Independent Broadcasting Authority

Engineering information for Radio Hallam


The IBA's Responsibilities

The Independent Broadcasting Authority Act 1973, which consolidates the Television Act 1964 and the Sound Broadcasting Act 1972, provides the legal

framework for the setting-up of Independent Local Radio stations under the control of the Independent Broadcasting Authority.

The iba is thus responsible for both Independent Television (itv) and Independent Local Radio (ilr). For both it selects and appoints the programme companies; supervises the programme planning; controls the advertising; builds, owns, and operates the transmitters; provides distribution links; and establishes technical standards.

By March 1974 thirteen of these stations were either on the air or contracts had been offered by the Authority. In July 1974 the Home Secretary announced that six more stations would be authorised, bringing the total to nineteen, further developments depending on Lord Annan’s Committee on the Future of Broadcasting.

Each programme will be transmitted simultaneously on medium wave (mf-am) and Band II (vhf-fm). It is hoped that local radio audiences will come to accept vhf as the main listening service as soon as possible, with mf fulfilling a matching role, especially during daylight hours. The vhf-fm transmissions will have a stereo capability; details are given below.

The new radio stations, so far as possible, provide a service specifically aimed at their local communities, and in order to do this the men and women who produce the programmes need to be closely identified with their localities. The programming schedules seek to provide a reflection of life in the area through entertainment, news, information, and education; the specialist news company in London provide a prime source of national and international news, both for its own transmission area and for supply to the other radio companies.

As with Independent Television, the radio companies are self-supporting. Advertisement revenue is the prime means of financing Independent Broadcasting and one of the Authority’s major functions is the control of the amount, presentation and content of advertisements. The iba’s Code of Advertising

Standards and Practice has been revised to encompass sound broadcasting. Under the provisions of the Independent Broadcasting Authority Act 1973, no programme sponsorship or advertising magazines is permitted. The maximum time allowed for radio advertising is nine minutes in any one clock-hour.

The Authority received two applications for the ilr programme contract for the Sheffield and Rotherham area. Both applicants were interviewed by an iba group which visited Sheffield in February 1974. The group also met representatives of the civic, educational and religious life in the area and individual members of the public. Further interviews were held in London; and in March 1974 the Authority announced their selection of Radio Hallam Limited. The programme plans which were submitted as part of Radio Hallam’s successful application to the iba were published on the day the station commenced broadcasting.

Radio Hallam Ltd

P.O. Box 194, Hartshead, Sheffield S1 1GP.
Tel: Sheffield (0742) 71188

G. F. Young, C.B.E., J.P. (Chairman); W.S. MacDonald; Mrs D. DeBartolome; Lord Darling; J.P. Graham; J. J. Jewitt, J.P.; T. P. Watson, J.P.; H. Witham.

G. Blincow (Company Secretary); K. Skues (Programme Director); M. Lindsay (Production Manager); Jean Doyle (Woman’s Editor); D. Turner (Features Editor); I. Rufus (News Editor); S. Linnell (Sports Editor); D. Adams (Sales Promotion Manager); J. Orson (Chief Engineer)


Stereophonic Broadcasting

The conductor taps the podium twice. Sounds begin to swell and fill the auditorium. The movement builds up to a momentous crescendo.

An evening at the concert hall. We hear a collection of sounds all reaching our ears from different directions.

Each performer contributes his own part. Stereophony can create these sensations in the home. All types of music, live or on today’s excellent recordings, and drama productions are brought to life by stereo.

The stereo effect

Our television or portable radio provides us with just one source of sound via the loudspeaker. Even though the quality may be very good, we have no idea of movement or direction of sound — as we have in the theatre or concert hall, or as popular music makers are able to create electronically in their recordings. Stereophony requires at least two sound channels, and consequently the same number of loudspeakers. But by carefully positioning the loudspeakers and listeners, the directions and movements of sound can be simulated. Thus adding realism and greatly increasing our listening enjoyment.

Two channel stereo can be provided by stereo record players or tape recorders. Sound broadcasting in the vhf band is also capable of providing the two channels. Independent Local Radio broadcasts many programmes in stereo (on vhf). By obtaining the necessary stereo receiver, amplifier and loudspeakers you can add a new dimension to your listening enjoyment.

How stereo broadcasting works

The two separate sound channels used for stereophonic broadcasting are often called the ‘A’ and ‘B’ channels. One way to broadcast stereo would be to transmit the A and B channels individually. This has the disadvantage that listeners with single channel (‘monophonic’) receivers would have to tune into one or other of the two channels. In fact, they need a single channel composed of a mixture of the A and B channels. Also, two channels would occupy a large amount of precious vhf spectrum space.

The Pilot Tone System

The ‘pilot tone’ system used by ilr and many other broadcasting organisations overcomes these problems. A composite signal is broadcast, which is arranged to contain two parts. One is the ‘sum’ of the A and B signals, that is A+B. The second is the ‘difference’,

A—B. The arrangement (of the two parts) is such that listeners with mono receivers receive only the A—B signal – which is the mixture they require. And listeners with stereo receivers obtain the individual A and B channels – by adding and subtracting the A+B and A—B signals electronically within their stereo receiver.

The Decoder

The part of the stereo receiver which adds and subtracts the ‘sum’ and ‘difference’ signals is called the decoder. In fact some mono vhf receivers can be converted to stereo by the addition of a suitable stereo decoder. Your dealer will be able to advise you on this.

