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Building a phase noise measurement system for digital audio
Building a phase noise measurement system for digital audio
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Old 28th August 2016, 06:43 PM   #11
1audio is offline 1audio  United States
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Building a phase noise measurement system for digital audio
I used to use a granite surface plate a pneumatic isolators for phono. Worked well for structure born vibration. But acoustical stuff needs addressing.

You can actively correct for vibration, kind of like a txco or actively suspend the oscillator. Both intersting but nontrivial projects.

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Old 28th August 2016, 11:10 PM   #12
1audio is offline 1audio  United States
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Building a phase noise measurement system for digital audio
Here is the problem detecting acoustic and vibration modulation. The standard tests require long acquisitions which make catching small modulations that may be intermittent difficult. Without a signal in the audio output there can be no effect from modulation so you need a continuous stable signal. Just doing an FFT of that may not see the modulation. What I propose and will try is to generate a continuous tone at something like 3.14 KHz that a wow and flutter meter is sensitive to. Then dig out the meter (buried in storage) and see if sees any modulation. I'm open to easier/better options.
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Old 28th August 2016, 11:45 PM   #13
jborden is offline jborden  United States
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Building a phase noise measurement system for digital audio
Quote:
Originally Posted by 1audio View Post
Here is the problem detecting acoustic and vibration modulation. The standard tests require long acquisitions which make catching small modulations that may be intermittent difficult. Without a signal in the audio output there can be no effect from modulation so you need a continuous stable signal. Just doing an FFT of that may not see the modulation. What I propose and will try is to generate a continuous tone at something like 3.14 KHz that a wow and flutter meter is sensitive to. Then dig out the meter (buried in storage) and see if sees any modulation. I'm open to easier/better options.
Why not just do a phase noise plot with and without vibration isolation?
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Old 29th August 2016, 12:18 AM   #14
1audio is offline 1audio  United States
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Building a phase noise measurement system for digital audio
Simply put I don't know enough about how the noise would show itself. I don't have a phase noise test set. Also it really needs to be tested as a system. The PCB assembly and the casework will all affect the vibration and what happens at the crystal. That's why looking at the analog output seems necessary.
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Old 29th August 2016, 01:31 AM   #15
gerhard is offline gerhard  Germany
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That is so typical for audio, that one of the minor aspects is singled out,
blown up beyond any proportion and that is then the benchmark in a
community. Be it FETs, use of iron in boxes, but in transformers it is ok,
but ferrite is bad again. OMG.

I can assure you that granite does not play a role in commercial oscillator design,
and a good oscillator can deliver stellar performance, just sitting on a lab table
but shielded from moving air.

Vibration sensitivity is a problem when you build a radar for a helicopter
where a crystal is multiplied up to 10 GHz and you get Doppler echoes from
slowly moving targets that are just 5 Hz off the transmitted carrier.

I recommend that from Mr. Driscoll himself:
< http://www.ieee-uffc.org/frequency-c...E_Tutorial.PDF >
including funny oscillators with multiple crystals mechanically rotated by 180...

regards, Gerhard
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Old 30th August 2016, 03:44 PM   #16
xaled is offline xaled
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Not exactly the phase noise measurement information, but a "Crystal Motional Parameters
A Comparison of Measurement Approaches" document. Some very good methods of testing the motional parameters that influence the phase noise.
http://www.cliftonlaboratories.com/D...Parameters.pdf
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Old 24th March 2017, 04:05 AM   #17
jborden is offline jborden  United States
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Building a phase noise measurement system for digital audio
Default HP 3048A Software

I've acquired the hardware for the HP 3048a which, using the 3561a signal analyzer can measure down to 125microHz offsets! The software looks like it can be done a few different ways -- does anyone have experience with software options?:

1) MSDOS 6.0 based on antique hardware
2) HP Basic on ?? -- HTBasic seems really really expensive -- anything cheap available?
3) PM3048 on Windows
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Old 24th March 2017, 11:33 AM   #18
gerhard is offline gerhard  Germany
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MSDOS 6.0 is the least of your problems. There are distribution images
on the net, Microsoft probably doesn't care anymore.

You should try the timenuts group on febo.com. Restoring an
old 3048 will be a most welcome topic there.

Gerhard
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Old 24th March 2017, 07:30 PM   #19
jborden is offline jborden  United States
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Building a phase noise measurement system for digital audio
Quote:
Originally Posted by gerhard View Post
MSDOS 6.0 is the least of your problems. There are distribution images
on the net, Microsoft probably doesn't care anymore.

You should try the timenuts group on febo.com. Restoring an
old 3048 will be a most welcome topic there.
MSDOS 6.0 is no problem, nor building a circa 1990 PC with an ISA HP/GPIB card to run the software. I've got all that.

You've been using an 89441A, right? My question was concerning the different platforms to run the HP software (BASIC or not).

This old equipment is easily obtainable at very attractive prices with just a little patience (or friends with labs ... many times its the PSU which goes bad either due to an old tantalum cap that HP favored at the time, or else a bad diode etc. but the specs on the older equipment are still terrific for lower frequency work ... and that means under a few Ghz.

How are you doing your own programming?

Will certainly check out [timenuts]

On the entirely opposite technology end would be using an FPGA and high speed ADC to do the phase comparisons but looking at the specs, the 3048A might still be unbeatable?
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Old 24th March 2017, 11:46 PM   #20
gerhard is offline gerhard  Germany
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On my daytime job we have a E5052B and another project member
has a R&S FSUP (?) which gave nearly identical results. I'd like
to keep that capability for myself, at least for some fixed frequencies
like 5, 10, 100 MHz. (being a free lancer)

I use the 49441A currently as an FFT analyzer after preamplifiers of
my own for baseband; I'm still stuck at 190pV/rtHz or so, already too
good after ring mixers, but I'd like to break the 100 pV barrier.... It eats
up lots of time.

I control the 49441A over the LAN. It took a BNC-LAN to twisted pair
converter for $25, but it works really good. I just open port 5xxx on
192.168.1.111 and feed it GPIB commands and read the results.
I completely ignore its GPIB interface for the finger-thick cable, no
trouble with gpib drivers, AT/PCI-Bus cards and such, had enough of
that 30 years ago.

I think my 89441A has the BASIC option, but I just use it to generate
data and do the FFTs, after that I process the data myself. For me,
BASIC is a dead end, I write my stuff in C; that is probably portable
to the end of time, at least my time. I don't know if the 3048 has
a LAN interface; if it has you can get my sources as a template to
make it work.

One of the beta testers of my preamp has a working 3048, he uses
it at least for baseband measurements. I could pass him your email
address if you want. Personally, I don't have much interest in restoring
a 3048; some of the people who used to use it ( in my daytime job
environment) said it was really cumbersome, and I value their opinion.

But then if your work is putting satellites into space, the pockets are
much deeper and your perspective quickly adjusts to that.

I have a ADC / FPGA / DSP project with 2.4 GHz sampling rate
on the back burner, have done similar things but I must first
flush the pipeline.

I have been killing a few trees around my house with a chain saw today
and put two of them into a container; I'm pretty well done for today.
My back hurts. Not the appropriate job for someone who is used to solder
under the microscope.

regards, Gerhard
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Last edited by gerhard; 24th March 2017 at 11:59 PM.
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