Modes

Related wiki pages Repeater listings, APRS, D-Star, Echolink, Emission Classification, IRLP, Packet, Slow-Scan Television (SSTV), Fast-Scan Television (ATV), Optical communications, WSPR, WSJT, Software, QRP

The term mode has varying meanings, according to the context, but the most common are permitted modes in amateur licensing.

Waves have three characteristics that can be changed, Amplitude, Frequency and Phase. A mode is the way of changing electromagnetic waves, modulating them so that transmission of information is possible. Modulating signals can be either analogue, for example sound or digital, for example simple binary on-off.

= Analogue Modulation methods =

There are two main analogue modes, or methods of modulation: Amplitude Modulation (AM), in which the phasor amplitude changes, and Angle Modulation, in which the phasor angle changes.

Double Sideband (DSB), Single Sideband (SSB) and Vestigal Sideband (VSB) are all forms of AM. Frequency Modulation (FM) and Phase Modulation (PM) are all forms of Angle modulation.

Amplitude Modulation (AM)
The transceiver produces a carrier wave at the frequency of transmission. Voice is superimposed on the carrier wave, and alters its shape by changing the Amplitude or height of the wave. Hence the frequency and wavelength of the carrier do not change with this form of modulation.

See Amplitude Modulation for more information.

Double-Sideband Modulation (DSB)
Double Sideband is what's usually meant when people talk about AM. In DSB transmissions, the message signal is transmitted in two sidebands, one being the mirror image of the other. The carrier may be either transmitted at full power (DSB-FC), at reduced power (DSB-RC), or completely eliminated (DSB-SC).

Conceptually, the power level at the carrier frequency, equates to the DC bias in the input signal. Mathematically, it looks something like this:

$$x(t) = (A + m(t))\cos( 2 \pi f_c t + \phi )$$

Single-Sideband Modulation (SSB)
Single sideband is what you get if you take a DSB-SC signal, and pass it through a sharp high-pass or low-pass filter to reject the offending sideband. It may be generated through high-pass/low-pass filter, or it may be done using a Harley Modulator, which cancels out the unwanted sideband through the use of a Hilbert Transform.

Frequency Modulation (FM)
The transceiver produces a carrier wave, in the same way as for Amplitude Modulation. In this case however, voice is added to the carrier so that is frequency changes. This in turn affects the wavelength of the carrier, but the amplitude remains constant.

See Wikipedia's Frequency Modulation article for more information.

$$x(t) = \cos( 2 \pi ( f_c + \Delta f m(t) t + \phi ) )$$

Phase Modulation (PM)
This mode is seldom used in amateur radio. It's very similar to FM, but rather than the frequency changing, it's the phase of the signal that changes according to the modulating signal.

$$x(t) = \cos( 2 \pi ( f_c t + \Delta \phi m(t) ) )$$

The well-known PSK31 digital mode is a form of phase modulation.

Lesser known modes

 * Quadrature amplitude modulation (QAM). In this mode, two carrier waves, 90° out of phase with each other are produced. QAM is a variant of AM, in which both carriers are modulated by an audio signal.

= Digital modulation =

Technically, whenever a signal is turned on and off to enable transmission of information, it can be considered to be a digital mode. Under this definition, CW is certainly a digital mode. This section refers to methods of transmitting and receiving (rather than modulating) that are digital, or that require digital processing in part of the transmission or receiving process.

Wiki page for digital mode software

Amplitude Shift keying (ASK)
Also known as Off/On Keying, (OOK)

Amplitude-shift keying (ASK) is a form of modulation in which digital data is sent as variations in the amplitude of a carrier wave. In this mode there are two states, carrier on and carrier off, hence the name off/on keying.

ASK is sensitive to atmospheric noise, distortions and propagation conditions. Because light can be controlled to have two states, on and off, ASK is also commonly used to transmit digital data over optical fiber.

See Wikipedia Amplitude Shift Keying for more information.

Continuous Wave (CW)
Related wiki page: What is the best way to learn Morse?, Morse Code

A continuous wave is an electromagnetic wave of constant amplitude and frequency, a pure carrier, and information is carried by turning the wave on and off, and measuring the interval. Morse code is often transmitted using CW.

See Wikipedia Continuous Wave for more information.

Frequency Shift Keying (FSK)
The frequency of the carrier is varied according to a digital signal.

See Wikipedia Frequency Shift Keying for more information.

MFSK - Multiple Frequency Shift Keying
In MFSK data is sent using many different tones. MFSK is used by several digital modes including MFSK16, Throb, Olivia and Ale and Domino. The advantages of MFSK compared to other FSK modes are:
 * good noise rejection
 * low propagation distortion
 * less effects from multi-pathing
 * low error rates

Some limitations of MFSK are:
 * high stability transceivers are required for effective transmission and reception. Exception: Olivia and Domino which are very drift tolerant.
 * some interference effects from ionospheric multipathing
 * some interference from constant carrier signals

External Links to MFSK sites:


 * General information about MFSK


 * ALE Automatic Link establishment. Information and downloads.


