SVXLink Interfaces

I’ve been running the svxLink application written by Tobias, SM0SVX for some time now. I installed it on our local VHF repeater back in 2018 using a Raspberry Pi 3B+, and an audio/PTT isolation board. I’ve been looking for new, improved or simplified interfaces to interconnect svxLink with repeater controllers and simplex node radios. Some time ago, I purchased an RA-35 board from Masters Communications and recently put it to the test.

I purchased the kit version of the board. Surface mount components are already soldered onto the board and the rest is through-hole parts. It was a fun project to build.

Previously I’ve built all-in-one systems using Raspberry pi computers and interfaces in a custom designed 3D printed case. That makes for a fairly clean installation.

Another solution I have used is a Linux computer with an external interface such as the ELink Echolink Controller:

This solution uses either the internal sound card in the computer, or an external USB sound dongle for the RX and TX audio. As you can see, there are a lot of cables to connect between the computer and interface.

The RA-35 board is essentially a USB sound dongle (Cmedia CM-119A) with audio amplifiers (LM-386) for TX Audio. The board uses the CM-119A’s Mic input and provides a pot to adjust the RX audio input level. The CM-119A’s GPIO (general purpose input/output) signals are used to control PTT, COS, CTCSS, etc. The board also provides landings for connecting directly to other GPIO pins. Software on Linux interfaces to these signals through the hidraw facility. svxLink is able to interface to these GPIO ports directly through configuration options.

The RA-35 board also features a clever monostable (LM555) circuit that disables PTT/TX if the system or board fails and heartbeat goes away.

This makes for a very clean interface between any linux computer and a repeater controller or FM transceiver.

I initially tested this solution using an Alinco DR-135 VHF transceiver and I am very pleased with the results.

svxLink can be used to interconnect repeaters, links, and users over the Internet or it can be used to establish point to point links using its own protocols.

A reflector application written for use with svxLink nodes called “SVXReflector” can be used to provide functionality similar to Echolink reflectors.