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[aprssig] "Best" packet decoder solution

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Mon Dec 27 16:14:47 UTC 2010

On 1200baud AX.25 on 2m, I've compared TT4, OT2m, T2-135, D7, and AGW's 
PEpro and the hands-down winner was...

PEpro, but then, it has an entire sound card and computer to assist with 
the signal detection and decoding.

The DSP-based TT4 I run as my IGate (KJ4ERJ-7/KJ4ERJ-1) does very well 
for properly deviated packets.  With the RXAMP tuning I'm running in it, 
it is deaf to under-deviated (quiet) packets.  I've found that the TT4 
doesn't like to decode back-to-back packets.  I'm not sure if the 
timeslicing between the decoder and the PC interface causes trouble, or 
if there's a single-buffer somewhere in the decoder chain, but if a 
remote station of digi blasts out two or more packets, the TT4 seems to 
consistently miss the second one.

The OT2m/T2-135 use a hardware docoder chip that works quite well.  I 
run it mobile with a Nuvi-350 display as KJ4ERJ-9 and sometimes IGate it 
through APRSISCE on my Windows Mobile phone as KJ4ERJ-12.  My original 
T2-135 was stone deaf, but was swapped out for one with some audio 
filtering that dramatically improved its decoding ability.

When I had AI4GK's Kenwood D7 running as an IGate, it was decoding some 
packets that the TT4 missed, but missed some packets that the TT4 
decoded.  It handled back-to-back packets MUCH better than the TT4.  I'd 
place it just above either the TT4 or the Tracker2 family, only based on 
more packets decoded, but it still didn't decode the sum of all packets 
seen by the TT4/Tracker2 put together.  In other words, it still missed 
some packets.

AGW's PEpro running on a Windows 98 laptop decoded the most of any 
1200baud AX.25 solution I've played with.  IIRC, it decoded 100% of any 
of the 3 hardware solutions.  There were still some packets that I could 
hear by ear that didn't decode, but remember, a single bit error 
anywhere within the packet will cause that.

Anyone else done any side-by-side comparisons that they can share? 

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

Greg Clark wrote:
> What's the "best" packet decoder out there?
> By "best", I mean the one that has the greatest ability to decode APRS 
> data packets.
> Can be stand-alone (like the D710) or separate unit (like Kantronics TNC)
> Is any one in particular considered the  "gold standard" ?
> How do units like the new Kenwood HT, or small inexpensive ones like 
> the TT4/OT/TNC-X  compare?
> -- Greg K7RKT
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