Re: [time-nuts] ADCs for phase noise measurement

[Bob Camp]

Hi

I think you will find that you need the DC890 add on board to run Pscope.

Bob


> On Jun 11, 2016, at 4:08 PM, Richard (Rick) Karlquist  
> wrote:
> 
> 
> 
> On 6/11/2016 6:33 AM, Attila Kinali wrote:
>> Hoi Rick,
>> 
>> use a small uC board to interface with the PC. Saving the samples in
>> a wav file and using one of the many FFT tools shouldn't be a problem.
>> 
> 
> This gets even better.  The free Pscope software comes with
> FFT.  I don't even need to fool with exporting a .file to
> some FFT program.
> 
> Rick
> 
> 
>> 
>>  Attila Kinali
>> 
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Re: [time-nuts] ADCs for phase noise measurement

[Attila Kinali]

On Sat, 11 Jun 2016 11:53:22 -0700
"Richard (Rick) Karlquist"  wrote:

> Good call on the LTC2368-24.  The eval board for it has considerably
> better support (like p-scope) than do the Analog Devices eval boards.
> I think this might work for me.  What are the tradeoffs between SAR
> and sigma-delta ADC?  

Good question, I don't really know. And it's a moving target too.

Currently it seems that sigma-delta ADCs reach higher SNR levels
and have less inherent noise. I am not sure whether they are better
at DNL but slighly worse at INL, but from the datasheets I had a look
at it seems so. The advantage of SAR is that they can reach quite
high sampling rates, going up to 15Msps for an 18bit ADC (LTC2387-18).
Though there are sigma-delta that are quite fast, like the AD7760
that can deliver up to 2.5Msps (but only at an SNR of 100dBFS).
Sigma-delta ADCs get worse performance when run faster (they havily
depend on averaging, filtering and noise shaping), while SAR have their
performance almost independent of sampling rate (but the non-linearities
of the internal components get more pronounced with higher sampling rate).
One thing is for sure though: sigma-delta ADCs get you more bits/SNR per buck,
as the high resolution SAR are still quite expensive. SAR ADCs seem to get
better by the day, so it is a good idea to check again what kind of
performance level they reached, once in a while. Sigma-delta do not
develop that fast anymore, but still see some increase in SNR and
sampling rate.


Which one is actually better is not so clear, as a sigma-delta converter
doesn't get to full resulution until you go wy down with the sampling
rate (or average). And because the target applications for the two types
of ADCs are slightly different, the datasheets are written differently,
so it's not easy to actually compare their performance. Even more so as
you will be decimating/filtering the samples quite heavily.

I guess for your application, the easiest way is to just buy some
eval boards that seem good and measure their performance directly.

> Can you point me to a few of the "many" FFT
> tools?  Maybe I don't have to buy spectrum analyzer software.


Hmm.. I couldn't find any of the tools I used (back 15 years ago).
But if nothing else works, you can use python (scipy+matplotlib)
or matlab/octave to read the data (all can read wav files)
and plot an fft (shouldn't be more than a couple of lines in any of
those languages). If you get stuck with that, let me know.


Attila Kinali

-- 
Malek's Law:
Any simple idea will be worded in the most complicated way.
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[time-nuts] Osmocom bare PCB's for the LEA-6T.

[Mark Sims]

I got in the Osmocom LEA-6T bare boards from China.   They look good.I have 
a few extras available at $10 each shipped in the US.  Contact me off list.  If 
you need two or more boards, it is cheaper to order them from OSHPARK.COM  You 
can get three for $19.   I put the Eagle .BRD files on OSHPARK.COM shared 
projects  (https://oshpark.com/shared_projects/CZcc5jFa)
If you need a solder paste stencil,  download the .BRD file from OSHPARK.COM  
and send it to OSHSTENCILS.COM  (hint: save a few bucks and don't use their 
default border size, also you probably don't need the back side stencil).  From 
looking at the stencil layer in GERBV, it looks like the openings for the 
LEA-6T module are a bit long and might run into a couple of adjacent caps.  You 
might need to tweak the paste on a couple of the pins.


  
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Re: [time-nuts] Datum 105242-001 pinout

[jimlux]

Sent via the Samsung Galaxy S®6 active, an AT 4G LTE smartphone 
Original message From: bownes  Date: 6/10/2016  8:45 
PM  (GMT-08:00) Tzip Ax SA U ZIP a Academico: Discussion of precise time and 
frequency measurement  Subject: [time-nuts] Datum 
105242-001 pinout 

My Google fu is weak tonight. 

