[aprssig] Kenwood D700 Internal TNC Amazingly Mediocre!

Stephen H. Smith wa8lmf2 at aol.com
Sun Aug 7 00:07:28 EDT 2016

On 8/6/2016 10:19 PM, Steve Noskowicz via aprssig wrote:
> Hold on.  (I know Stephen is quite astute).  However, Keep in mind guys.  This test also
 > depends on the signal transmitted from the digi.  Set up the digi 
differently and you can
 >skew the data.  Perhaps the digi is setup wrong/differently....

There was no digi involved in my test.   I had the FT-1500/TT3 ammo-can 
tracker, equipped with a Diamond 770 no-ground-plane half-wave whip, located at 
the PROPOSED digi site, beaconing direct to my mobile down below.

The purpose was to evaluate whether the proposed digi location could actually 
cover the entire area I need to cover with enough RF. This after playing with 
terrain profiles in Delorme Topo North America in my motel room the night 
before, to select a "magic location" to cover what amounts to two canyons 
joined at right angles.

The discovery of how much poorer the D700's internal TNC was than the 
Soundmodem soft TNC was purely by accident.

On the first drive-test run, the signals from the hill-top beacon to the mobile 
on my selected route down below were very poor, resulting in 
less-than-fully-quieted signals any time I was more than about a third-mile 
from the transmitter.  It was then that I was surprised to see the Soundmodem 
way way out-copying the D700 TNC on these noisy signals.

After wondering why I had so little signal, I returned to the transmit site, 
disassembled the ammo-can tracker, and discovered that a coax cable assembly in 
my tracker box was defective (bad crimp in a commercially-made cable assembly) 
resulting in extremely low ERP.   [Bench-testing the setup at home before the 
trip, I never had the tracker box more than about 25 feet from my mobile so I 
never realized I had 20+ dB loss on transmit! Next time, this thing goes into a 
wattmeter and dummy load before hitting the field...]

I bypassed the bad cable, and re-ran the test.  This time I was getting "full 
smash" completely-quieted signals around the entire 4-mile loop test course. 
The signals were good enough that my even TH-D72 handheld lying horizontally on 
the seat INSIDE the car (no external antenna - just a 19" whip) copied 
virtually every transmission as well.

The result of these investigations is that the difference in the receive 
capabilities of the D700 hardware TNC and the soft TNC will be insignificant in 
the actual application next year. (I have full-quieting signals everywhere on 
the loop with the FT-1500's 40-50 watts out.)

Next year the "magic location" on the hillside will be occupied by an "ammo-can 
digi" containing another FT-1500 mated to a KPC3+ and another Diamond 770 
half-wave no-ground-plane whip.  The current FT-1500/TT3 ammo box tracker will 
be strapped to the shuttle bus.

The 4 receive locations for the digi's downlinks (one at each venue) will each 
be Wouxun KG-UV8D handhelds with 19" whips, mated to the sound input of 
Microcenter 7" "Winbook" tablets running the Soundmodem and mapping software. 
In turn the tablets will be Velcro'ed to the back of 23" HDMI monitors (the 
tablets have a full high-def 1080p HDMI output)  placed at the entrance of each 

The KG-UV8Ds come with a nice drop-in charger with built-in AC supply as 
standard equipment. (no wall wart - just a lightweight 18/2 "shaver" cord) The 
charger holds the radio very stably in a vertical position, making for a very 
compact and tidy receive setup.]   I actually took my TH-D72 inside each venue 
during the drive test, to verify that I have enough RF -INSIDE- each building 
for this modest receive setup to work reliably.
Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page:          http://wa8lmf.net

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