Digital Audio Mixer Phase I

Modulation and a excellent antennas are the best tools for successful amateur-radio stations. That’s what I learned decades ago in the 11m band. With my new shack I spend sleepless nights to get the audio manipulated by mixing software in the PC. At the end I decided to use the audio on the PC for remote access, Skype, digimodes and future enhancements. To achieve this I looked deeper into studio equipment and from my history as radio and television technician I knew what I wanted. Doing some research and compared my outdated knowledge with what is possible today, I decided for the following setup:


Of course this needs a lot – and I mean A LOT of setup and testing until everything is connected correctly, but it is really great fun and very satisfying when every runs as planned. Also not to underestimate is the setting of the radios as I am here not operating with Mic-Level Input to the radio via the microphone connector, I am using Line-In Level through the DATA (ACC Connector at ICOM, DATA Connector at Yaesu) connectors on the backside of the radios. Icom and Yaesu do not say that they have Line-In Inputs, as they call it differently as you can see from this table.

Connection at Radio YAESU FT-857 / 897
DATA Connector Pin’s
ICOM IC-7300
ACC Connector Pin’s
To XLR Connector Pin male (Input to Mixer) To XLR Connector Pin female (AUX from Mixer)
Microphone in (Line-Level) Pin 1 DATA In (TXA) Pin 11 MOD   Pin 2
Audio Out (Line-Level) Pin 5 DATA Out 1200 (RXA) Pin 12 AF/IF Pin 2  
PTT Pin 3 PTT (Transmit when connected to ground) Pin 3 SEND (Transmit when connected to ground) see note see note
Ground Pin 2 GND Pin 2 GND Pin 1 and Pin 2 (shortened) Pin 1 and Pin 2 (shortened)

Note: For PTT you may want to have a hand-or foot switch. For this, please connect a 6.3mm female mono plug with cable to the PTT and Ground connectors of each radio. Than you can use a Hand- or Foot-Switch with a 6.3 mm mono male plug to connect your switch ! If you want to use it together with the “total remote shack” idea, you need applications which allows you to go on transmit with a click of the mouse.


ICOM ACC Socket (seen from the rear side of the male connector) YAESU FT-857 / 897 DATA Socket (seen from the rear side of the male connector)

Signal-path wise here is a rule of thumb. For each application on the PC which has either audio out or audio in or both, I use a USB Audio Adapter together with the USB Audio Isolator to avoid noise from the PC on the mixer, if you want to use the PC’s or Laptop build in Audio Connectors you will need a DI-Box which cost from 10€ onwards, But think twice before you buy, you need a DI-Box for each connection, that means if you want to connect stereo in to the computer = 2x DI-box, for stereo out, 2x DI-Box. It is sometimes easier, cheaper and space-saving to buy 19″ Rackmount units for 108€ with 8 DI-Boxes inside one box like this one which you can easily stack if needed. The Radio’s are connected to Audio in (Speaker) or Audio out (Microphone) with Line-Level and adapter cables to the mixer (it’s called IN and AUX). In terms of controlling the radios and sending signals for digimodes the radios are connected to the PC and the necessary applications. This does not conflict, as you can switch Signals with the mute button on the mixers control panel things on and off and you can create snapshots on the mixer for different settings. As I am currently not into digimodes, this has not been tested throughout but should do from the blueprint.

Creating the right Windows PC

Since 4+ years a multi-media PC with a small form factor, quite powerful and with a lot of interfaces (WLAN, LAN, 4 USB-2, 2 USB-3, surround sound, mic, speakers, optical and coax digital in- and outputs, hdmi, vga and dvi) was standing unused in the living room and was now selected as the perfect victim for my new amateur radio activity. with 4GByte of RAM definitely too low on storage but the harddisk with 500GByte ATA Interface big and fast enough. Upgraded the memory to 16GByte, bought a Windows 7 professional license (Windows 10 is too much for my taste) and installed the base system. After 4 days all 300+ windows patches were downloaded and together with about 50 restarts installed.

OK,  the thing was finally up !

As the first radio which I bought was a Yaesu FT-857D, I got the CAT-Serial to USB Interface-Cable and the SignaLink USB Modem installed as prescribed in the manuals and it worked together with the applications nearly everyone uses, from FlDigi, FlRig to HRD and so on, like a charm. Unfortunately the SignaLink has it’s own VOX PTT, which makes it difficult to use the SignaLink as a modem for voice from the computer to the radio. If you run your microphone signals through sound processing software in the PC, every noise around you triggers the VOX PTT in the SignaLink and makes the Radio transmit.

For sure I am not telling you new stuff here, but my aim was to have a complete remotely controlled setup in my shack which I can use from anywhere in the world without modifying my router, creating DYNdns entries, piercing the firewall (opening incoming ports) of the DSL-Router, just to have one or two applications remotely available. I wanted the whole PC and all radios everywhere and on other computers (independent of operating system), mobile devices (Android and iOS) and for experiments also on a Raspberry Pi 3+ or higher.

Furthermore I wanted when in the shack a complete wireless setup, that I do not have to be glued to the chair in front of the radios, including wireless PTT.

How to do this I explain in the following posts.