I'm out in the field getting ready for the ARRL VHF/UHF contest. Thought I'd 
bring along the bits for my 10GHz transverter and assemble it during the 
downtime. 

But I'm being thwarted. 

Does anyone have the pinout for  the six pin Datum 10Mhz oscillators?

Thanks! 
Bob
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Re: [time-nuts] ADCs for phase noise measurement

[Richard (Rick) Karlquist]

On 6/11/2016 6:33 AM, Attila Kinali wrote:

Hoi Rick,

use a small uC board to interface with the PC. Saving the samples in
a wav file and using one of the many FFT tools shouldn't be a problem.



This gets even better.  The free Pscope software comes with
FFT.  I don't even need to fool with exporting a .file to
some FFT program.

Rick




Attila Kinali


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[time-nuts] Seek manual for a STARLOC II GPSDO

[cfo]

Group

My Google-Fu has failed me, while locating a manual for a 
Symmetricom Starloc II , not the Starloc II Plus.

If anyone has the manual, and would be kind enough to mail it to me.
Id' be grateful, e-mail size is no problem.

TIA
CFO
Denmark

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Re: [time-nuts] ADCs for phase noise measurement

[Richard (Rick) Karlquist]

On 6/11/2016 6:33 AM, Attila Kinali wrote:

Hoi Rick,

I don't know which phase noise measurement sturcture you are going
to use exactly or what your goals are, so I am guessing here a little bit...


I'm interested in at least 10-100 Hz offset, 1-1000 Hz offset
would be a bonus.  Thus audio is fine on the high end (even 20 kHz
is overkill) but the low end is an issue.


Alternatively, I would suggest using one of the modern sigma-delta
or SAR ADCs, which can deliver increadibly high ENOB and SNR at
astonishing sampling rates. Good candidates might be:

AD7982, 18bit 1Msps
AD7984, 18bit 1.33Msps
LTC2378-20, 20bit 1Msps
LTC2368-24, 24bit 1Msps

Eval boards for these are available (between 100 and 200€) and interface
with SPI. You can either use an USB SPI dongle (between 5 and 50€) or
use a small uC board to interface with the PC. Saving the samples in
a wav file and using one of the many FFT tools shouldn't be a problem.



Good call on the LTC2368-24.  The eval board for it has considerably
better support (like p-scope) than do the Analog Devices eval boards.
I think this might work for me.  What are the tradeoffs between SAR
and sigma-delta ADC?  Can you point me to a few of the "many" FFT
tools?  Maybe I don't have to buy spectrum analyzer software.

Thanks.

Rick




If you don't mind designing your own board, then you can go for something
like the LTC2386-18 which offers 18bit at 10Msps (and still 96dB SNR)
and enjoy a very wide frequency range. But the requirement of LVDS input
might be a killer.


Attila Kinali


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Re: [time-nuts] windows for FFT measurements of phase noise

[John Miles]

> I was thinking more of the sidelobes: if you're looking at a quiet
> oscillator (e.g. -140dBc @ 100Hz) , with a 1 second epoch, and you want
> to measure the noise at, say, 100Hz out, the window function needs to be
> down 140 dB at that bin.
> 
> WIndows like uniform and Hamming are probably only down 50 dB that far out.

The segmented FFT helps with that.  Ideally you have enough segments that 
there's rarely more than 30-40 dB of flatness variation within any one of them, 
which is why HFT95 works well and Hann is still usable.  

Except in the presence of very strong spurs, most of the energy in the 
narrowband segments is going to reside in the first few bins.  It's the HPF 
prior to each FFT stage that keeps that close-in noise from spreading, more 
than the choice of window function.

