Modes

Related wiki pages Repeater listings, APRS, D-Star, Echolink, 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:

<math>x(t) = (A + m(t))\cos( 2 \pi f_c t + \phi )</math>

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.

<math>x(t) = \cos( 2 \pi ( f_c + \Delta f m(t) t + \phi ) )</math>

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.

<math>x(t) = \cos( 2 \pi ( f_c t + \Delta \phi m(t) ) )</math>

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.

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.

Radio Teletype (RTTY)

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

Amplitude Shift keying (ASK)

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

See Wikipedia Amplitude Shift Keying 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.

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.

Common PSK frequencies

(subject to propagation characteristics.)

BAND	FREQ MHz
160M	1.838
80M	3.580
40M	7.035 DX
40M	7.070 US
30M	10.140 DX
30M	10.142 US
20M	14.070
17M	18.100
15M	21.070
15M	21.080
12M	24.920
10M	28.120
6M	50.290
2M	144.150
1.25M	222.070
70cm	432.200
33cm	909.000

See Wikipedia Phase Shift Keying Wikipedia: PSK31, Wikipedia: 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 Software page.

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