Charles Martin Reid - Radio/Digital Modes

From charlesreid1

Radio modem for a microcontroller: PSK31, RTTY, APRS:

HF voice: speech codec for 3200 bps and lower:

  • comes with FDMDV modem, PSK modem, and api for embedding in other programs


In ham radio, digital modes are ways of communicating digital information using radios. Normally, with analog communications, the operator and/or receiver radios will be operated by a human. The information being transmitted is human voice data, or some other information a human can understand (CW). With digital modes, the data being transferred is digital data, and the transmitting and receiving radios are operated by computers. These computers are able to translate analog signals to digital signals, or vice versa, using a modem (a modem modulates and demodulates signals).

Exploring digital modes can be done with a Linux or Windows computer, or with a phone. A radio helps, but is not necessary to get your feet wet.

The setup consists of two parts. The first part is a computer or phone: this turns digital information into analog signals that can be sent out over the radio (via the device's soundcard). The second part is a radio, which receives the analog signal from the computer and transmits it, or receives an analog signal and sends it to the audio input of the digital mode program.

|   Computer            |
| (digital data         |
|  2 analog signal)     |
|   Radio Transceiver   |       \|/
| (analog radio signals |        |
|   2 audio in/out)     |________|

The List

Listed below are a few different digital modes, how they work, and what software to use.

Digital modes:

  • SSTV
  • PSK31/PSK63
  • MFSK
  • Olivia
  • RTTY
  • APRS
  • D-Star
  • GSM
  • GPRS
  • TCP/IP over Packet

Slow Scan TV (soundcard to soundcard)

Main page: SSTV

Slow scan TV turns images into audio signals that can be transmitted over long ranges. Software can translate images into sounds, and sounds into images. QSOs are made by exchanging a series of images.

To do SSTV on the computer, use Qsstv.

To do SSTV on Android, use Robot36.

Here's an example of testing out an SSTV transmit and receive functionality without radios involved:

Slow Scan TV with Android from charlesreid1 on Vimeo.

PSK (soundcard to soundcard)

Main page: PSK (phase-shift keying)

PSK31 and PSK63 are a method of translating digital ASCII text into sound waves, which can then be transmitted and received by radios. Like SSTV, you don't need radios to test out communication between two nodes with this mode, you just need two computers, or a computer and a phone.

On the computer, you can transmit/receive PSK signals using Fldigi. (Fldigi is a program with a huge range of digital modes available for you to use to transmit/receive.)

On an Android, you can transmit/receive PSK signals using apps. DroidPSK works reasonably well, but is limited to PSK31 or PSK63.

PSK in action:

PSK31: Fldigi to DroidPSK from charlesreid1 on Vimeo.