-- john, KE5FX
Miles Design LLC


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Re: [time-nuts] windows for FFT measurements of phase noise

[Bob Camp]

Hi

> On Jun 11, 2016, at 11:42 AM, jimlux  wrote:
> 
> On 6/10/16 4:09 PM, John Miles wrote:
>>> What sort of windows do folks use for making FFT measurements of
>>> phase noise.
>>> 
>>> Say you have 1 second of sampled data (so the FFT resolution is 1
>>> Hz). If you're interested in the noise power at, say, 10 Hz away,
>>> a rectangular window isn't going to be very far down, unless you
>>> have a LOT of points in the FFT.
>>> 
>>> Grove's paper from 2004 doesn't mention this detail.
>> 
>> As Bob suggests, a multisegment FFT chain is the usual approach.  By
>> the time you're displaying noise down to 10 Hz, you should have quite
>> a bit more than 1 second worth of data to draw from.
>> 
>> For measuring noise the choice of window function doesn't matter very
>> much as long as you correct for the noise bandwidth of the function
>> you use.
> 
> I was thinking more of the sidelobes: if you're looking at a quiet oscillator 
> (e.g. -140dBc @ 100Hz) , with a 1 second epoch, and you want to measure the 
> noise at, say, 100Hz out, the window function needs to be down 140 dB at that 
> bin.

Ummm ….. e … not so much.

If you are looking at phase noise, you are doing it with a system that has 
already taken the carrier out of the picture. 
Either you quadrature lock two oscillators (the 3048 approach) or you do an SDR 
to DC (TimePod) approach. 
The only thing you have to handle is the noise slope in the region you are 
working in. 

Bob

> 
> WIndows like uniform and Hamming are probably only down 50 dB that far out.
> 
> I did find a reference to some Blackman-Harris windows that are pretty wide 
> for the main lobe, but the sidelobes are 100 or 150 dB down.
> 
> 
> 
> However, for spur detection there are major
>> window-dependent differences that need to be considered.  There is
>> only one reference that's worth looking at, and that's the paper by
>> Heinzel, Ruediger, and Schilling.  (Google the authors' names and
>> it'll come up.)
> 
> That's a real nice report.. Excellent
> 
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Re: [time-nuts] ADCs for phase noise measurement (was: windows for FFT measurements of phase noise)

[Bob Camp]

Hi

If you really want to go low noise at the low end, various outfits (TI is one) 
make
ADC’s aimed at geo phone applications. Some do cute things like chopper inputs.
Others approach it without the chopper. Cost is often a bit high. Finding them 
on a
card can be tough. 

There are a number of audio market codec ADC’s that have quite good noise 
performance
up to the vicinity of 90 KHz. You have to be pretty careful about exactly which 
one you get.
They aren’t cheap either.

Bob

> On Jun 11, 2016, at 9:33 AM, Attila Kinali  wrote:
> 
> Hoi Rick,
> 
> I don't know which phase noise measurement sturcture you are going
> to use exactly or what your goals are, so I am guessing here a little bit...
> 
> 
> On Fri, 10 Jun 2016 17:15:22 -0700
> "Richard (Rick) Karlquist"  wrote:
> 
>> I am now putting together a modern homebrew phase noise system.
>> I am planning to use a ZRPD-1 phase detector driven by AMC-123
>> amplifiers.  The phase detector will drive a SpectraDAQ-200 digitizer
>> with SpectraPlus-RT FFT software.  
> 
> From the specs of the SpectraDAQ-200 it looks like they just employ some
> audio codecs for the sampling. This has two consequences major consequeces:
> 1) The performance below 10-20Hz will be bad (yes, they spec the cut of
> frequency as 2Hz, but the audio ADCs are usually not spec'ed below 20Hz).
> 2) Due to the way these ADCs are built, the noise above 20kHz will be
> a lot higher than below (aka noise shaping).
> 
> If this is ok for you and you actually want to use an audio ADC,
> but then I would recommend using one of the USB "soundcards" out there.
> I doubt that the SpectraDAQ-200 is anthing more than an implementation
> of the evalboard circuit with BNC connectors.
> You can get very good soundcards already for 30€. 100€ should already buy
> you one that is about as good as these things can get. The only thing
> you need to have an eye on is, if you need two inputs that the microphone
> input is stereo, which should be the case, but is not necessarily given.
> 
> Alternatively, I would suggest using one of the modern sigma-delta
> or SAR ADCs, which can deliver increadibly high ENOB and SNR at 
> astonishing sampling rates. Good candidates might be:
> 
> AD7982, 18bit 1Msps
> AD7984, 18bit 1.33Msps
> LTC2378-20, 20bit 1Msps
> LTC2368-24, 24bit 1Msps
> 
> Eval boards for these are available (between 100 and 200€) and interface
> with SPI. You can either use an USB SPI dongle (between 5 and 50€) or
> use a small uC board to interface with the PC. Saving the samples in
> a wav file and using one of the many FFT tools shouldn't be a problem.
> 
> If you don't mind designing your own board, then you can go for something
> like the LTC2386-18 which offers 18bit at 10Msps (and still 96dB SNR)
> and enjoy a very wide frequency range. But the requirement of LVDS input
> might be a killer.
> 
> 
>   Attila Kinali
> 
> -- 
> Malek's Law:
>Any simple idea will be worded in the most complicated way.
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Re: [time-nuts] windows for FFT measurements of phase noise

