[aprssig] Alinco or ???

Stephen H. Smith wa8lmf2 at aol.com
Thu Nov 10 03:01:34 CST 2005

scott at opentrac.org wrote:

> .
>Did some more tweaking on my board and copy is much better now, at least
>with the test source.  Real-world performance is still lacking.  Hey,
>WA8LMF, are you still out there?  Did you ever get that test CD of APRS
>traffic made?  Would be nice for performance testing.

I'm currently in my home town of East Lansing,  MI visiting my mother 
and sister who still live here.  I've got two of the three tracks 
completed. The third one (A half-hour recording of my D700 mobile 
alone,  beaconing every 10 seconds,  on a non-144.39 channel as I drive 
about a 10-mile loop that should take me from hard quieting to fringe 
flutter and multipath) will be finished as soon as I get back to L.A. 
around the 21st of this month.    

The project got delayed because of an unexpected change of cars.   I had 
to strip my entire mobile shack (FT-100, TM-742, D700, mobile SSTV 
LiveCam, laptop, etc) out of my old Passat TDI turbodiesel.  I just 
finished relocating everything into my new Prius two days before 
departing on this trip.  [I hadn't expected to get the Prius for another 
2 or 3 months...]

The first two cuts of the TNC Test CD are resting on this very laptop I 
am writing on right now.   

One is a clean strong signal recording of a single packet from my D700 
beaconing taken directly off the low-distortion discriminator of my 
IFR-1500 and then duplicated 100 times in the CoolEdit audio editor.  
The intent is to use this recording to modulate an RF signal generator 
while varying the RF output level to characterize TNCs as the RF level 
becomes less than fully quieted.      Since I have exactly 100 identical 
Mic-E bursts on this track, it will be easy to compute the failure rate 
in percent by counting the number of decoded packets through a given TNC 
at a given RF level.

The second is a recording off-the-air,  from the discriminator of an 
FT-1500,  of the "carnage" on 144.39 during the peak of the afternoon 
commuter rush in L.A. .   It includes a wild variety of under and 
over-deviated signals, collisions with signals on top of each other,  
digipeaters clobbering each other, etc.  I have edited out nearly all 
the quiet spots so the longest period of non-activity is less than one 
second in order to challenge buffers in TNCs and programs.  By removing 
most of the dead spots, I was able to fit over half an hour of real-time 
activity into only 15 minutes of recording.   My assumption is that this 
one would be played back as audio directly directly from a CD player or 
CD-ROM's audio jack,  into a TNC - not via modulated RF. )

The third one will also be recorded from the FT-1500's discriminator as 
I make the test run around midnight to minimize the chance of other 
signals on the channel during the test.    

#2 and #3 are recorded open-squelch so there is unquieted discriminator 
white noise between bursts to test software DCD if desired.   All are 
recorded "flat" directly off the discriminator.  If you want to simulate 
audio taken from the speaker (i.e. de-emphasized) you can cobble in your 
own RC de-empasis network at the output of the CD player.

I will be putting this stuff up in standard audio CD  [not as MP3s or 
WAVs on a CD-ROM] so the samples will be in full lossless 44.1K CD 
audio.   Another advantage of using CD audio rather than WAVs on a 
CD-ROM is that you can play it back on an old junker CD-ROM drive 
stand-alone, via the earphone jack,  without needing a computer. 

Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com

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