a sound-card FFT option that works in
> conjunction with an HF analyzer.  PN.EXE will do this at some point, using
> the 11729's front-panel LF analyzer output.  It's really just a matter of
> writing the UI code to support it.
>
>   
Most, but not all, sound cards have a low frequency cutoff of 20Hz or so.
Some (but not all) sound card ADCs can dc coupled.
A high resolution dc coupled ADC may be more effective for frequencies 
below 20Hz.
> 3) The next best thing, after that, is a dedicated FFT analyzer, perhaps in
> conjunction with an HP 3047A or 3048A system (i.e., an FFT analyzer plus a
> 35601A or 11848A interface).  Boxes like the HP 3561A and 3562A are neat,
> but they are complete technological relics.  They are limited to about 80 dB
> of dynamic range in a 100-kHz bandwidth, they take up quite a bit of space,
> and they require either a lot of custom coding or some obsolete HP software.
> The 3582A is in the same boat, only more so.  An 11729B/C plus a simple
> sound-card interface will be the clear winner once the software support
> issue is resolved.
>
>   
Sound card support appears to be something of a minefield, baudline 
thinks my 16 bit 48kHz motherboard sound system is a 24 bit 192kHz system.
This probably means that the frequency scale and consequently FFT filter 
noise bandwidths are unreliable.
However with a low frequency noise calibration source and set of marker 
harmonics derived from a crystal these calibration issues can be resolved.
Windows software fares little better and some crashes when set to sample 
at 192kHz (the windows machine has a sound system with a 192kHz 20 bit 
ADC system).
> Disclaimer: I do have a 3561A and a 3562A.  They are really cool boxes, but
> if I ever write any code to support them in PN.EXE, it'll be because I think
> they're cool, not because I think they're the right answer for any
> FFT-analysis applications today.  Technology has left them behind in a
> drastic way that hasn't happened with RF spectrum analyzers.
>
> An FFT analyzer can still be used at offsets below 1 Hz, but at that point
> people usually want to see Allan-deviation graphs rather than PN graphs.  It
> becomes a different problem, since you most likely want to use a counter
> rather than a spectrum analyzer.
>
> -- john, KE5FX
>   
A finite beat frequency is required when using a counter.
With low beat frequencies a lower noise zero crossing detector than the 
counter input trigger circuitry is required to minimise system noise.

A dual mixer time difference system can have a lower noise floor than a 
single mixer system.

Bruce

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[time-nuts] Lessons learned, Odetics 3/425

[Bruce Lane]

Fellow clock-confusers,

I learned an important lesson today, while troubleshooting the GPS
receiver module in my Odetics clock for the 5th time. That lesson is
"Never assume that you've fixed an intermittent problem the first time."

The second part of the lesson is "Never assume the most complicated
failures. It's the simple stuff that'll get you in the end."

And, in this case, it was indeed very simple. The center pin of the
SMB-type antenna connector, on the GPS receiver board itself, had a
hairline fracture. I didn't discover this until I disassembled the thing
to work on it today, and found that the center pin was not only bent but
rotating freely around its center axis when I tried to straighten it.

I have ordered the necessary connectors from Allied to allow me to
completely re-do the antenna cable from front to back, including
replacing the push-on SMB crap with proper (and far more durable) SMA
parts.

This certainly explains why the thing has been intermittent since Day 1,
even though the pin seemed OK the last time I had it apart. What I can't
figure out is, given that the PCB outline on the receiver board is
clearly spaced for an SMA connection, why was an SMB put on there? Cost,
perhaps? Seems to me the SMB would actually be more expensive due to the
tolerances involved.

Happy timing.




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Re: [time-nuts] Close-in phase noise measurements

[John Miles]

> I am continuing my phase noise measurement quest. I gathered
> equipment (HP 8662a/11729C/8568B/multipliers) to measure
> 100Hz+ from the carrier. I now need to get a grip on the
> 0.1-100Hz range, which is where most of my applications are.
>
> What is the suggested measurement methodology for this range?
>
> My first idea would be to squeeze out the most of the above
> equipment...maybe add a dynamic signal analyzer like the
> 35660/3561/3562? What is a good HP LF analyzer?
> This combined with multiplication (to 1GHz) and EFC
> locking, could take care of the 1-100HZ range?
> Anythings else needed?
> No ideas for  0.1-1... maybe by counting with the 5370B?
>
> I am sure this has been answered before but the archives are
> difficult to search...

