crystal3.mpg

In part 3, we discover that our simple crystal set does not work on the medium wave band. All the stations are jumbled together. Improvements need to be made. The first step is to couple in our aerial (antenna) via a variable capacitor. This enables us to get the desired signals better, by avoiding the 'damping effect' caused by the unwanted capacitance of the aerial. Still, results are not totally satisfactory. In order to completely separate the 3 strong nearby radio stations we can receive, we have to isolate the bad effects of the aerial still further, while of course retaining the signals it brings to us! This is achieved by giving the aerial its own completely separate circuit. The signals from this are coupled into our resonant circuit (a 'rejector' circuit) by coupling between the two coils (inductors). And at last we can completely separate the three incoming signals. But there is a price to pay for this: each separate signal is now very weak. Part 4 will attempt to follow in the footsteps of early radio constructors, as they strove to increase the strength of these hard-won separate radio signals.