|Radio and Electronics (DED Philippinen, 66 p.)|
|6. RECEPTION OF RADIOSIGNALS (AM - TYPE)|
Electronic devices consist nowadays in most cases of a lot of different circuits, each of it having a special purpose playing a special role in the oncert of the whole device. Each of the circuits itself can be very complicated.
To visualize the function of such devices, it would be far too confusing if we would draw all the components and interconnections in those different circuits at once.
Therefore nowadays more and more another method of visualization is used: the so-called BLOCK DIAGRAMM.
Here each different circuit playing a special role is symbolized by only a block (a rectangle carrying a special symbol or a word explaining the function). The blocks are interconnected by lines which show the flow of the signals or of energy from one block to the other.
Using this method of visualization we can draw at this stage of explanation a block diagram of the parts of a radio which we have come to know already.
Fig. 38 shows what we can draw up to now. Additional to the normal blockdiagramm, we find in this drawing the type of signal, appearing between those blocks.
If you have a closer look to the output signal of the tuned circuit you will find, that it is exactly the signal which would leave the transmitter of the radiostation we want to listen to.
But you should know: this drawing showing an ideal situation Normally you will have a huge attenuation on the way from the radiostation to the receiver, and the signal leaving the tuned circuit is very small (often less than a milli Volt).
If we receive the signal of a radiostation very near by (let us say a few hundred meters) this signal would be - with some luck - a few hundred milli Volts.
A sensitive earphone can produce sound with such a low voltage, but KEEP IN MIND: EVEN IF THE OUTPUT SIGNAL OF THE TUNED CIRCUIT IS POWERFUL ENOUGH YOU CANNOT LISTEN TO IT BY CONNECTING AN EARPHONE DIRECTLY.