Technical parameters for broadcast radio transmitters

Published: 21 July 2023
Last updated: 17 May 2024

The following information comprises details of the technical parameters of all analogue VHF, MF, and DAB transmitters (including services on multiplexes) currently on-air.

In-use parameters are included mainly for listeners and aerial installers who may wish to know more about the nature of the signals they are receiving and possibly optimise their aerial accordingly. The maximum allowed parameters (within the terms of each licence) for analogue services are also included for the benefit of those, principally in the industry, who wish to make calculations, particularly about interference, for coverage-planning purposes. The format is intended more for ease of download and transfer into specialist databases, than for presentation.

Additionally, CSV data is provided for viewers who don’t use MS Excel or a compatible application.

The TxParams data will be refreshed regularly as new transmitters are added, modified, or suppressed.

This update contains some additional records for recently commissioned transmitting stations.

Last updated 17 May 2024

Date: Is the date on which the new (or modified) transmitter started radiating, which for a new service would normally precede the official launch date by a few weeks. Where no date is given, the station will have come on-air before January 1991 and have remained unchanged since then.

Station: Is the callsign. Don't be surprised if it changes mid-licence, and it may refer to a band rather than an actual frequency. (e.g. Music107 might actually be on 107.4 MHz.)

Area: Is a general indicator, and in the case of some smaller relays, might on occasions be described by the wider station coverage.

Site: Is the name of the site. Whilst we try to unify these, names can still vary across different organisations. Alternatively, sites will often carry more than one frequency/transmitter and could describe a number of masts in the immediate vicinity.

Frequency: Will either be in MHz for VHF stations or kHz for MF stations.

OS National Grid Reference (NGR): Gives the location of the transmitter, and normally refers to the bottom left-hand corner of the 100m square within which the mast lies.

Site height: gives the height of the base of the mast/building (in metres), above sea level.

Aerial height: Is the height of the transmitting aerial above ground level. For VHF aerials this will often be part-way up a mast, but for MF stations it normally refers to the whole length of the mast.

In-use ERP/HP or in-use ERP/VP: For VHF transmitters, this shows the effective radiated power (ERP), ie the power that would be radiated from a suitable polarised half-wave dipole when connected to a power source of this amount, in either the horizontal (HP) or vertical (VP) plane of polarisation. These reflect the maximum levels achieved in azimuth around the points of the compass, and are normally, but not always, on the same bearing in each polarisation.

In-use EMRP: For MF transmitters, this is the maximum effective (monopole) radiated power.

Maximum direction: Gives an approximate direction where an aerial radiates significantly more on any particular bearing. It takes reasonable account of differences between polarisations (see above) and multiple lobes.

In-use radiation patterns: Show the reductions in dB, in 10° steps in azimuth, starting with 0 and ending with 350, for each polarisation plane in the case of VHF (normalised to the In-use ERP/HP or In-Use ERP/VP respectively). Only one set of reductions is included for MF transmitter, normalised to the In-use EMRP.

Licensed ERP/HP and ERP/VP: In-use levels cannot exceed these licensed ones.

Licensed EMRP: In-use levels cannot exceed these licensed ones.

Licensed horizontal radiation patterns: In-use levels cannot exceed these licensed ones.

RDS: This data applies to VHF stations.

Programme service (PS) name: Is what should appear on an RDS radio when tuned to the station concerned. These are not rigidly controlled and obviously change when a station name changes. We do not wish to be advised of anomalies.

PI code: This is a geographically unique code that is hidden in the RDS datastream. It is an important factor in the way that an RDS radio switches between alternative frequencies, but you need to be well acquainted with your RDS instruction manual before assuming that the information here is incorrect! The PI Code will sometimes be used to cross-refer to the same service on DAB (SId).

Switched: This is a secondary PI code (see above) which is used if a transmitter in a supra-regional network uses a local opt-out. The switched code is broadcast as an alternative to the main PI code while the transmitter is broadcasting local content.

TP/TA: A ‘Y' indicates that, not only does this station produce traffic information, but it has dynamic control of its TA flag. This will do certain things when a station in the area has traffic information to convey (like turn up the volume or even switch on the radio) but it won't tune you automatically to another commercial station. It could, however, switch you to a DAB service, or vice versa.

Traffic message channel (TMC) for delivering traffic and travel information to drivers. It allows silent delivery of high-quality, accurate, timely and relevant information, without interrupting normal services. When data is integrated directly into a navigation system, this gives the driver the option to take alternative routes to avoid traffic incidents.

This is not to be confused with TP/TA which applies to traffic announcements.

A 'Y' indicates that a station has TMC within the RDS.

Only in-use technical parameters are currently provided for DAB transmitters. Their RF parameters are organised in the same way as for analogue, although DAB transmissions are vertically polarised only. The main differences from analogue are in the make-up of the programme content, and the network structure. A DAB ensemble (or multiplex) will carry an identical set of audio (and possibly data) services across its coverage area, and the spreadsheet has columns for up to 15 audio and 15 data services, which are filled from the left.

The ensemble will normally be broadcast from a number of transmitters on the one frequency; this is known as a single frequency network (SFN). Certain makes of radio enable the listener to identify which particular transmitter within an SFN is the dominant one in a given area, which can be useful in orientating receive aerials. Each transmitter carries its own transmitter identification (TII) codes and these two digit 'main' and 'sub' codes are also included in the spreadsheet, but be warned that they are stored in ‘hexadecimal' form, so you may need to convert them if your radio presents them in 'decimal'.

These documents were originally published by the Radio Authority, one of the organisations replaced by Ofcom at the end of 2003. They represent Ofcom's current policy.

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