Trying to send and receive.
Now that we have the antenna (dipole) we can try to send and receive some messages. The first thing that we can do is to think at a code (Morse code) where each letter of the alphabet is coded into points and lines. When we want to send a point we close for a short time a switch and we transmit a sinusoid, when we want to send a line we close the switch for a longer time. At the receiver we put an oscilloscope connected to the receving dipole and when we see a short sinusoid we "decode" it like a point and when we see a longer sinusoid we relate it to a line.
There is a problem, in the pauses between the points and lines we don't see the oscilloscope in the zero state, why? Because we see all the electromagnetic noise that belongs from the human industrial activities and from the nature. If we are too far from the transmitter, that noise can cover our desidered signal. We can' t think to amplify it because we amplify also the noise. We observed that there is more noise in the low frequencies due to the fact of real impulse. We defined the ratio between the signal and the noise (S/N) and also the minimum detectable signal (related to the minimum power that i need in reception if i want to obtain some information).
If we are too far from the transmitter we can think to change the antenna with one that is more directive (eg. Yagi-Uda or parabolic).
In the end we saw the definition of dB and dBm and we applied it at the formula of received and trasmitted power. We also observed these definition (dB and dBm) in real datasheets of some commercial antennas.
Nessun commento:
Posta un commento