6.2. THE TUNED CIRCUIT

fig. 37

The signal at the terminals of the aerial consists of a mixture of signals of all the surrounding radio stations as shown in fig. 37.

But we want to listen only to one of those stations.

How to sort out one single station?

All of them carry audiosignals, - but this fact does not help us here... (Audiosignals are all of the same frequency spectrum). On the other hand all of them have a carrierfrequency as well. And those carrierfrequencies are - for sure different from each other (otherwise the radiostations would be operated against the law). So we can sort the desired program out, by letting through to the next stages of our receiver only the radiosignal with the carrierfrequency of our desired radio station.

The circuit which will be able to do this filtering is the so called TUNED CIRCUIT and it consists of at least one capacitor and an inductor. How the filtering is achieved really, we will discuss in details later in chapter 6., at this stage of explanation it is just important to keep in mind, that we will find in each radio at least one of those tuned circuits connected right to the terminals of the aerial.