Independent Local Radio is proud of the good audio quality of its programmes. The modern equipment and the IBA Codes of Practice help to achieve that but so does the enthusiasm and determination of everyone connected with ILR To gain full benefit from these transmissions you need good receivers, sensible aerials, and a little knowledge.

Listeners who appreciate good audio quality are advised, wherever possible, to use the VHF/FM service rather than medium waves. The use of VHF/FM gives a significant improvement: better fidelity; better dynamic range of sound; far less local electrical interference or interference from other stations, by day or night; and a constant level of reception summer and winter.

The large number of stations and changes in the upper atmosphere at night (which brings in distant stations as 'interference') mean that it is not possible to provide high fidelity broadcasting on medium waves. But medium waves do have some advantages: they enable simple receivers to be used and allow easier reception in cars. You do not automatically obtain 'high fidelity' by listening to VHF/FM - It needs good quality loudspeakers and amplifiers and an effective aerial to do that - and also care in tuning. But VHF/FM usually gives lower 'background' noise, is less susceptible to electrical interference, and allows you to listen in stereo if you wish: something not available on medium waves.

Medium-wave receivers almost invariably have an in-built aerial in the form of a coil wound on a ferrite rod. This is a convenient and usually effective aerial. Such aerials are directional, and by turning the set it is often possible to minimise interference and/or obtain best reception.

The older style of outdoor or indoor wire aerial and earth is seldom used today except by enthusiasts seeking distant stations. However, where sets or tuners have an 'earth' socket then an earth wire may reduce electrical interference and sometimes reduce 'hum'.

To receive broadcast stereo, a dual-channel amplifier is needed and two loudspeakers; a 'stereo decoder' is normally part of a stereo receiver.

A stereo signal occupies a wider channel; it is more susceptible to interference from other stations and needs a significantly stronger minimum signal than mono It is usually no use making do with an odd piece of wire or an in-built set aerial: good 'hiss-free' stereo needs an outdoor or at the very least a loft aerial with two (sometimes more) elements properly installed. Even so, there are bound to be a few places, at the limit of the service area, where listeners can get satisfactory mono but just cannot get rid of all the 'hiss' on stereo. A good outdoor aerial may also be advisable to help overcome 'multipath distortion' due to reflected signals. Some VHF/FM directional aerials do not work well above 100 MHz and it is worth asking any aerial installer to make sure that he is fitting one of the newer designs intended for use up to 108 MHz.

Domestic systems need to be correctly arranged to obtain full benefit of stereo. The two loudspeakers should be placed some feet apart, and the listener hears the correct stereo effect when sitting roughly an equal distance from the two speakers, with an unobstructed view of them.

Sometimes it is easier to obtain good results by listening on modern stereo headphones; this retains the sense of spaciousness and the directional effects, although if a listener turns his or her head the whole sound environment turns.

BBC FM RECEPTION ADVICE:

FM radio (sometimes known as VHF) offers high quality listening and stereo sound but it can sometimes be spoiled by reception problems and interference. Most of these problems are well known and can be dealt with easily to enable you to get the most out of FM broadcasts. The information below describes the most common problems and tells you what you can do about them.

Weak Signal - Hiss

If your radio hisses on stereo but not on mono it could be because it is receiving too weak a signal. This happens because radio receivers need a stronger signal to successfully decode the stereo component of the signal than for just the mono component. To solve this problem you need a good aerial, correctly positioned to pick up the best possible signal. Ideally it should be mounted outdoors, like a TV aerial. If really necessary an amplifier can be fitted to the aerial in order to boost a signal which is weak, for example, because it is attenuated by a very long downlead. If your radio receiver is portable with no provision for plugging in an external aerial, try adjusting the position of the radio's own aerial by tilting and swivelling it to get the best signal, (see Fig 1). If this fails, try moving the radio to somewhere else in the room because FM reception can vary a great deal over very short distances. It is often better near windows and may also be better upstairs than downstairs.


Multipath Distortion

Multipath distortion is characterised by the specific distortion of  's' and 'z' sounds (sibilants) such that 's' sounds like 'shhh'. In its more serious forms it effects all the sounds to make them rough sounding or 'brittle'. It is caused, as the name implies, by the transmitted signal travelling to the receiver via more than one path: a common cause of this is reflection of the signal from hills or tall buildings, (see Fig 2). The reflected signal arrives at the aerial a moment later than the direct one because It has travelled further. The reflected and direct signals then interfere with each other causing distortion.

The best way to minimise multipath distortion is to use a directional rooftop aerial, i.e. one which will only pick up signals coming from the direction of the transmitter, and will reject reflections which arrive at its sides or its back. It is also sometimes possible to mount the aerial so that the house screens it from the reflections but not from the wanted signal. If you have a multipath distortion problem with a portable radio try moving it to a different position in the room.


Adjacent Channel Interference

Adjacent channel interference is interference from a channel which is close in frequency to the one on which you are listening. It sounds like a twittering noise in the background and is consequently sometimes known as 'birdies'. The problem is usually only apparent on stereo but if the interfering channel is very close in frequency, i.e. only 50 or 100 kHz away, the effect may also be heard in mono.

The BBC's FM transmitter network has been designed to avoid such problems but if you are listening outside the published service area of the transmitter, or if  there are rare atmospheric conditions, you could still suffer from this problem.

As with most reception problems, a good directional rooftop mounted aerial will probably solve the problem, providing the interfering transmission is not coming from the same direction as the transmission you want. Some stereo tuners incorporate 'birdie' filters which use electronic circuitry to block out adjacent channels.

Overloading

Overloading happens when a FM receiver receives too strong a signal. It should only be a problem if you live close to the FM transmitting station. Overloading causes intermodulation distortion which very rough and discordant and this in turn will cause twittering 'birdies' in the

background. The distortion will be present both in stereo and in mono. The cure for overloading is to fit an attenuator between the aerial and the receiver. Attenuators are available from radio and TV shops and they are easily plugged in between the aerial and the aerial socket. They come in various values, quoted in decibels (dB), and your, dealer should be able to advise you on the correct amount of attenuation you require.

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