So, I've started to look into the sub-100 Hz regime lately, but haven't had
time to get very serious about it.  Here's my take on the question:

1) The TSC-51xx analyzers are sure nifty if you have the budget and can live
with being limited to HF measurements.  They offer high performance with
less fiddling around than any other PN-measurement platform I've seen.

2) The next best thing would be a sound-card FFT option that works in
conjunction with an HF analyzer.  PN.EXE will do this at some point, using
the 11729's front-panel LF analyzer output.  It's really just a matter of
writing the UI code to support it.

3) The next best thing, after that, is a dedicated FFT analyzer, perhaps in
conjunction with an HP 3047A or 3048A system (i.e., an FFT analyzer plus a
35601A or 11848A interface).  Boxes like the HP 3561A and 3562A are neat,
but they are complete technological relics.  They are limited to about 80 dB
of dynamic range in a 100-kHz bandwidth, they take up quite a bit of space,
and they require either a lot of custom coding or some obsolete HP software.
The 3582A is in the same boat, only more so.  An 11729B/C plus a simple
sound-card interface will be the clear winner once the software support
issue is resolved.

Disclaimer: I do have a 3561A and a 3562A.  They are really cool boxes, but
if I ever write any code to support them in PN.EXE, it'll be because I think
they're cool, not because I think they're the right answer for any
FFT-analysis applications today.  Technology has left them behind in a
drastic way that hasn't happened with RF spectrum analyzers.

An FFT analyzer can still be used at offsets below 1 Hz, but at that point
people usually want to see Allan-deviation graphs rather than PN graphs.  It
becomes a different problem, since you most likely want to use a counter
rather than a spectrum analyzer.

-- john, KE5FX


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[time-nuts] new GPSDO available

[SAIDJACK]

Hi guys,
 
sorry for the more or less commercial nature of this email.
 
Wanted to share with you that we have shrunk our Fury GPSDO into a 1 inch x  
2.5 inch x 0.5 inch tiny little package, called the FireFly. It's the most  
inexpensive new GPSDO that we know of at this time.
 
It's less than 1/2 the size of a credit card.
 
The unit has a subset of the Fury SCPI commands, generally it has the same  
features as the Fury. The performance is pretty good too, and power consumption 
 was reduced to < 1.4W at 12V using a high-stability small OCXO.
 
We are using a highly sensitive mobile GPS receiver now, so it can be used  
in a moving car etc. The GPS receiver is sensitive down to -151dBm  tracking. 
Some preliminary specs are available at _www.jackson-labs.com_ 
(http://www.jackson-labs.com) 
 
We are sampling the units now. Let me know if anyone is interested in more  
details, we are presently fully qualifying the unit.
 
Bye,
Said



**Create a Home Theater Like the Pros. Watch the video on AOL 
Home.  
(http://home.aol.com/diy/home-improvement-eric-stromer?video=15?ncid=aolhom000301)
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[time-nuts] Close-in phase noise measurements

[Christophe Huygens]

Hi,

I am continuing my phase noise measurement quest. I gathered
equipment (HP 8662a/11729C/8568B/multipliers) to measure
100Hz+ from the carrier. I now need to get a grip on the
0.1-100Hz range, which is where most of my applications are.

What is the suggested measurement methodology for this range?

My first idea would be to squeeze out the most of the above
equipment...maybe add a dynamic signal analyzer like the
35660/3561/3562? What is a good HP LF analyzer?
This combined with multiplication (to 1GHz) and EFC
locking, could take care of the 1-100HZ range?
Anythings else needed?
No ideas for  0.1-1... maybe by counting with the 5370B?

I am sure this has been answered before but the archives are
difficult to search...