An advantage of ILR VHF transmissions

Most ilr vhf transmissions are ‘circularly polarized’ This is a term which describes the way in which the radio waves emanate from the transmitting aerial. The iba is the first broadcasting organisation in the uk to use this method. One result of this is better reception for most vhf car radio users. But it’s worth noting that in general stereo reception needs a much larger signal than mono reception, so you may need a more efficient aerial system. It really depends on where you live. Your dealer will be able to advise you on this.

Choosing stereo equipment

There are no hard and fast rules for choosing stereophonic receiving equipment. An extensive choice is available, covering a wide range of styles, quality and prices. The best way to choose is to listen to as many systems as possible within your budget. Then select the system which you think sounds most realistic in comparison with a live performance.


When you have purchased your stereo receiving system, take care in positioning your loudspeakers and listeners. This is very important — otherwise the stereo effect may be partially lost. The loudspeakers should be placed as far apart as possible, up to a

maximum of about twelve feet. Listeners should sit near the centre line between the two loudspeakers. Now you can take your seat….

For stereo reception the need for a good, carefully positioned aerial is well worth emphasising if you are to achieve the best results from your stereo receiver.

If you need any further advice on reception of ilr transmissions, the Engineering Information Service of the iba will be pleased to answer your queries. The addresses are:

Independent Broadcasting Authority,
Engineering Information Service,
Crawley Court, Winchester, Hants SO21 2QA.
Tel: Winchester 822444
and for London subscribers,

Independent Broadcasting Authority,
Engineering Information Service,
70 Brompton Road, London SW3 1 EV.
Tel: 01-584 7011, and ask for Engineering Information.


The Pilot-Tone System


A Hand Audio Channel – After pre-emphasis 
B Right Hand Audio Channel – After pre-emphasis
M Compatible Signal – to which monophonic’ receivers respond
S Modulus of Stereophonic Sub-Channel
𝓌 Pilot Tone Angular Frequency

Technical Description

The Independent Local Radio vhf service employs the Pilot-tone system, as defined by C.C.I.R. Recommendation 450 (Vol V, Part 1, New Delhi, 1970).

The compatible signal, M, equal to one half the sum of A and B, produces a deviation of the main carrier of not more than 90% of the maximum permissible deviation, 75kHz. A separate signal, S, equal to one half the difference between A and B, is used to obtain the sidebands of an amplitude-modulated suppressed sub-carrier, whose frequency is 38kHz. The sum of these sidebands produces a peak deviation of the main carrier of the same amount as the signal S would give if applied in place of the M signal, i.e. not more than 90% of the maximum permissible deviation, 75kHz. A pilot signal, whose frequency is 19kHz, i.e. one half that of the suppressed Sub-Carrier, is arranged to produce a deviation of the main carrier of between 8% and 10% of the maximum, 75kHz.

The instantaneous deviation of the main carrier is given by the following expression

fd = 0.9 (M+S.sin 2𝓌t+0.1 sin 𝓌t) ✕ 75kHz


𝓌∕2π=19kHz, M=½(A+B) and S=½(A–B).

A and B are restricted to the range of ±1 and consequently neither ½(A+B) nor ½(A–B) can fall outside the range ±1. The component ½(A+B), or M, represents the compatible monophonic signal. It is the only component available for monophonic reception.

The component ½(A–B), or S, represents the difference signal. It enables a stereophonic receiver to separate the A and B signals since M+S=A and M–S=B. The phase relationship between the Pilot-tone and the suppressed sub-carrier may be discerned from the above expression for fd. It is such that when modulating the transmitter with a multiplex signal for which A is positive and B=–A, this signal crosses the time axis with a positive slope each time the pilot signal has an instantaneous value of zero. A positive value of the multiplex signal corresponds with a positive deviation of the main carrier. The Pilot-tone is readily filtered out at the receiver and is used to regenerate the 38kHz Sub-Carrier to allow recovery of the S signal.

Since the values of A and B are each restricted to ±1, the expression for fd cannot exceed the range ±75kHz, which is the requirement for maximum deviation of the main carrier.

Pre-Emphasis Time Constant (for each channel): 50µs
Pilot Tone Frequency: 19,000±2Hz
Stereo Sub-Carrier Frequency: 38,000±4Hz
Pilot Tone Phase Stability: ±3°
Residual Sub-Carrier: <1%


IBA Transmitters

VHF Transmitters–FM with stereo capability

MF Transmitter–AM Mono only

Tapton Hill
NGR SK 324 870
95.2 MHz e.r.p. 0.1kW
Horizontal Polarization
Aerial height 950 ft. a.o.d.

NGR SK 432 913
95.9 MHz e.r.p. 0.05kW
Circular Polarization
Aerial height 435 ft. a.o.d.

Skew Hill
NGR SK 327 934
194 m  1546 kHz
Transmitter power 400W

Regional Engineer: H.N. Salisbury
Tel: 0532 33711

Engineer-in-charge: I. C. I. Lamb, MBE

The map shows the area within which most listeners with vhf monophonic receivers should obtain satisfactory reception. Good stereo reception should also be obtainable by the majority of listeners, provided adequate aerials are installed. 

The axes on the map relate to NGR co-ordinates