[aprssig] Kantronics MT1200G

Stephen H. Smith wa8lmf2 at aol.com
Tue Dec 11 03:15:58 EST 2007

Alan M Fudge DVM wrote:
> I have Kantronics MT1200G- purchased this spring with intention of 
> APRS/digipeating with search and rescue and also packet for emergency 
> ham comm. After no response from email and fax from Kantronics 
> support- I finally got around to phoning for helpful support for com 
> setup
> Forgive me for calling the comm protocols as archaic, but as a mostly 
> Mac user (but purchaser of Vista laptop for SAR mapping, comm, and ham 
> stuff), and with Hyperterminal Private Edition installed, I am 
> struggling to understand the manual for the correct string to beacon 
> APRS via a HT or mobile an the MT1200. I am reading other packets but 
> probably don't fully understand the manual.
> this is the string I have for GTEXT: 
> -is that correct? Any errors?
> Alan M Fudge DVM
> El Dorado Sheriff Search and Rescue, California
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1)     A "Vista laptop" is just about the worst possible choice for APRS 
applications.  Any such laptop most likely does not have any real 
physical serial COM ports that are essential to most APRS applications 
involving computers, GPS and TNCs.    You will be forced to struggle 
with the USB-to-serial converter cable "dongles", many of which 
imperfectly emulate a real serial port, lack proper driver support for 
Vista, or simply don't work with particular applications.   Some will 
work, but it's far far less hassle to have a real serial COM port in the 
first place.

2)     Any tracker derived from a TNC like a KPC3 will be a very dumb 
tracker tracker inefficiently transmitting raw NMEA strings over the 
air,  that are over 10 TEN TIMES longer than the compressed Mic-E format 
posits generated by a TinyTrak or a Kenwood D7/D700/D710 in it's native 
mode.   These longer strings are far more likely to NOT be received 
successfully since there is a far greater chance that the packet will be 
hit by mobile flutter, a pop of noise or get stepped on by other 
stations.   Further they needlessly occupy more air time on busy APRS 
channels than necessary.   

3)     Note the description of this device as a "Wireless Modem" rather 
than a "TNC".  This is the tip-off that this device is primarily for 
commercial land-mobile NON-HAM applications. The MT-1200 is primarily 
intended for commercial AVL (Automatic Vehicle Location) and telemetry 
using proprietary protocols.  It only makes a token concession to ham 
standard operation, primarily for classic "connected" packet rather than 
APRS operation.   

It only supports basic "dumb" digipeating without the duplicate packet 
suppression and WIDEn-N callsign substitution digipeating characteristic 
of modern APRS operation.  It would be capable of simple WIDE1-1 
first-hop home fill-in digipeating.  It would not be able to function as 
a  modern mountain-top WIDEn-N digi in standalone mode

The easiest way to make this thing behave as a fully-functional 
digipeater is to let a program like APRSplus or UIview running on a PC 
place the TNC into KISS mode, bypassing it's slightly non-standard 

4)    The GPS in this unit is a rather dated unit not using the modern 
high-sensitivity SiRF III chipset or equivalent. 

I've always though embedding the active RF circuitry of of a GPS 
receiver in some other device's box (like a transceiver or TNC) is a 
rather perverse concept since it then forces you to deal with the 
horrendous coax losses at 1.6GHz to get from the external antenna to the 
GPS.  Not to mention having to deal with fabricating coax cable 
assemblies with those nasty subminiature connectors like SMAs or SMCs 
that GPS receiver modules and patch antennas use.  

It makes much more sense to combine the patch antenna and GPS receiver 
electronics (like a Garmin GPS18 or the low-cost Deluo units) into a 
single unit and then run DC power up/serial data down to the other 
device, avoiding the coax loss and miniature RF connectors.    I.e.  a 
Garmin GPS-18 all-in-one plugged into a TinyTrak or Kenwood serial port.


Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
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