Re: [time-nuts] Data collection from 5115A phase noise test set?

[John Miles]

> It seems there is no way to estimate frequency from looking at the phase

> data then?

 

Not to my knowledge.  The frequency count chart on the instrument itself is 
always correct, since it can take the internal baseband offset out of the 
incoming data.  Because TimeLab doesn't have access to that offset, its 
frequency count chart won't be accurate when acquiring data from the 51xx.

 

> Does TimeLab have automated collection for the frequency-counter data on

> the control port?

 

TimeLab doesn't, but I have another collection of quick-and-dirty utilities 
that includes a way to do it (http://www.ke5fx.com/gpib/readme.htm).   The 
tsccmd.bat file can be run without any arguments to get command help; this 
option in particular will pull the frequency count entries across as ASCII text:

 



   C:\Program Files (x86)\KE5FX\GPIB>tsccmd 192.168.1.225 "show fcounter"

   Using Windows Sockets V2.2 (WinSock 2.0)

   Initializing host JMCORE64, address 192.168.1.200

   Attempting to connect to server 192.168.1.225:1299 . . .

   Connected to server 192.168.1.225:1299

   Transmitting "show fcounter" ...

   show fcounter

   Welcome to the Symmetricom 5125A

 

   =192.168.1.225 > Reference Frequency: 100.0 MHz (auto)

 

   Avg Time (s)Frequency (MHz)

   1   9.999627589

   10  9.9996274766

   100 9.99962746890

 

   Done, 8 line(s) received

   Average rate = 11.0/sec



 

 

There's probably a way (wget?) to do something similar in most other OSes -- 
you basically need to send "show fcounter" to port 1299 with an appropriate 
timeout interval.  Then you can pipe the response to something that parses the 
text that comes back, if desired.

 

-- john, KE5FX

Miles Design LLC

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Re: [time-nuts] Data collection from 5115A phase noise test set?

[Anders Wallin]

Thanks for these useful comments!

It seems there is no way to estimate frequency from looking at the phase
data then?
Does TimeLab have automated collection for the frequency-counter data on
the control port?

Anders


On Fri, Dec 11, 2015 at 2:51 AM, John Miles  wrote:

> > Hi all,
> >
> > A 5115A phase noise test set landed in our lab and I am wondering about
> the
> > data collection.
> > It has two telnet ports one for commands and one for phase data.
> > When issuing "start" on the command-port it starts spitting out
> > phase-difference values on the data port.
> >
> > However it seems to me that the phase data alone (REF-DUT phase, in units
> > of the REF period) is almost useless without knowing the internal
> workings
> > of the device.
> > The phase values are clearly not the true phase difference, which would
> > quickly accumulate to a huge number with e.g. REF=10MHz and DUT=11MHz.
> > My
> > understanding is that digital downconversion (DDC) is performed on both
> REF
> > and DUT signals, and without knowing the LO frequencies for the DDC the
> raw
> > phase data alone is almost useless.
> >
> > The command prompt does have commands for displaying the internally
> > calculated ADEV, L(f), frequency-counter readings, etc. and these seem to
> > show correct and OK values, but there seems to be no way to reproduce
> e.g.
> > the ADEV or frequency-counter values/statistics from the raw phase values
> > on the data port??
> > Is this correct? Any other experiences with the 5115A or higher end
> 5120A?
>
> The shorter-term ADEV values on the 5120A/5125A test sets are
> mathematically backed out of the phase noise data.  They will never
> perfectly match the ADEV values you get from plotting the phase data stream
> in my experience.
>
> I don't actually know what they do on the 5115A, though -- since it
> doesn't do cross-correlated PN, there's presumably no reason to derive the
> short-term ADEV plot from the PN data pipeline.  I'd expect the plots to
> match in that case, apart from any errors due to different measurement
> bandwidths and ADEV bin distributions.
>
> It's also true that there will always be an arbitrary phase slope error
> due to the mismatch between the frequency estimate used to tune the
> internal DDCs and the "real" frequency of the incoming data.  Knowledge of
> the actual DDC core frequencies would not be enough to correct for this
> behavior, because you would also need to know how far off they are.  The
> true frequency offset can't be measured ahead of time with perfect
> certainty, so it has to be estimated, and the resulting error will often
> dominate the slope of the phase-difference graph.
>
> The TimePod and 3120A test sets allow you to specify the input and
> reference frequencies explicitly to obtain a valid phase slope in residual
> measurements and other cases where the exact frequencies are known by the
> user.  But this is something you have to remember to do prior to the
> measurement, and you still don't get a calibrated absolute offset.
>
> (Also, note that TimeLab can read both phase and PN data from 51xx test
> sets without the need to use a Telnet client.  Not that it helps with this
> particular issue, of course.)
>
> -- john, KE5FX
> Miles Design LLC
>
>
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[time-nuts] Data collection from 5115A phase noise test set?

