Glossary – Transmission

An aerial has the same function as an antenna but is a more general term usually applied nowadays to larger or flexible wire structures.

Alternative Frequency. The list(s) of alternative frequencies give information on the various transmitters broadcasting the same programme in the same or adjacent reception areas, and enable receivers equipped with a memory to store the list(s), to reduce the time for switching to another transmitter..

An antenna is a small rigid  metallic structure designed to convert radio frequency energy to electromagnetic waves which are launched into free space – or equally to convert radio waves received into radio frequency energy.

Electronic equipment that increases strength of signals passing through it

To reduce the intensity of a signal.

A waveform suitable for modulation by an information bearing signal.

Clock Time and Date. The listener, will not use this information directly and the conversion to local time and date will be made in the receiver’s circuitry. CT is used as time stamp by various RDS applications – such as setting a recievers (or car) time and date.

Used to compress an audio signal so that it conforms within desired parameters.

Electromagnetic spectrum:
The complete range of stored or propagating electric and magnetic field energies.  The lower part of the spectrum is known as non-ionising energy and includes power line frequencies, radio frequencies, infrared, visible light and ultra violet.  The upper part of the spectrum is known as ionising energy and includes x-rays and gamma rays.

EMF or electromagnetic fields or electromagnetic waves:
Emitted by many natural and man-made sources.  Used to transmit and receive signals.

Enhanced Other Networks. This feature can be used to update the information stored in a receiver about programme services other than the one received. Alternative frequencies, the PS name, Traffic Programme and Traffic Announcement identification as well as Programme Type and Programme Item Number information can be transmitted for each other service. The relation to the corresponding programme is established by means of the relevant Programme Identification. Linkage information, consisting of four data elements, provides the means by which several programme services may be treated by the receiver as a single service during times a common programme is carried. Linkage information also provides a mechanism to signal an extended set of related services.

The low-power RF stages of a radio transmitter.

Feeder Cable:
A coaxial cable which feeds a transmission antenna with energy from a transmitter – or feeds a receiver with a signal from free space.

Field strength:
The amplitude of the electric or magnetic fields.  Related to power density through the impedance of free space.

Free Space:
The Earth’s atmosphere in addition to what is conventionally termed “space”

The number of times per second at which an electromagnetic wave oscillates.  Determines the wave’s properties and usage.

Hz (KHz / MHz / GHz):
The hertz (symbol: Hz) is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of sinusoidal waves, particularly those used in radio and audio applications.

A device to limit an audio signal if the volume level is too high. Large volume levels can either damage sensitive equipment or can sound distorted when listened to on air.

M/S (RDS):
Music/Speech switch.This is a two-state signal to provide information on whether music or speech is being broadcast. The signal would permit receivers to be equipped with two separate volume controls, one for music and one for speech, so that the listener could adjust the balance between them to suit his individual listening habits.

Modulation is the process of varying one or more properties of a high-frequency periodic waveform, The three key parameters of a periodic waveform are its amplitude, its phase and its frequency, all of which can be modified in accordance with a low frequency signal to obtain the modulated signal.

Overmodulation is when the instantaneous level of the modulating signal exceeds the value necessary to produce 100% modulation of the carrier. In layman’s terms, the signal is going “off the scale”.

Mixed Polarity:
A method of propagation of electromagnetic waves where the energy is launched in more than one plane – often erroneously referred to as “combined” or “circular” polarity.

Programme Identification Code – Issued by Ofcom and programmed into your RDS encoder. This information consists of a code enabling the receiver to distinguish between countries, areas in which the same programme is transmitted, and the identification of the programme itself. One important application of this information would be to enable the receiver to search automatically for an alternative frequency in case of bad reception of the programme to which the receiver is tuned; the criteria for the change-over to the new frequency would be the presence of a better signal having the same Programme Identification code.

The way the radiated energy vibrates and hence the way the receiving antenna should be placed to react to it – usually either in a vertical or a horizontal plane.

Audio signal processing, is the intentional alteration of auditory signals, or sound. Audio Processing aids to prevent overmodulation, and minimize it when it occurs, adjust overall loudness to desired level and correct errors in audio levels.

The method of launching radio waves into free space

Propagation Plot:
An image produced by computer simulation to illustrate how a transmitter will serve a given area

Programme Service. This is the label of the station service consisting of not more than eight alphanumeric characters which is displayed by RDS receivers in order to inform the listener what service is being broadcast “_BBC_R2_”.

Programme Type: This is an identification number to be transmitted with each programme item and which is intended to specify the current Programme Type within 31 possibilities. This code could be used for search tuning. The code will, moreover, enable suitable receivers and recorders to be pre-set to respond only to programme items of the desired type.

RadioText: This refers to text transmissions primarily addressed to receivers, which would be equipped with suitable display facilities. Scrolling Information available to

Radio Data System, an information system which allows broadcasters to supply information to a reciever.

Radio Frequency.

Radio Text. Scrolling Information supplied to the reciever.

Traffic announcement identification: This is an on/off switching signal to indicate when a traffic announcement is on air. The signal could be used in receivers to:

  1. switch automatically from any audio mode to the traffic announcement;
  2. switch on the traffic announcement automatically when the receiver is in a waiting reception mode and the audio signal is muted;
  3. switch from a programme to another one carrying a traffic announcement, according to possibilities available through EON.

After the end of the traffic announcement the initial operating mode will be restored

Traffic Programme identification: This is a flag to indicate that the tuned programme carries traffic announcements. The TP flag must only be set on programmes which dynamically switch on the TA identification during traffic announcements. The signal shall be taken into account during automatic search tuning.

Abbreviation for ultra high frequency.

Very High Frequency – the correct term for 30 to 300 MHz, the section of the frequency spectrum occupied by FM signals in Band II – 87,5 to 108,0 MHz. Other spectrum sections in use for broadcasting are termed LF, MF, HF, UHF, SHF and EHF.

Yagi Antenna:
A multiple-element directional antenna format. This list is by no means comprehensive and we would be delighted to explain any other terms you may find confusing.