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: [email protected] [mailto:[email protected]]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
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--
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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