[aprssig] Kenwood "TC" command

[Stephen H. Smith]

On 6/15/2011 2:16 PM, Lynn W. Deffenbaugh (Mr) wrote:
> Are you saying that sending an APRS message that happens to contain the text 
> "TC 0" or "TC 1", Kenwood radio TNCs will freak out?   Does this happen only 
> in "host" (CONVerse) mode or KISS or both?

[The D700 and TH-D7  single main serial port is shared between TNC send/receive 
data, and radio control functions (TNC on/off,  TNC parameters, PL tone, 
frequency settings/queries, memory load/readouts, etc) depending on the APRS 
mode the radio is in.]


The TNC would have to be in "PACKET" mode and  toggled to COMMAND mode with 
^C.    In CONV mode everything sent into the serial port from the external 
terminal or app is taken as text to be transmitted.   (Rather than commands to 
acted on by either the TNC's interpreter or the radio's interpreter).      If 
the TNC is either in "PACKET" COMMAND mode, standalone "APRS" mode, or turned 
off completely, then inadvertently sending "TC 1" or "TC 0" into the shared 
serial port of these radios could be taken as TNC power on or off commands.



The D700 and TH-D7 are notorious for a too-small buffer that overflows in KISS 
mode, since the entire raw packet including headers, etc lands in the buffer 
before being passed to the external terminal, (rather than just the packet 
payload as it does in the standard command-line mode).    The problem is 
aggravated by high traffic rates on the RF channel, especially if a lot of 
longish packets such as raw NMEA posits or weather station data are present.

[ The direct predecessors of the D700 and TH-D7 were originally designed for 
the Japanese "NaviTra" ("NAvigation TRAnsceiver") system.  When these designs 
flopped in the domestic Japanese ham marketplace, the hardware was  re-purposed 
for APRS, with new firmware.     The APRS implementation is a firmware kludge 
crammed into a microcontroller with too little RAM and too little ROM to do it 
properly. ]


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Stephen H. Smith    wa8lmf (at) aol.com
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