Tuners exhibit great variability in their technical performance. We are interested not only in aspects of a tuner's sound, but also in more basic characteristics such as the ability to pick up weak or distant stations, reject adjacent stations, provide a noise-free audio signal and stay tuned to a station without drifting.

A tuner's performance in these areas can be accurately characterised by technical measurements and this makes tuner specifications much more meaningful than those of other audio components.

Good tuners are characterised by, first of all, their sensitivity or the ability to pull in weak stations. The greater a tuner's sensitivity, the better it can pick up weak stations. This aspect of a tuner's performance is more important in suburban areas that are far from radio transmitters.

Tuner sensitivity, called usable sensitivity, is defined by specifying the voltage across the antenna in millivolts, usually 1.7 millivolts. The lower the sensitivity specification the better, as less signal is required for good reception.

Sensitivity is different for mono and stereo reception - mono requires less RF signal strength to achieve a specified sensitivity. In fact, a tuner may require more than double the signal strength to achieve the same sensitivity in stereo than in mono. Good tuners should have a sensitivity of 13 millivolts (stereo) and 1.6 millivolts (mono), which have signal strength enough for 40 to 50 kilometres from radio transmitters.

Channel separation between the left and right channels is another important factor as it correlates with increased spaciousness in the sound. Figures between 30-50dB are regarded as a great stereo separation.

A tuner characteristic of greater importance to the city dweller is selectivity: the ability to pick up one station without interference from the station next to it on the dial. The selectivity defines a tuner's ability to reject a strong station two channels away from the desired channel.

When stations are packed closely together, as they are in cities, selectivity and channel separation are more important than sensitivity. By the way, a tuner that has 60-70dB selectivity is considered to have efficient rejection of adjacent station interference. The reason is that low sensitivity sometimes decreases a tuner's signal-to-noise ratio, increasing noise signals.

A tuner with a poor signal-to-noise ratio will overlay the music with an annoying background hiss. A poor tuner will have trouble receiving weak stations and may lack the ability to select one station when that station is adjacent to another station that gives high background noise.

Finally, a good car stereo tuner is not much use without a good antenna to pick up the signal in the first place.

By Wijit Boonchoo