[aprssig] What is "TNC Channel Switching"?
Stephen H. Smith
wa8lmf2 at aol.com
Fri Apr 11 08:42:43 CDT 2014
On 4/11/2014 9:23 AM, Andrew Pavlin wrote:
> Greetings, all.
> I was slogging through the APRS spec, and came upon a mention that the ASCII characters '|' and '~' were reserved for TNC channel switching, and couldn't appear in any messages or even as a symbol code.
> What does this mean, and is it still applicable? Will I break the APRS-IS or some ancient TNC somewhere if I send those characters in an APRS message?
> Just curious.
> Andrew Pavlin, KA2DDO
> Sent from my Verizon Wireless BlackBerry
> aprssig mailing list
> aprssig at tapr.org
There are some classic serial-port-interfaced TNCs that actually have two
separate modems in a single box connected to a single serial port.
Notably the Kantronics "KAM" (Kantronics All Mode) which combines a 300-baud
multimode HF modem and a 1200-baud VHF packet-only modem. The Kantronics 9612
combined a 1200-baud packet modem similar to a KPC3 and a 9600-baud packet
modem into a single box. In either case, the two modems can be connected to
two separate radios and operated simultaneously via a single serial line
to/from the PC.
Commands typed from the PC console were prefixed with either the "pipe" symbol
or the tilde to indicated which of the two modems you wanted to send commands
(or text to be transmitted) to.
In the heyday of conventional packet, numerous third-party programs were
developed that "covered up" this clumsy command-line interface by providing
split-screen interfaces and/or "Radio1"/"Radio2" function key mappings to the
user that handled the "stream" switches for you.
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