Thanks for any hints,
Christophe
begin:vcard
fn:Christophe Huygens
n:Huygens;Christophe
org:K.U.Leuven;Dept. Computerwetenschappen
adr;dom:;;Celestijnenlaan 200A;Heverlee;;3001
email;internet:[EMAIL PROTECTED]
title:Gastdocent - Assistant Professor
tel;work:+3216327561
x-mozilla-html:FALSE
url:www.cs.kuleuven.ac.be/~xtof
version:2.1
end:vcard

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Re: [time-nuts] How best to compute local time from GPS

[Mike S]

At 11:07 PM 3/24/2008, David Forbes wrote...
>2. If I have to store the time zone from the user's input, are the
>DST calculations reasonably straightforward these days?
>
>3. What weird time zone operations should it support, such as 15
>minute local offsets or oddball DST dates?
>
>4. In general, is it better to let the user turn DST on and off or
>try to do it automatically? (I live in Arizona, which doesn't worship
>DST, so I have no experience in this matter.)

There is a well accepted method of specifying time zone offset and 
summer time adjustments. It is much simpler than trying to parse an 
Olson timezone table (which has historical information to allow date 
and calculations, something not needed for a clock). It allows for the 
full range of rules, and you don't have to worry about updating a table 
should the rules change. This is called a IEEE 1003.1 POSIX timezone 
literal. A good description is contained in 
http://tools.ietf.org/html/draft-ietf-dhc-dhcpv6-opt-tz-00

To specify the timezone for the eastern US, including current daylight 
saving time rules, one would use 
TZ="EST5EDT4,M3.2.0/02:00:00,M11.1.0/02:00:00"


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Re: [time-nuts] How best to compute local time from GPS

[Bruce Griffiths]

Magnus Danielson wrote:
>> Quoth David Forbes at 2008-03-25 13:37...
>> ...
>> 
>>> 2. If I have to store the time zone from the user's input, are the 
>>> DST calculations reasonably straightforward these days?
>>>
>>> 3. What weird time zone operations should it support, such as 15 
>>> minute local offsets or oddball DST dates?
>>>   
>> The problem with coding this stuff into your software is that it will be 
>> out of date no sooner have you hit 'compile'.  Whilst it would be cool 
>> to use the Zoneinfo database , 
>> it's quite big (about half a Meg, IIRC) and would also require network 
>> access.
>>
>> I'd be inclined to convert GPS time to UTC and then let the user set 
>> through the menu system their UCT offset in hours and minutes (I live in 
>> one of the daft half-hour timezones) and also DST start/end dates.  This 
>> gives you complete flexibility - which is required when the authorities 
>> keep messing around with their daylight-saving plans.
>> 
>
> I had the same thought, but with a twist. But first the general comment.
> You would have a hell to figure out what country and part of country you are 
> in
> from GPS position since that would require you a digitized zone-map and then a
> region-to-offset and DST table. As for DST, they change... US just changed for
> instance. Europe coordinated back in 2001 to common DST times. DST dates you
> must assume to be different wherever you go an the US have proved them to be a
> variable even today. 
Political boundaries can also change.
For example the Ethiopia/Eritrea border location hasnt yet been settled, 
although a proposal has been formulated for adoption.
NZ also changed the date for reverting from summertime, starting this year.
> As for offsets, to be fullblown generic, you need 15 min
> offsets. Actually, you would even require to support UT1 and UTC if you would
> support things correctly. Then we have those nations running solar time
> directly and then we have solar time, i.e. time of day from sun rise.
>
>   
Supporting UT1 to an accuracy of much better than 1sec is a little 
problematic unless one decodes the appropriate CNAV packet broadcast on L2C.
Unfortunately this isnt possible when using a legacy L1 only GPS receiver.
Alternatively one can download UT1-UTC predictions and adjust the stored 
offset as and when required.
At the moment UTC is kept within 0.9sec of UT1 by the leapsecond mechanism.
If and when leapseconds are done away with calculating UT1 to the same 
accuracy becomes problematic without the UT1-UTC correction broadcast on 
L2C or IERTS UT1-UTC predictions..
> It's a mess. Recent events is making it a bigger mess. Choose to support UTC
> plus an UTC offset and another UTC offset between certain dates. Now for the
> twist. Let a little computer software on the side aid in setting this thing 
> up.
> You can evolve that from a direct question application to one that does more
> and more complex analysis... when you feel like it, and without creating a
> heavier code in the scopeclock. 
>
>   
>> Anyone who hasn't seen David's scope clock stuff, it's seriously cool.
>> 
>
> I have an AVRclock, how do they compare?
>
> Cheers,
> Magnus
>   
Bruce

