Modulation of waves (Communication Systems)

In summary, the conversation discusses the process of amplitude modulation and its use in converting AC into DC. It also touches on the use of a rectifier and low-pass filter to demodulate the signal and remove the high frequency component. The conversation also mentions the use of a capacitor to remove the DC component and the application of an electrical transducer in communication systems involving cables and EM waves transmission. The original question asks about the effect of limiting the oscillations of the transmitted wave to one quadrant and its impact on efficiency. The answer is that it does not affect efficiency and the demodulation process still applies.
  • #1
Prashasti
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Please look at the attachments below.
I shall use the word "modulation" instead of "amplitude modulation" since I've been taught about AM only.
So, my question is, in the first image (that I've attached), the messenger wave (which is modulated with the high frequency carrier wave) as well as the modulated wave, both are shown to be varying with time - and their phase is also changing (just like ALTERNATING CURRENT).

So, this is the wave which is transmitted.

But, in the second image - which shows the fate of the transmitted wave after being received by the receiver antenna- the output wave is shown to be varying with time - but its phase is not changing (i.e. The variations are limited to one quadrant only - above the axis only ) - just like time varying DC.

So, 1) Can the arrangement be used to convert AC into DC?
2) Is the change acceptable? I mean - the input wave's phase was changing - but it is not so with the output wave. So, will it affect the efficiency? Like- in the case of a voice signal?
20141226_174517.jpg
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  • #2
The amplitude modulated signal received with the antenna, goes through a rectifier which transmits only the positive half of the signal. (The rectifier can be a diode, which transmits that part of the signal which makes the diode open ...) The result is a fast varying signal, with slowly changing height. Using a low-pass filter, it removes the high frequency component and you get the demodulated signal, that corresponds to the modulating one.
 
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  • #3
Prashasti said:
and their phase is also changing (just like ALTERNATING CURRENT).
There is no changing phase shift in the AM signal that I can make out, not like in FM. The demodulation block diagram applies to the AM signal, and shows the negative half of the waveform being removed, followed by filtering. The filtering function can even be considered to be performed by the audio amplifier or the loudspeaker, since neither will respond to the RF component in the rectified wave.
 
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  • #4
NascentOxygen said:
There is no changing phase shift in the AM signal that I can make out, not like in FM. The demodulation block diagram applies to the AM signal, and shows the negative half of the waveform being removed, followed by filtering. The filtering function can even be considered to be performed by the audio amplifier or the loudspeaker, since neither will respond to the RF component in the rectified wave.

I got the point. But still I think I didn't get the answer of the 'original' question. Actually, I'm trying to say that in the second diagram, all the oscillations are confined to one quadrant only - I mean, the wave is not "crossing" the time axis...Whereas in the first one, it can be seen actually crossing the time axis and entering in a different quadrant (like a sine wave).
 
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  • #5
And please help me with my first question too...(marked as 1) in the original post).
If this question seems to be pointless - then please explain the working of a transducer..Since It's not clear to me.
Is an electrical transducer used only in the case of a communication system involving cables (eg. The 'basic' telephones - landline) or is it also used in the systems involving EM waves transmission (eg. Mobile phones)?
 
  • #6
Prashasti said:
I got the point. But still I think I didn't get the answer of the 'original' question. Actually, I'm trying to say that in the second diagram, all the oscillations are confined to one quadrant only - I mean, the wave is not "crossing" the time axis...Whereas in the first one, it can be seen actually crossing the time axis and entering in a different quadrant (like a sine wave).
A capacitor will remove the DC component and return the recovered message wave to being centred on zero. Most audio amplifiers have capacitive coupling, so the DC component is removed there, if not before.
 
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  • #7
Prashasti said:
And please help me with my first question too...(marked as 1) in the original post).
If this question seems to be pointless - then please explain the working of a transducer..Since It's not clear to me.
Is an electrical transducer used only in the case of a communication system involving cables (eg. The 'basic' telephones - landline) or is it also used in the systems involving EM waves transmission (eg. Mobile phones)?
Sorry, I don't understand this. Perhaps you mean "modulator" (or maybe "detector") where you wrote "transducer"?
 

1. What is modulation and why is it important in communication systems?

Modulation is the process of varying a carrier signal in order to transmit information. It is important in communication systems because it allows for the efficient transfer of information through different mediums, such as air or wires.

2. What are the different types of modulation techniques used in communication systems?

There are several types of modulation techniques, including amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM). Other more complex techniques include quadrature amplitude modulation (QAM) and pulse code modulation (PCM).

3. How does modulation affect the range and quality of a communication signal?

Modulation can affect the range and quality of a communication signal in several ways. For example, different types of modulation have different ranges and are suitable for different types of transmission. Additionally, the quality of a signal can be affected by external factors such as interference or noise.

4. What is demodulation and why is it necessary?

Demodulation is the process of extracting the original information from a modulated carrier signal. It is necessary in order to decode the transmitted information and make it usable for the receiver.

5. How has modulation technology evolved over time?

Modulation technology has evolved significantly over time, from simple analog techniques to more complex digital methods. With advancements in technology, modulation techniques have become more efficient, allowing for faster and more reliable communication.

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