What are Digital modes
Digital modes require a interface between a Computer and a Transceiver. On most of the newer models of Transceivers they have a Sound Card interface built in which means the Transceiver connects to the Computer via a USB cable. If you have a Transceiver without a built in Sound Card, you will need to buy one or if you like “Homebrewing” make one yourself.
There are various digital modes that are used in amateur radio. I will start of with the newest modes first.
FT8 — This is a mode that was released to the amateur community in June 2017. It was developed by K9AN and K1JT. The mode name “FT8” stands for “Franke and Taylor, 8-FSK modulation”. FT8 uses 15-second T/R sequences and provides 50% or better decoding probability down to -20 dB on an AWGN channel. An auto-sequencing facility includes an option to respond automatically to the first decoded reply to your CQ. FT8 QSOs are 4 times faster than those made with JT65 or JT9. FT8 is an excellent mode for HF
DXing and for situations like multi-hop E_s on 6 meters, where deep
QSB may make fast and reliable completion of QSOs desirable.
JT65 — developed and released in late 2003, is intended for extremely weak but slowly varying signals, such as those found on troposcatter or Earth-Moon-Earth (EME, or “moonbounce”) paths. It can decode signals many decibels below the noise floor in a 2500 Hz band (note that SNR in a 2500 Hz band is approximately 28 dB lower than SNR in a 4 Hz band, which is closer to the channel bandwidth of an individual JT65 tone), and can often allow amateurs to successfully exchange contact information without signals being audible to the human ear. Like the other modes, multiple-frequency shift keying is employed; Operators have also begun using the JT65 mode for contacts on the HF bands, often using QRP (very low transmit power)
JT9 — intended for MF and HF use, was introduced in an experimental version of WSJT, known as WSJT-X. It uses the same logical encoding as JT65, but modulates to a 9-FSK signal. With 1-minute transmission intervals, JT9 occupies less than 16 Hz bandwidth. JT9 also has versions designed for longer transmission intervals of 2 minutes, 5 minutes, 10 minutes or 30 minutes. These extended versions take increasingly less bandwidth and permit reception of even weaker signals.
RTTY — uses a form of transmission known as frequency shift keying. The code representing the letters consists of a series of bits represented by high and low voltages. In turn these are represented on the radio signal by a shift between two frequencies, one frequency signifying a mark or high voltage and another frequency representing a space of a low voltage. The carrier for the RTTY signal is shifted between two frequencies, and this gives rise to differing audio tones when a beat frequency oscillator or BFO is used. The code for the data to be sent consists of five bits of either a mark or a space for each character. The actual code that is used is called Baudot. 45.5 baud is the standard speed for amateur radio HF operation.
PSK31, 63, 125 — is widely used, particularly on the HF amateur radio bands where its up to date features enable it to offer advantages over modes such as RTTY. It incorporates error correction techniques along with the use of a full ASCII and ANSI character set which enables it to fit in with modern day computer and telecommunications technology. PSK uses a form of modulation known as phase shift keying (PSK). This is rather different to the frequency shift keying that is used for modes such as RTTY. PSK involves reversing the polarity, or phase, of the signal (180 deg. phase shifts), and has been likened to reversing or swapping over the two wires in an antenna connection. However, in reality the phase reversals are not achieved in this way; instead they are generated and detected in the audio sections of the SSB transceiver being used. There are various forms of PSK and the form of PSK described is actually known as binary phase shift keying (BPSK) and it is more efficient than either frequency shift keying, which has a greater bandwidth, or on/off keying which does not use the power as efficiently. PSK31 uses a novel form of data encoding. When sending asynchronous ASCII data, systems use a fixed number of data bits as well as start and stop bits. It is possible to add error correction to the system. However, to achieve this it is necessary to use a form of keying called quadrature phase shift keying (QPSK). Instead of two phase states 180 deg. from one another, QPSK uses four phase states, each 90 deg. from one another. However, in operation on the bands it has been found that error correction with the use of QPSK only sometimes gives mprovements over ordinary BPSK.
Olivia MFSK — -is an amateur radioteletype protocol, using multiple frequency-shift keying (MFSK) and designed to work in difficult (low signal-to-noise ratio plus multipath propagation) conditions on shortwave bands. The signal can still be properly copied when it is buried 10 dB below the noise floor (i.e. when the amplitude of the noise is just over 3 times that of the signal). It is commonly used by amateur radio operators to reliably transmit ASCII characters over noisy channels using the high frequency (3–30 MHz) spectrum. Olivia modes are commonly referred to as Olivia X / Y (or, alternatively, Olivia Y / X ), where X refers to the number of different audio tones transmitted and Y refers to the bandwidth in hertz over which these signals are spread. Examples of common Olivia modes are 16/500, 32/1000 and 8/250.