[Anders Wallin]

Hi all,

A 5115A phase noise test set landed in our lab and I am wondering about the
data collection.
It has two telnet ports one for commands and one for phase data.
When issuing "start" on the command-port it starts spitting out
phase-difference values on the data port.

However it seems to me that the phase data alone (REF-DUT phase, in units
of the REF period) is almost useless without knowing the internal workings
of the device.
The phase values are clearly not the true phase difference, which would
quickly accumulate to a huge number with e.g. REF=10MHz and DUT=11MHz. My
understanding is that digital downconversion (DDC) is performed on both REF
and DUT signals, and without knowing the LO frequencies for the DDC the raw
phase data alone is almost useless.

The command prompt does have commands for displaying the internally
calculated ADEV, L(f), frequency-counter readings, etc. and these seem to
show correct and OK values, but there seems to be no way to reproduce e.g.
the ADEV or frequency-counter values/statistics from the raw phase values
on the data port??
Is this correct? Any other experiences with the 5115A or higher end 5120A?

thanks,
Anders
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Re: [time-nuts] Data collection from 5115A phase noise test set?

[Tom Van Baak]

Lucky you! The 5115A has a thousand times better resolution than a hp5370 or 
SR620 counter.

The architecture of the 5110A 5115A and 5120A is described in the manuals. 
These are frequency stability analyzers so the initial phase and frequency 
offsets are not important. What you're seeing is phase difference data *after* 
these initial calibration offsets are removed. This is necessary because the 
unit allows a wide-range of frequencies on either port.

That method also keeps the floating point output from losing accuracy over long 
runs. A count of raw cycles would grow unbounded and you would lose resolution 
as you gained range. So what you're seeing is by design and it doesn't affect 
the phase noise or ADEV plots at all. I'm not sure why you call it "useless".

Note the 5110A has a single-DDS option. When both inputs are nominally the same 
frequency the streaming data is closer to raw phase. Not sure if the 5115/5120 
does also. But either way, none of this matters to ADEV.

Your ADEV plots from raw data should match the ADEV plots on the screen. Watch 
out for bandwidth mismatch.

/tvb


- Original Message - 
From: "Anders Wallin" <anders.e.e.wal...@gmail.com>
To: "Discussion" <time-nuts@febo.com>
Sent: Thursday, December 10, 2015 7:20 AM
Subject: [time-nuts] Data collection from 5115A phase noise test set?


> Hi all,
> 
> A 5115A phase noise test set landed in our lab and I am wondering about the
> data collection.
> It has two telnet ports one for commands and one for phase data.
> When issuing "start" on the command-port it starts spitting out
> phase-difference values on the data port.
> 
> However it seems to me that the phase data alone (REF-DUT phase, in units
> of the REF period) is almost useless without knowing the internal workings
> of the device.
> The phase values are clearly not the true phase difference, which would
> quickly accumulate to a huge number with e.g. REF=10MHz and DUT=11MHz. My
> understanding is that digital downconversion (DDC) is performed on both REF
> and DUT signals, and without knowing the LO frequencies for the DDC the raw
> phase data alone is almost useless.
> 
> The command prompt does have commands for displaying the internally
> calculated ADEV, L(f), frequency-counter readings, etc. and these seem to
> show correct and OK values, but there seems to be no way to reproduce e.g.
> the ADEV or frequency-counter values/statistics from the raw phase values
> on the data port??
> Is this correct? Any other experiences with the 5115A or higher end 5120A?
> 
> thanks,
> Anders

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Re: [time-nuts] Data collection from 5115A phase noise test set?

[John Ackermann N8UR]

There is a gotcha in the TSC phase data... the architecture introduces a 
deliberate phase offset to the phase data so you will always gain (or 
lose) phase over time.  Hook both inputs to the same source, and you'll 
still have a slope in the output data (and the slope and intercept will 
be different on each run).


Thus you *cannot* derive the actual frequency or phase offset from the 
phase data -- it is only useful for stability and phase noise analysis. 
 The TSC people told me this was a feature, not a bug. :-)  If you want 
to get the actual frequency of the DUT, you need to use the fcounter 
function.  And I've never been sure about the averaging used to derive 
the 1/10/100/1000 second values from fcounter, and how best to derive a 
longer-term frequency average from that data.


John

On 12/10/2015 1:44 PM, Tom Van Baak wrote:

Lucky you! The 5115A has a thousand times better resolution than a hp5370 or 
SR620 counter.

