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Download Free PDF. A short summary of this paper. Amplitude modulation is a technique used in electronic communication most commonly for transmitting information via a radio carrier wave. This is achieved by varying the strength of the carrier signal in relation to the information being sent. Hence, the changes in the maximum and minimum values of carrier signal result to the varying modulating index at 0.
Introduction shouting. An attempt to propagate speech in free space comes up against two very severe obstacles. The first is A radio signal can be generated by causing an similar to that of the transmitters discussed earlier, in electromagnetic disturbance and making suitable which they interfere with each other because they share arrangements for this disturbance to be propagated in free the same medium of propagation.
The second obstacle is space. The equipment normally used for creating the due to the fact that low frequencies, such as speech, disturbance is the transmitter, and the transmitter antenna cannot be propagated efficiently in free space whereas ensures the efficient propagation of the disturbance in free high frequencies can. Unfortunately, human beings cannot space. To detect the disturbance, one needs to capture hear frequencies above 20 kHz which is, in fact, not high some finite portion of the electromagnetic energy and enough for free space transmission.
Hence, the envelope detector is also called as the diode detector. The low pass filter contains a parallel combination of the resistor and the capacitor. In the positive half cycle of AM wave, the diode conducts and the capacitor charges to the peak value of AM wave. When the value of AM wave is less than this value, the diode will be reverse biased. Thus, the capacitor will discharge through resistor R till the next positive half cycle of AM wave.
When the value of AM wave is greater than the capacitor voltage, the diode conducts and the process will be repeated. You will not be kept responsible for DSP processes. However, you can find them very useful when comprehending sampling rate, rate conversion, Finite Impulse Response FIR , decimation and interpolation etc.
You can also check the following resource:. Now, we will go one further step to transmit a music file, and then receive it via USRP hardware. In this case the transmission is real time, therefore unlike the simulations, you will observe the noise through the air. You will find them very useful while answering prelab questions and comprehending lab tasks. The passband received signal after the demodulation is converted to baseband.
This process is simply:. Connect the AWGN channel. Set the variance from mask as 0. What do you observe in each case? Comment your result. Taub, D. Principles of Communication Systems 3rd ed. McGraw Hill. Boulmalf, Y. To achieve this, we should choose mx t small as compared to unity 1 for all values of t. If m is small, then, the AM wave is weak.
This means that the distortion in the detector output is low if and only if the applied AM is weak and if the percentage modulation is very small. The envelope demodulator is a simple and very efficient device which is suitable for the detection of a narrowband AM signal. A narrowband AM wave is the one in which the carrier frequency f c is much higher as compared to the bandwidth of the modulating signal.
An envelope demodulator produces an output signal that follows the envelope of the input AM signal exactly. It is used in all the commercial AM radio receivers. In every positive half cycle of the input, the demodulator diode is forward biased and charge the filter capacitor C connected across the load resistance R to almost the peak value of the input voltage.
The capacitor will now discharge through R between the positive peaks as shown in fig.
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