Datasheet

FM Radio Essentials
www.kitronik.co.uk/2157
Improving the Radio Tuning
Tuning the radio using the potentiometer can be a tricky task. This is because one turn of the potentiometer covers
the whole frequency range. This means that only very small adjustments of the potentiometer are required to tune
into the different stations.
Large Dial
One way to improve the tuning mechanism is to attach a large dial to the end of the potentiometer. Look at the two
dials below. As the smaller dial has a circumference six times smaller than the large dial, it would take six time the
travel on the larger dial to achieve the same degree of change than if you used the smaller dial. This would therefore
make fine tuning the radio six times easier.
Using a Pulley to give Mechanical Gearing
Another solution is to use a pulley system to improve the tuning mechanism. Take the system shown below. In this
arrangement the larger pulley would be attached to the tuning potentiometer and the smaller dial would be used to
make the tuning adjustments. As the smaller dial (pulley) has a circumference six times smaller than the large pulley,
it would take six full rotations of the smaller dial to give one full rotation of the larger pulley. This would therefore
make fine tuning the radio six times easier than if the small pulley had been connected directly to the tuning
potentiometer.
Using both a Pulley System and a Large Dial
Of course and even better solution would be to add a large dial in front of, but on the same shaft that the small
pulley/dial in the above diagram is attached to. That way you would get the benefit of both systems this would give
thirty six times better adjustment.
Dial / Pulley
circumference = 12cm
45 degree adjustment = 1.5cm travel
Dial / Pulley
circumference = 2cm
45 degree adjustment = 0.25cm travel
Dial
circumference = 2cm
Pulley
circumference = 12cm
Potentiometer