1. Beginners’ Questions Answered

1.1. What is Fldigi?

Fldigi is a computer program intended for Amateur Radio Digital Modes operation using a PC (Personal Computer). Fldigi operates (as does most similar software) in conjunction with a conventional HF SSB radio transceiver, and uses the PC sound card as the main means of input from the radio, and output to the radio. These are audio-frequency signals. The software also controls the radio by means of another connection, typically a serial port.

Fldigi is multi-mode, which means that it is able to operate many popular digital modes without switching programs, so you only have one program to learn. Fldigi includes all the popular modes, such as DominoEX, MFSK16, PSK31, and RTTY.

Unusually, Fldigi is available for multiple computer operating systems; FreeBSD™; Linux™, OS X™ and Windows™.

1.2. What is a Digital Mode?

Digital Modes are a means of operating Amateur radio from the computer keyboard. The computer acts as modem (modulator - demodulator), as well as allowing you to type, and see what the other person types. It also controls the transmitter, changes modes as required, and provides various convenient features such as easy tuning of signals and prearranged messages.

In this context, we are talking about modes used on the HF (high frequency) bands, specifically chat modes, those used to have a regular conversation in a similar way to voice or Morse, where one operator talks for a minute or two, then another does the same. These chat modes allow multiple operators to take part in a net.

Because of sophisticated digital signal processing which takes place inside the computer, digital modes can offer performance that cannot be achieved using voice (and in some cases even Morse), through reduced bandwidth, improved signal-to-noise performance and reduced transmitter power requirement. Some modes also offer built-in automatic error correction.

Digital Mode operating procedure is not unlike Morse operation, and many of the same abbreviations are used. Software such as Fldigi makes this very simple as most of the procedural business is set up for you using the Function Keys at the top of the keyboard. These are easy to learn.

1.3. Why all the different modes?

HF propagation is very dependent on the ionosphere, which reflects the signals back to earth. There are strong interactions between different signals arriving from different paths. Experience has shown that particular modulation systems, speeds and bandwidths suit different operating conditions.

Other factors such as available band space, operating speed and convenience, noise level, signal level and available power also affect the choice of mode. While in many cases several different modes might be suitable, having a choice adds to the operating pleasure. It is difficult to advise which mode is best for each particular occasion, and experience plays an important role.
[To gain a good insight into each mode and its capabilities, you might consider purchasing Digital Modes for All Occasions (ISBN 1-872309-82-8) by Murray Greenman ZL1BPU, published by the RSGB and also available from FUNKAMATEUR and CQ Communications; or the ARRL’s HF Digital Handbook (ISBN 0-87259-103-4) by Steve Ford, WB8IMY.]