[aprssig] Kenwood D700 Internal TNC Amazingly Mediocre!

Robert Bruninga bruninga at usna.edu
Sat Aug 6 10:42:10 CDT 2016


I think what this demonstrated was not a lack of performance of the D700
but a lack of a match between the modulation of the tiny track and the D700,

I have found the D700 to be the best performer when used with the other
kenwood radios. IE, they match the receiver to the transmitted waveform.
So performance between kenwoods is the best baseline or benchmark I haven't
found anything that can beat it.  THen they decode all the way down to the
FM threshold.

This test demonstrated what we all know. and that is packet is carried on
an analog channel and performance will never be good  unless all the analog
parameters match the channel.  It is amazing to see some of the signals on
the air how badly they are modulated...

Two kenwoods will decode down to 3 bars.
Bob


On Fri, Aug 5, 2016 at 11:53 PM, Stephen H. Smith via aprssig <
aprssig at tapr.org> wrote:

> 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, etc.
>
> 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 Soundmodem.)
>
> ____________________________________________________________________
>
>  Stephen H. Smith    wa8lmf (at) aol.com
> Skype:        WA8LMF
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