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Re: [time-nuts] How best to compute local time from GPS

[Magnus Danielson]

From: Matthew Smith <[EMAIL PROTECTED]>
Subject: Re: [time-nuts] How best to compute local time from GPS
Date: Tue, 25 Mar 2008 14:11:36 +1030
Message-ID: <[EMAIL PROTECTED]>

> Quoth David Forbes at 2008-03-25 13:37...
> ...
> > 2. If I have to store the time zone from the user's input, are the 
> > DST calculations reasonably straightforward these days?
> > 
> > 3. What weird time zone operations should it support, such as 15 
> > minute local offsets or oddball DST dates?
> 
> The problem with coding this stuff into your software is that it will be 
> out of date no sooner have you hit 'compile'.  Whilst it would be cool 
> to use the Zoneinfo database , 
> it's quite big (about half a Meg, IIRC) and would also require network 
> access.
> 
> I'd be inclined to convert GPS time to UTC and then let the user set 
> through the menu system their UCT offset in hours and minutes (I live in 
> one of the daft half-hour timezones) and also DST start/end dates.  This 
> gives you complete flexibility - which is required when the authorities 
> keep messing around with their daylight-saving plans.

I had the same thought, but with a twist. But first the general comment.
You would have a hell to figure out what country and part of country you are in
from GPS position since that would require you a digitized zone-map and then a
region-to-offset and DST table. As for DST, they change... US just changed for
instance. Europe coordinated back in 2001 to common DST times. DST dates you
must assume to be different wherever you go an the US have proved them to be a
variable even today. As for offsets, to be fullblown generic, you need 15 min
offsets. Actually, you would even require to support UT1 and UTC if you would
support things correctly. Then we have those nations running solar time
directly and then we have solar time, i.e. time of day from sun rise.

It's a mess. Recent events is making it a bigger mess. Choose to support UTC
plus an UTC offset and another UTC offset between certain dates. Now for the
twist. Let a little computer software on the side aid in setting this thing up.
You can evolve that from a direct question application to one that does more
and more complex analysis... when you feel like it, and without creating a
heavier code in the scopeclock. 

> Anyone who hasn't seen David's scope clock stuff, it's seriously cool.

I have an AVRclock, how do they compare?

Cheers,
Magnus

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Re: [time-nuts] How best to compute local time from GPS

[Morris Odell]

David Forbes asked:

>> 2. If I have to store the time zone from the user's input, are the
>> DST calculations reasonably straightforward these days?

It's not too difficult and you get a nice refresher in modulo-7 arithmetic. 
I did it in AVR assembler recently although I didn't try to make it 
universal. Our government down here in south-eastern Australia recently 
changed the DST changeover dates so I customised it for where I live. If you 
need to make it user settable that would mean you need to be able to enter 
the dates and UTC offsets as a menu item which would complicate things 
considerably. It'd be a fun programming challenge though :-)

>> 4. In general, is it better to let the user turn DST on and off or
>> try to do it automatically? (I live in Arizona, which doesn't worship
>> DST, so I have no experience in this matter.)

I put a 3 position (centre off) switch on the back panel of my clock. The 3 
positions are: Summer time, Auto, Winter time. That way after I'm demented 
or dead and gone if the gov't changes the rules again it can be changed 
manually.

I programmed the receiver for our local time offset from UTC. I then add or 
don't add an hour as the case may be.

Morris 


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