[aprssig] Soundcard Packet Analyzer
Stephen H. Smith
wa8lmf2 at aol.com
Sat Oct 22 21:44:59 CDT 2011
On 10/22/2011 7:20 PM, Bob Bruninga wrote:
> What we really need is a PACKET ANALYZER software!
> Mike Chesena, KA2ZEV suggested something like this.
> I think it is a GREAT idea!
> Do we have any DSP jockies that can write this code? Or probably most of it alreayd exists somewhere. But the self-calibration will be important so we are all comparing to the same orange.
> Bob, WB4APR
You can achieve something close to this with three off-the-shelf Windows
applications together NOW, with no DSP code needing to be written.
1) The well-known AGW Packet Engine is a 300/1200/9600 baud KISS TNC
entirely in software that will run on most sound systems. AGWpe has an
internal "tuning aid" display that can create an audio spectrum analyzer
display, a waterfall (time domain spectrum analyzer) display similar to most
PSK programs, and perhaps most importantly, a simple oscilloscope display that
can clearly display the relative level of the the 1200 and 2200 Hz tones (and
the relative level of different users' bursts).
2) The companion freeware program "AGW Monitor" automatically connects to
AGWpe's TCP/IP output when started, with absolutely no configuring or tweaking.
It creates an on-screen display similar to the MONITOR mode of most classic
TNCs with the header information (callsign, path, destination, etc on one line
and the packet payload on a second line. (Or alternatively, you can point any
web browser to localhost:8000 and view the same info via AGWpe's built-in
internal web server output, along with useful stats such as a MHEARD list of
stations that shows how many times each one has been heard.)
3) The third application (and second sound card app) is the absolutely
amazing Visual Analyser 2011. This *FREEWARE* program, written by an
Italian electrical engineering PhD candidate at the University of Rome,
emulates a whole stack of HP audio test instruments in a single 5 MB exe file.
. From the sound card record input(s), Visual Analyzer creates a dual-trace
audio scope with adjustable triggering, a dual-trace audio spectrum analyzer,
an audio frequency counter, an audio voltmeter that can display in either
millivolts, or dB similar to a "VU" meter, a phase meter (if you have the same
tone freq in both channels) and a harmonic distortion meter. All these
parameters can display in separate windows at the same time from an audio input.
. At the same time, it can create a dual-tone audio GENERATOR, an audio
sweep generator, a function generator (sine, square, triangle,etc) or a pulse
generator with fully configurable pulse duration and repetition rate on the
PLAYBACK (output side) of the sound system, assuming that the sound card is
capable of full duplex operation. Finally with a few simple external circuit
components, the program can become a ZRLC bridge!
The spectrum analyzer is capable of linear or log display on either the X-axis
(audio frequency) or Y-axis (amplitude). In the default, mode, the Y-display is
log (expressed in dB) and is limited only by the dynamic range and noise floor
of your sound card. Even a crap bottom-of-the-line sound system should be able
to display a 50 dB dynamic range, and a GOOD one 90-110 dB. A zoom slider lets
you expand the display to a much smaller dB range on the Y-axis, to the point
where you can easily see tone skewing of only a dB or two, or accurately
measure the noise floor of a radio 20-30 dB below peak deviation. By default,
the spectrum display X-axis is a 3-decade 20 Hz to 20,000 Hz log presentation,
but it can be switched to linear and over a specified min and max range. For
normal radio response testing, I set the display to 200Hz-5000Hz linear. The
scope/analyzer has switchable custom high-pass and low-pass filters that can
keep low frequency components like PL or DCS from producing "ripple" on the
display of higher frequency tones, or to remove hiss-induced "grass" from
off-the-air monitoring of weak signals.
"Out of the box", the program displays relative values referenced to the
minimum and maximum counts of the sound card A-D converter. The program has
provisions for being calibrated against a known external audio source with the
results made permanent in a .ini file. The Visual Analyzer scope and analyzer
can then display absolute audio millivolt and dBm values.
I hacked a Bearcat 760 scanner and tapped the output of it's discriminator,
wiring it to the existing "Tape Recording output mini-jack on the back panel .
In turn, I attached the audio input of my iMic external USB sound card (Click
Here for review of this device on my web site <http://wa8lmf.net/ham/imic.htm>)
to the Bearcat's discriminator, and calibrated the pair with my IFR-1500
service monitor. Using the external sound system lets me move the assembly
from one PC to another without having to re-calibrate it each time. [Note
that the 6-pin mini-DIN "DATA" or "PACKET" jack on many FM-capable radios will
provide the same kind of raw non-de-emphasized discriminator output for these
kinds of measurements.] The Bearcat/iMic pair now serves as a quite usable
deviation meter and signal monitor.
Looping the sound card audio generator output back into one channel of the
sound card scope input lets you do very precise lissajous-figure frequency
measurements on received PL tones, DTMF tones, TNC mark/space tones in CAL
mode, etc fed into the other sound card input channel.
It is not too well known that since Windows XP, it is possible to have more
than one program accessing the sound system simultaneously. I routinely run
mmSSTV (analog SSTV), EasyPal ("digital" SSTV) and AGW Packet Engine off the
same sound card at the same time in my APRN (combined SSTV and APRS) setup.
In a similar manner, I run Visual Analyser (for a closeup view of the wave
forms) and AGWpe (to display the packet information) simultaneously. About
the only thing I can't measure exactly is the TXD, but as you have pointed out,
this can be easily guessed at by ear.
AGW Packet Engine (Free Version)
AGW Monitor Companion to AGWpe
Visual Analyzer 2011 Information
Visual Analyzer 2011 Download
Stephen H. Smith wa8lmf (at) aol.com
=== Now relocated from Pasadena, CA back to 8-land (East Lansing, MI) ===
Home Page: http://wa8lmf.net
===== Vista & Win7 Install Issues for UI-View and Precision Mapping =====
*** HF APRS over PSK63 ***
"APRS 101" Explanation of APRS Path Selection & Digipeating
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