SUBJECT: RADIO AM FM
AM MODULATION PRINCIPLES
modulation is called the effect of "add" a low frequency signal (information) to a high frequency or carrier.
There are three basic methods of modulating the carrier. Are amplitude modulation, modulation Frequency and phase modulation. In our case we will study the amplitude modulation.
Figure 1 shows a wave of radio frequency (RF) pure AF signal and an amplitude modulated wave signal AF
The amplitude of the RF signal varies with modulating signal amplitude. Moreover, the speed with which varies the amplitude of the RF signal depends on the frequency modulation signal.
A RF signal is called a carrier and the envelope or modulating AF.
modulation rate
.- Relationship tension between BF and RF voltage is designated as the degree of modulation, represented by the letter m. The degree of modulation in% is given by the formula:
% modulation = Vmax-Vmin x 100
Vmax + Vmin
The degree of modulation is chosen so that the signal does not reach BF to modulate the carrier by more than 100%, on the maximum amount the 90% modulation.
ISSUER SYSTEM .-
is responsible for transmitting the signal into space. Consists of the following blocks:
- sound signal converter power, which is the modulating signal.
- Oscillator carrier, which will be responsible for generating a frequency wave pattern that has the station.
The degree of modulation is chosen so that the signal does not reach BF to modulate the carrier by more than 100%, on the maximum amount the 90% modulation.
ISSUER SYSTEM .-
is responsible for transmitting the signal into space. Consists of the following blocks:
- sound signal converter power, which is the modulating signal.
- Oscillator carrier, which will be responsible for generating a frequency wave pattern that has the station.
modulator, we mix the two signals, the LF and RF, giving us the amplitude modulated signal.
RF Amplifier us conveniently amplify the signal to pass through space.
RECEIVER SYSTEM .-
receptor occurs in the reverse process of modulation (Fig. 3). This process is called demodulation or detection.
The desired station signal is received by the antenna and selected by the RF switch. Then it is detected. The resulting audio signal is amplified and applied to the speaker.
superheterodyne receiver .-
The previous recipient was overwhelmed by the superheterodyne receiver. This is more practical because it provides more selectivity, sensitivity and stability. The building blocks of a receiver of this type are:
a) input circuit, which is done by coupling the antenna to the first transistor and is tuned to the frequency of the station you want to receive fs.
b) local oscillator, which generates the frequency signal Buddha, that to achieve the effect heterodyne, must be mixed (broken) with the received signal. The frequency of this oscillator is variable at will and must maintain a constant difference, IF of 460 KHz, with the signal tuned input circuits (fs).
d) mixer, in which the two heterodyne signals fs and Buddhas. Normally the same way makes local oscillator and mixer then called converter.
e) Intermediate Frequency, which consists of one or more amplifier stages tuned to the IF frequency of 460 KHz. This amplifier between the different frequencies that occur in the heterodyning and are present at the output of the converter, selects and amplifies only the FI.
d) detector, which demodulates the IF, thus obtaining
BF signal that is modulated. This detector must receive the IF signal strong enough to work in the linear area of \u200b\u200bthe characteristic of the diode, so there is no distortion.
usually derived from a component detector for continuous operation of AGC (Automatic Gain Control).
The previous recipient was overwhelmed by the superheterodyne receiver. This is more practical because it provides more selectivity, sensitivity and stability. The building blocks of a receiver of this type are:
a) input circuit, which is done by coupling the antenna to the first transistor and is tuned to the frequency of the station you want to receive fs.
b) local oscillator, which generates the frequency signal Buddha, that to achieve the effect heterodyne, must be mixed (broken) with the received signal. The frequency of this oscillator is variable at will and must maintain a constant difference, IF of 460 KHz, with the signal tuned input circuits (fs).
d) mixer, in which the two heterodyne signals fs and Buddhas. Normally the same way makes local oscillator and mixer then called converter.
e) Intermediate Frequency, which consists of one or more amplifier stages tuned to the IF frequency of 460 KHz. This amplifier between the different frequencies that occur in the heterodyning and are present at the output of the converter, selects and amplifies only the FI.
d) detector, which demodulates the IF, thus obtaining
BF signal that is modulated. This detector must receive the IF signal strong enough to work in the linear area of \u200b\u200bthe characteristic of the diode, so there is no distortion.
usually derived from a component detector for continuous operation of AGC (Automatic Gain Control).
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