Modes

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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.

Contents

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 on Wikipedia 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 Frequency Modulation on Wikipedia 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.

In analogue radio, phase modulation differs only vary slightly from frequency modulation as mathematically frequency is the rate of change of phase. In FM, output frequency deviation is directly proportional to input signal amplitude only. A PM signal looks much like an FM signal except that output frequency deviation is directly proportional to both input signal amplitude and input frequency. An FM receiver would therefore receive a PM signal, but high frequencies in the audio would be pre-emphasised by 3dB/octave.

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 each of these two carriers is modulated by a separate audio signal. QAM or a variant thereof had been used in many AM Stereo broadcast radio systems as well as for the colour subcarrier on analogue fast-scan TV transmissions.

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.

QRSS - Slow Morse

The term QRSS comes from the Morse Code Q-Code QRS which means either "Shall I send more slowly?" or "Please send more slowly"

In practice QRSS has a dot time-length of 3 seconds or more, and occupies a very narrow bandwidth - as low as 1Hz.

QRSS signals are monitored by "grabbers" such as those listed on this site from I2NDT.

Grabber software can be obtained from theQRSS VD site, and instructions on how to set up a grabber site can be obtained here.

This clipboard has probably the most up to date information about qrss beacons and grabbers.

Kits can be obtained here.

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:

  • ALE Automatic Link establishment. Information and downloads.
  • Domino EX has plenty of info and download links.
  • Olivia includes information, download links and frequencies used.
  • ROS digital Download the latest version and contribute to the blog.
  • Throb screenshot and download link.

AMTOR

Amateur Teleprinting Over Radio

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. This is known as ARG (Automatic ReQuest)

Type B: AMTOR B uses FEC (Forward Error Correction)to ensure data is transmitted with as little loss as possible. This is accomplished by sending each character twice, with three seconds between each end.

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

Wikipedia article [1]

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. Some features:

  • a 16 bit CRC (Cyclic Redundancy Check). This process involves the transmitting station sending a checksum with the data. The receiving station compares the checksum with the recieved data, andf can request either new data, a resend of data or a change of baud rate.
  • Baud rates of 100, 200 or 300 to suit varying conditions.

PACTOR

PACTOR is a hybrid of Packet and AMTOR

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.

In its original form, RTTY was a very simple technique which used a five-bit Baudot code to represent all the letters of the alphabet, the numbers, some punctuation and some control characters. Transmissions were at approximately 60 wpm (words per minute). More recent implementations operate at higher bitrates using the same ASCII code used for standard computer data.

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 from transceiver to receiver in packets or groups of data bits. Typically, this involves connection of transceiver audio to a terminal node controller, which handles demodulated modem signals and provides some level of automated error correction. APRS (automated packet reporting system, automated position reporting system) is one example of a packet radio system; it is commonly used to provide weather beacons and GPS tracking for unmanned craft such as weather balloons.

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

PSK reporter reports who has been seen using psk.

Common PSK frequencies

(subject to propagation characteristics.)

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



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 digimodes software page.

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

VOIP (Voice Over IP) Modes

VOIP is not considered by some hams as being a "true" ham mode. These modes are reliant to some extent on using the internet to transfer voice from one station to another. For example, IRLP users transmit from radio into a "node" - their voice is transferred via the internet to another node, from where it is transmitted from another radio to the receiving station. The link between radios is therefore via the internet.

One advantage of these modes is that hams in restricted communities can have contacts with hams in far distant lands with basic equipment.

Some VOIP modes, for example CQ100 do not require a radio at all as the "rig" is software created and driven.

All VOIP modes require some ham radio certification

See also

External links


Modes of operation
Modes CW * AM * FM * SSB * Digital * Echolink * Emission Classification * IRLP * Optical communications
Packet APRS * D-Star
SSTV and ATV SSTV frequencies * SSTV Modes
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