[time-nuts] Sound Card Spectrum Analyzer

Fri Feb 19 01:27:37 UTC 2010

You could also consider whether Gnuradio (http://www.gnuradio.org) could 
do what you need.  It has interfaces to the Linux sound system.

John
----

Bob Camp said the following on 02/18/2010 08:10 PM:
> Hi
> 
> Ok, A bit more info:
> 
> 1) Quadrature PLL using an RPD-1 DBM and a home brew lock box. 
> 2) Willingness to accept that I'm measuring a pair of oscillators
> 3) Plenty of sources at the appropriate frequencies
> 4) First took a shot at this in 1975 (I forget the Fluke app note number ...) been doing it ever since
> 5) Appropriate preamp between the RPD and sound card is a work in progress
> 6) Sound card is a 192 KHz / 24 bit / ~110 db snr class card
> 7) Sound card will get butchered for the application.
> 8) Should be able to hit -165 ish floor, -120 ish at 1 Hz
> 
> Except for the 16 bit limitation, Baudline looks like it's got what I need.
> 
> Bob
> 
> 
> On Feb 18, 2010, at 7:53 PM, John Miles wrote:
> 
>> Unfortunately there's no way to build a sound-card application that can
>> measure phase noise in the general case without a lot of additional
>> hardware.  Baseband PN analysis with an FFT presupposes that you have some
>> external means of downconverting the DUT signal to DC with a superior
>> reference at the same frequency, tuned with a quadrature PLL.  There must be
>> a suitable high-pass filter and LNA to block any DC residuals and preamplify
>> the remaining part of the noise sideband.
>>
>> Further, it's often the case that noise close to the carrier is strong
>> enough to keep you from being able to use enough gain to see the broadband
>> floor, so you actually need more than one high-pass filter ahead of the
>> sound card in many cases.  These switchable filters were mandatory with the
>> old 13-bit signal analyzers like the 3561A, and may still be needed today if
>> you want to look down to 1 Hz.  If you restrict your offset range to (say)
>> 100 Hz to 20 kHz and require a 24-bit sound card, you can probably get away
>> without the switchable HPFs.
>>
>> It'd be helpful to know exactly what sorts of measurements you need to make,
>> and on what devices.  PN measurement is a *lot* of work, on both the
>> software and hardware sides.  Much of it goes into developing a suitable
>> calibration process.  Take a look at the 3048A manuals sometime, realizing
>> that the 3048A hardware itself is not very complicated...
>>
>> -- john, KE5FX
>>
>>> -----Original Message-----
>>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
>>> Behalf Of Bob Camp
>>> Sent: Thursday, February 18, 2010 4:18 PM
>>> To: Discussion of precise time and frequency measurement
>>> Subject: Re: [time-nuts] Sound Card Spectrum Analyzer
>>>
>>>
>>> Hi
>>>
>>> Both are very cool programs. Both are full of all sorts of neat
>>> features. As far as I can see, neither one has the features I'm after.
>>>
>>> More or less - I want it to run like a clunky HP audio analyzer
>>> rather than a very cool tool for ham radio.
>>>
>>> Bob
>>>
>>> On Feb 18, 2010, at 6:33 PM, Don Latham wrote:
>>>
>>>> You have looked at:
>>>> spectran and spectrum lab ?
>>>> Don
>>>>
>>>> Bob Camp
>>>>> Hi
>>>>>
>>>>> Assuming I have a decent sound card, and a computer, the next
>>> thing I need
>>>>> is software. If I want:
>>>>>
>>>>> Required:
>>>>>
>>>>> 1) non- commercial
>>>>> 2) 1 Hz normalization
>>>>> 3) good low frequency processing (decimation ahead of the fft)
>>>>> 4) low cost
>>>>>
>>>>> Much preferred:
>>>>>
>>>>> 5) a non-evil OS
>>>>> 6) Rational performance on a non-quad core system
>>>>> 7) free
>>>>> 8) rational calibration
>>>>> 9) scope view.
>>>>> 10) reasonable graphics
>>>>> 11) active support by the author
>>>>>
>>>>> The application is measuring phase noise. That what makes 2 &
>>> 3 pop up on
>>>>> the list.
>>>>>
>>>>> I've looked at a lot of programs and they all seem to be
>>> pretty slick. The
>>>>> ones I've looked at so far don't quite hit the mark for phase
>>> noise. I'm
>>>>> pretty sure that there are others on the list who have dug
>>> into this same
>>>>> issue already.
>>>>>
>>>>> Bob
>>>>> _______________________________________________
>>>>> time-nuts mailing list -- time-nuts at febo.com
>>>>> To unsubscribe, go to
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>>>>> and follow the instructions there.
>>>>>
>>>>
>>>> --
>>>> Dr. Don Latham AJ7LL
>>>> Six Mile Systems LLP
>>>> 17850 Six Mile Road
>>>> POB 134
>>>> Huson, MT, 59846
>>>> VOX 406-626-4304
>>>> www.lightningforensics.com
>>>> www.sixmilesystems.com
>>>>
>>>>
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>>
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> 
> 
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