Open Two Radio Switching Protocol

The Open Two Radio Switching Protocol (OTRSP) is a simple set of commands and events for computer control of a Single Operator Two Radio (SO2R) device.


The first SO2R control was developed for logging prorams such as CT, TRLog, and NA.  These programs were MS-DOS based. They used LPT port pins to generate CW and to control the SO2R devices.

Since then, two things have happened.  One is that Windows NT and successor products made it more difficult to use LPT pins.  It seems Microsoft thought the LPT port should be used for printers.  Third-party drivers were required for a program to be able to access the printer port directly.

The other is that the LPT port itself has become obsolete. Almost no printers built today even have an LPT port, and many computers no longer have one. USB is less expensive and it does more.

However serial ports are still viable. Although many computers do not have them it is easy to convert USB to serial in ways which are suitable for use with an SO2R box.

The OTRSP protocol was developed for the YCCC SO2R Box.  It is available in N1MM Logger as of version 9.8.5, WriteLog as of version 10.73, and  Win-Test as of V4.4. And it can be used by anyone who wants to write a logging program or to build an SO2R device.

Implementing OTRSP in a Logging Program

A minimal implementation of OTRSP is very simple.  The logging program must send a few command strings to the SO2R device. This is described in the OTRSP specification which can be downloaded from this page. There is also a reference OTRSP SO2R device program which can be downloaded and used to test logging programs.

Implementing an OTRSP SO2R Device

There are two ways to implement an SO2R device using OTRSP.

One way is to have the device itself understand OTRSP. The protocol is simple enough it can be implemented in just about any microprocessor which can handle serial data at 9600 baud.  This is the method used in the PIEXX SO2RXlate and the SO2RDuino.

The other way is to have the SO2R device understand a different protocol and use a program on the PC to handle OTRSP.  THis is the method used in the YCCC SO2R Box.


Protocol Specification

The current protocol version is 0.9. This version adds text which mentions TCP/IP as a transport for OTRSP.

The protocol is not expected to change in any incompatible ways in the future. However the specification may be rewritten for clarity.

Reference SO2R Device

This is a program which understands the OTRSP protocol.  It doesn’t do much except to show the commands and their effects, but it is useful for implementing OTRSP in a logging program. It is version 1.1.0. It supports the extension which handles more than two radios, in this case handling four.  It does not currently support the voice keyer or non-COM port extensions but it understands all other OTRSP commands. There are no known bugs.