[aprssig] Kenwood D700 Internal TNC Amazingly Mediocre!
Stephen H. Smith
wa8lmf2 at aol.com
Fri Aug 5 22:53:34 CDT 2016
I had always assumed that the built-in TNC of the D700 was fairly optimized,
due to being mated directly to the radio's discriminator, avoiding audio
channel distortion, audio level issues, squelch rise times, de-emphasis issues,
I just got back from a road trip to the Colorado Rockies for the annual
Evergreen Jazz Festival. While there, I did some coverage testing in the
mountains around Evergreen of a potential portable digipeater and tracker for
the festival shuttle bus, that may be used next year.
This is very rugged mountain terrain with few line-of-sight paths and lots of
multipath. I used the D700's internal TNC with one copy of UIview on my
Panasonic CF-51 mobile Toughbook.
I also connected the 6-pin mini-DIN "data port" of the D700 through one of my
homebrew sound card interfaces to a Behringer UCA-202 external USB "soundcard".
In turn, the UCA-202 was used by the UZ7HO Soundmodem software TNC. The
Soundmodem was linked to a second copy of UIview running on the same computer.
(The Soundmodem faithfully emulates the AGW Packet Engine interface supported
by most current APRS clients.)
The tests consisted of placing my FT-1500/TinyTrack 3 ammo-box tracker at the
hillside location I picked for the digipeater, based on radials I drew on
Delorme TopoUSA. The tracker was set to beacon every 20 seconds on 144.37 MHz.
I then drove the 4-mile loop route taken by the shuttle bus during the event.
[The original intent of using the soft TNC on the mini-DIN port at all was to
try using 300-baud HF-style packet on VHF/FM to gain 3-4 dB of noise margin
compared to 1200 baud.]
I was completely shocked at the difference between the D700's hardware TNC and
the software TNC, both at 1200 baud. When the signals were clean and
fully-quieted, there was essentially no difference between the two TNCs. When
the signals fell out of full quieting, or were "fuzzed up" with multipath
distortion, the Soundmodem massively outperformed the D700 internal TNC.
Driving the 4-mile winding loop around Evergreen, only about a third of the
loop showed on the D700 hardware TNC, while 100% of the beacon transmissions
showed on the instance of UIview linked to the Soundmodem soft TNC.
When I saw how well the Soundmodem worked at 1200 baud, I abandoned the idea of
going to 300 baud for this project. (Staying at 1200 means I can intermix
off-the-shelf 1200-baud TNCs, radios and soft TNCs, while 300 baud would
require that every node involve a PC of some sort running the 300-baud software
Stephen H. Smith wa8lmf (at) aol.com
EchoLink: Node # 14400 [Think bottom of the 2-meter band]
Home Page: http://wa8lmf.net
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