[aprssig] What is "TNC Channel Switching"?

Andrew Pavlin AndrewEMT at hotmail.com
Fri Apr 11 08:42:13 CDT 2014

Could one then presume that such TNC's could not participate in any binary radio network (such as TCP/IP over AX.25 or OpenTRAC), since the binary payload might contain those characters?

Seems kind of archaic, especially with KISS having a means to send such commands without reserving byte values in the data stream.

Andrew, KA2DDO
Sent from my Verizon Wireless BlackBerry

-----Original Message-----
From: Steve Dimse <sdimse at gmail.com>
Date: Fri, 11 Apr 2014 09:33:46 
To: AndrewEMT at hotmail.com<AndrewEMT at hotmail.com>; TAPR APRS Mailing List<aprssig at tapr.org>
Subject: Re: [aprssig] What is "TNC Channel Switching"?

The KAM Plus was a dual band TNC, so one serial port could give you access to two radios at the same time, generally HF and VHF. It also could automatically gate between the two. I think the same scheme was used on the 9612 which was 1200 and 9600 baud simultaneous. The stream switch would tell the TNC which band to send a packet. I don't recall if they listened for stream switches from the RF side. You definitely should not send them on a serial port unless you have a way to disable it or unless you state your code is incompatible with the KAM and KPC 9612. There still are some floating around. Generally, best to follow the spec on things like this. 


Sent from my iPhone

> On Apr 11, 2014, at 9:23 AM, Andrew Pavlin <AndrewEMT at hotmail.com> 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
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> aprssig at tapr.org
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