It’s been about six months since I’ve had time to work on the SO2R controller. I know there are several out there who are interested in this unit so I’ve created this page to keep you updated on my progress. I’ll add to it as things move along.


January 23, 2023

I’m taking a slightly different approach on the SO2R controller than what I published back in July 2022. With the new Mini+ there’s no reason to have the function keypad on the SO2R controller so I’ve been able to ‘shrink’ the package down a little (I guess). Instead of using the PacTec KEU-7 sloped enclosure (7″ x 5″ x 3″) the new design will fit in a PacTec CM6-225 enclosure (6″ x 6.25″ x 2.5″). This is a conventional equipment case and the new design will feature the front panel PCB shown in the lead photo along with a main PCB containing the logic, amps, and switching matrix in the box. A back panel with the connector cutouts and labeling will also be included in the PCB kit. This will allow the controller to sit on one of your radios or on a shelf and not take up valuable desk space.

The connection scheme will be much simpler than what I presented originally. Here’s the block diagram for the new design:

CTR2-Mini SO2R Controller v2.0

In a nutshell, each Mini connects to the SO2R controller using two 3.5mm (1/8″) stereo cables and a CAT5 cable. The SO2R controller will route the control signals from the selected Mini to the selected radio’s I/O interface using a single CAT5 cable. The new radio I/O interface, called the CTR2-Audio I/O is based on the Radio I/O modules I built for the original CTR2 controller but use 3.5mm stereo jacks for the radio connections instead of the 12-conductor terminal block. Two audio I/O modules bring audio to and from your radios to the SO2R controller in addition to delivering Key, PTT, and CAT signals from the Mini. Your PTT or straight key, paddles, two mics, and headphones connect to the controller and are automatically routed to the selected Mini and radio when you select a radio on the controller.

A separate connection will bring Tx and Rx audio from the selected radio out of the controller to a USB sound card interface on your PC.

Linking the two Minis together via WiFi allows you to synchronize both radios to the same frequency for true receiver diversity or have each radio tuned to a different band and tune them both with either Mini or either radio’s tuning knob. When the radios are synchronized on the same frequency, selecting either radio for transmit automatically causes the other Mini to tune it’s radio 10 MHz away from the synchronized frequency. Also, if the Mini’s are linked to the CTR2-Antenna Switch Controller the controller will automatically open the antenna to the offline radio when the other radio is transmitting to minimize the amount of RF presented to the offline receiver.


For those that don’t need the functionality and instant switching of full SO2R control, a new CTR2-Mini Audio Controller will be available that allows you to share mics and a headset with multiple radio. When paired with the new CTR2-Mini Radio I/O Multiplexer and Audio I/O modules you can select up 16 radios to control by just selecting a Radio Port on the Mini. The block diagram below shows this configuration.


I’ll update this page as I make further progress on the SO2R controller. As always, let me know if you have any suggestions for improvement. This is the time to add them!

73, Lynn, KU7Q