[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
EchoLink: Node # 14400 [Think bottom of the 2-meter band]
Home Page: http://wa8lmf.net
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