[jimlux]

On 6/10/16 4:09 PM, John Miles wrote:

What sort of windows do folks use for making FFT measurements of
phase noise.

Say you have 1 second of sampled data (so the FFT resolution is 1
Hz). If you're interested in the noise power at, say, 10 Hz away,
a rectangular window isn't going to be very far down, unless you
have a LOT of points in the FFT.

Grove's paper from 2004 doesn't mention this detail.


As Bob suggests, a multisegment FFT chain is the usual approach.  By
the time you're displaying noise down to 10 Hz, you should have quite
a bit more than 1 second worth of data to draw from.

For measuring noise the choice of window function doesn't matter very
much as long as you correct for the noise bandwidth of the function
you use.


I was thinking more of the sidelobes: if you're looking at a quiet 
oscillator (e.g. -140dBc @ 100Hz) , with a 1 second epoch, and you want 
to measure the noise at, say, 100Hz out, the window function needs to be 
down 140 dB at that bin.


WIndows like uniform and Hamming are probably only down 50 dB that far out.

I did find a reference to some Blackman-Harris windows that are pretty 
wide for the main lobe, but the sidelobes are 100 or 150 dB down.




 However, for spur detection there are major

window-dependent differences that need to be considered.  There is
only one reference that's worth looking at, and that's the paper by
Heinzel, Ruediger, and Schilling.  (Google the authors' names and
it'll come up.)


That's a real nice report.. Excellent

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[time-nuts] ADCs for phase noise measurement (was: windows for FFT measurements of phase noise)

[Attila Kinali]

Hoi Rick,

I don't know which phase noise measurement sturcture you are going
to use exactly or what your goals are, so I am guessing here a little bit...


On Fri, 10 Jun 2016 17:15:22 -0700
"Richard (Rick) Karlquist"  wrote:

> I am now putting together a modern homebrew phase noise system.
> I am planning to use a ZRPD-1 phase detector driven by AMC-123
> amplifiers.  The phase detector will drive a SpectraDAQ-200 digitizer
> with SpectraPlus-RT FFT software.  

>From the specs of the SpectraDAQ-200 it looks like they just employ some
audio codecs for the sampling. This has two consequences major consequeces:
1) The performance below 10-20Hz will be bad (yes, they spec the cut of
frequency as 2Hz, but the audio ADCs are usually not spec'ed below 20Hz).
2) Due to the way these ADCs are built, the noise above 20kHz will be
a lot higher than below (aka noise shaping).

If this is ok for you and you actually want to use an audio ADC,
but then I would recommend using one of the USB "soundcards" out there.
I doubt that the SpectraDAQ-200 is anthing more than an implementation
of the evalboard circuit with BNC connectors.
You can get very good soundcards already for 30€. 100€ should already buy
you one that is about as good as these things can get. The only thing
you need to have an eye on is, if you need two inputs that the microphone
input is stereo, which should be the case, but is not necessarily given.

Alternatively, I would suggest using one of the modern sigma-delta
or SAR ADCs, which can deliver increadibly high ENOB and SNR at 
astonishing sampling rates. Good candidates might be:

AD7982, 18bit 1Msps
AD7984, 18bit 1.33Msps
LTC2378-20, 20bit 1Msps
LTC2368-24, 24bit 1Msps

Eval boards for these are available (between 100 and 200€) and interface
with SPI. You can either use an USB SPI dongle (between 5 and 50€) or
use a small uC board to interface with the PC. Saving the samples in
a wav file and using one of the many FFT tools shouldn't be a problem.

If you don't mind designing your own board, then you can go for something
like the LTC2386-18 which offers 18bit at 10Msps (and still 96dB SNR)
and enjoy a very wide frequency range. But the requirement of LVDS input
might be a killer.


Attila Kinali

-- 
Malek's Law:
Any simple idea will be worded in the most complicated way.
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