The architecture of the 5110A 5115A and 5120A is described in the manuals. 
These are frequency stability analyzers so the initial phase and frequency 
offsets are not important. What you're seeing is phase difference data *after* 
these initial calibration offsets are removed. This is necessary because the 
unit allows a wide-range of frequencies on either port.

That method also keeps the floating point output from losing accuracy over long runs. A 
count of raw cycles would grow unbounded and you would lose resolution as you gained 
range. So what you're seeing is by design and it doesn't affect the phase noise or ADEV 
plots at all. I'm not sure why you call it "useless".

Note the 5110A has a single-DDS option. When both inputs are nominally the same 
frequency the streaming data is closer to raw phase. Not sure if the 5115/5120 
does also. But either way, none of this matters to ADEV.

Your ADEV plots from raw data should match the ADEV plots on the screen. Watch 
out for bandwidth mismatch.

/tvb


- Original Message -
From: "Anders Wallin" <anders.e.e.wal...@gmail.com>
To: "Discussion" <time-nuts@febo.com>
Sent: Thursday, December 10, 2015 7:20 AM
Subject: [time-nuts] Data collection from 5115A phase noise test set?



Hi all,

A 5115A phase noise test set landed in our lab and I am wondering about the
data collection.
It has two telnet ports one for commands and one for phase data.
When issuing "start" on the command-port it starts spitting out
phase-difference values on the data port.

However it seems to me that the phase data alone (REF-DUT phase, in units
of the REF period) is almost useless without knowing the internal workings
of the device.
The phase values are clearly not the true phase difference, which would
quickly accumulate to a huge number with e.g. REF=10MHz and DUT=11MHz. My
understanding is that digital downconversion (DDC) is performed on both REF
and DUT signals, and without knowing the LO frequencies for the DDC the raw
phase data alone is almost useless.

The command prompt does have commands for displaying the internally
calculated ADEV, L(f), frequency-counter readings, etc. and these seem to
show correct and OK values, but there seems to be no way to reproduce e.g.
the ADEV or frequency-counter values/statistics from the raw phase values
on the data port??
Is this correct? Any other experiences with the 5115A or higher end 5120A?

thanks,
Anders


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Re: [time-nuts] Data collection from 5115A phase noise test set?

[John Miles]

> Hi all,
> 
> A 5115A phase noise test set landed in our lab and I am wondering about the
> data collection.
> It has two telnet ports one for commands and one for phase data.
> When issuing "start" on the command-port it starts spitting out
> phase-difference values on the data port.
> 
> However it seems to me that the phase data alone (REF-DUT phase, in units
> of the REF period) is almost useless without knowing the internal workings
> of the device.
> The phase values are clearly not the true phase difference, which would
> quickly accumulate to a huge number with e.g. REF=10MHz and DUT=11MHz.
> My
> understanding is that digital downconversion (DDC) is performed on both REF
> and DUT signals, and without knowing the LO frequencies for the DDC the raw
> phase data alone is almost useless.
> 
> The command prompt does have commands for displaying the internally
> calculated ADEV, L(f), frequency-counter readings, etc. and these seem to
> show correct and OK values, but there seems to be no way to reproduce e.g.
> the ADEV or frequency-counter values/statistics from the raw phase values
> on the data port??
> Is this correct? Any other experiences with the 5115A or higher end 5120A?

The shorter-term ADEV values on the 5120A/5125A test sets are mathematically 
backed out of the phase noise data.  They will never perfectly match the ADEV 
values you get from plotting the phase data stream in my experience.  

I don't actually know what they do on the 5115A, though -- since it doesn't do 
cross-correlated PN, there's presumably no reason to derive the short-term ADEV 
plot from the PN data pipeline.  I'd expect the plots to match in that case, 
apart from any errors due to different measurement bandwidths and ADEV bin 
distributions.

It's also true that there will always be an arbitrary phase slope error due to 
the mismatch between the frequency estimate used to tune the internal DDCs and 
the "real" frequency of the incoming data.  Knowledge of the actual DDC core 
frequencies would not be enough to correct for this behavior, because you would 
also need to know how far off they are.  The true frequency offset can't be 
measured ahead of time with perfect certainty, so it has to be estimated, and 
the resulting error will often dominate the slope of the phase-difference graph.

The TimePod and 3120A test sets allow you to specify the input and reference 
frequencies explicitly to obtain a valid phase slope in residual measurements 
and other cases where the exact frequencies are known by the user.  But this is 
something you have to remember to do prior to the measurement, and you still 
don't get a calibrated absolute offset. 

(Also, note that TimeLab can read both phase and PN data from 51xx test sets 
without the need to use a Telnet client.  Not that it helps with this 
particular issue, of course.)

-- john, KE5FX
Miles Design LLC


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