Computer and Radio interfacing - chaos

 The mess that is computer control of your rig. 

Connections!

On our computers we have almost universally today just USB input/outputs. These can handle digital audio input/output and/or serial data communications. Often two USB A connection are used for audio and serial separately, on others a single USB C handles both audio and serial. And this works, with the coveat that some OSs demand careful driver and levels setups. I am using a MacBook Air and frankly it just works, no driver installations, no fiddling around with sound panels!

Interface computer and radio

We need to send audio in and get it out, which needs an A to D and D to A convertors, running at any of the standard PCM audio bit rates from 8kHz to 192kHz! 48kHz is common.

The biggest issue is the serial data control data from and to our transceivers. There are two main camps, one using sequences of hexadecimal numbers (ICOM, Yaesu not the same), the other using much simpler ASCII character strings (Kenwood). Add to this the signal for PTT, which can be a special sequence of serial CAT signals, or a hardware serial interface RTS or DTR lines, of the right polarity.

And to interface the computer USB serial data to separate TX and RX digital lines, which can be 5V or 3V3 volt levels and speeds of anywhere from 9600 to 38400 baud (possibly lower or higher), the logic must be correct for example positive logic where +5V = logic ‘1’ and 0V = logic ‘0’, or it could be negative logic with +5V = logic ‘0’ and 0V = logic ‘1’. The serial data must also have the correct format, for example one start bit, 8 data bits and one stop bit, a total of 10 binary bits.

For ICOM radios, to make things worse, these signals are carried on a single wire C-IV, not two separate connections TX & RX, requiring special I/O circuitry between the computer and the radio.

Then comes the problem of the rig audio levels. What does it need for input and output? These could be standard line levels (about 1V rms) or most likely the direct Microphone (10-100mV) and LS output (0-5V). With various input impedances of maybe 100R to 10k and rig output impedance suitable for driving an 8R loudspeaker.

Finally some radios have moved completely away from audio and data interfaces to use WLAN and communicate with your computer over LAN and via your home router. Giving the advantage of remote operation. But here again we have a new set of communication protocols and signalling.

Xieigu G1M example

A couple of blog posts back I describe the fiddling around I had to do to get my Xiegu G1M to work FT8

Better solution in the ELAD FDM-DUO

On the other hand my FDM-DUO is simplicity itself. It has separte USB B connectors for CAT and TX/RX digital audio (standard printer cables can be used). These can be connected through a simple 2 x USB A to USB C Hub to my MacBook Air where they appear as a digital "device" and an audio "device" which can be selected directly in WSJT-X. Which also has a built-in "hamlib" control configuration for the FDM-DUO. And it all just works. 

QRP Labs is the best

Even better solution from QRP Labs on their Digital Transceiver QDX. A single USB connection carrying both the CAT serial data and the digital audio from a built-in "sound card". One wire, just plug it in. Excellent.

Follow me

The rest of the radio industry needs to follow ELAD and QRP Labs QDX and provide a simple USB connection direct to our computers, with implemented CAT signalling - preferably using ASCII text commands.