 * Domino EX has plenty of info and download links.


 * Olivia includes information, download links and frequencies used.


 * Throb screenshot and download link.

AMTOR
Also known as SITOR in its commercial form.

AMTOR comes in two types, Type A and Type B.

Type A: information is repeated if requested by the receiving station.

Type B: All information is transmitted twice

Also known as SITOR in its commercial form.

AMTOR comes in two types, Type A and Type B.

Type A: information is repeated if requested by the receiving station.

Type B: All information is transmitted twice

The frequency of the carrier is varied according to a digital signal.

Wikipedia article

CLOVER
CLOVER is a PSK mode which provides a full duplex. There are two CLOVER variants, CLOVER I and CLOVER II. Perhaps the most interesting characteristics of Clover is that it adapts to conditions by constantly monitoring the received signal and changes modulation scheme in response.

Wikipedia clover article

G-TOR
Invented by M Golay, G-TOR (Golay-TOR) was used to transmit the early Jupter and saturn space mission pictures back to earth. Is an FSK mode that has faster transfer rate than Pactor. To minimize the effects of atmospheric noise, a data interleaving process is employed. This has the added advantage that garbled data can be decoded. GTOR is a proprietary mode developed by Kantronics and is rarely used by radio amateurs.

PACTOR
Designed by Peter, DL6MAA and Ulrich, DF4KV asa an alternative to both AMTOR and packet. It has three incarnations, PACTOR I, PACTOR II and PACTOR III. These are effective under weak signaql and high noise conditions. PACTOR is not commonly sed by amateurs.

Wikipedia PACTOR article

Radio Teletype (RTTY)
RTTY or "Radio Teletype" is an FSK mode that has been in use longer than any other digital mode except for morse code. RTTY is a very simple technique which uses a five-bit code to represent all the letters of the alphabet, the numbers, some punctuation and some control characters.Transmissions are at approximately 60 wpm (words per miute). Because there is no error correction provided in RTTY, noise and interference can have a serious impact on transmissions. RTTY is still popular with many radio amateurs.

RTTY frequencies
As a general general rule of thumb RTTY is usually found between 80kHz and 100kHz up from the lower edge of each band, except for 160M and 80M.


 * 160M - 1800 to 1820 (RTTY is rare on this band)
 * 80M - 3580 to 3650
 * 40M - 7080 to 7100 (differs from region to region)*
 * 30M - 10110 to 10150
 * 20M - 14080 to 14099
 * 17M - 18095 to 18109
 * 15M - 21080 to 21100
 * 12m - 24915 to 24929
 * 10M - 28080 to 28100
 * 6m - 50300 AFSK and 50600 = FSK

A listing of RTTY frequencies used for weather, ham radio bulletins and for other purposes can be found here

Packet
Data is transferred form transceiver to receiver in packets or groups of data bits. This mode was popular in the late 1970's and early 1980's, but has decreased in use since then.

Wikipedia packet article

Phase Shift Keying (PSK)
The phase of the carrier is modulated by a digital signal. In its simplest terms, this could mean for example that the phase of the carrier is turned through 180° with each change in the digital signal. In practical terms, PSK allows long distance communication even when noise level are high.

Wikipedia PSK article

Wikipedia PSK31 article

Common PSK frequencies
(subject to propagation characteristics.)

See Wikipedia Phase Shift Keying PSK31, PSK63, "NUE-PSK Digital Modem".

Digital modes in practice
The licensing regime defines digital modes as those modulation techniques that require digital data processing. In Australia refer to the ACMA LCD ( Licence Conditions Determination) for exact details. You will need to scroll down the page to find the link.

To get on air in digital modes normally an SSB transceiver is used which is coupled to a computer via a so called interface.

As a minimum the interface requires 4 signals from the transceiver:
 * 1) Audio in - where you would connect the microphone for SSB.
 * 2) Audio out - for the loudspeaker.
 * 3) PTT.
 * 4) Ground.

On the computer side you need corresponding signals from the computers sound-card or integrated sound system:
 * 1) Audio out - the audio generated by a digital modes program on transmit.
 * 2) Audio in - either the "microphone-in" or the "line-in" connector of the sound-card.
 * 3) PTT - often the RTS or DTR signal of a serial port is used for this. PTT can also be generated within the "interface" by a VOX like circuit.
 * 4) Ground.

The computer has to run a digital modes program - see the digimodes software page.

What do digital modes sound like? Click here to find out.