Post by Progenitor A on Feb 18, 2011 8:56:44 GMT 1
Introduction
Amplitude Modulation
Amplitude modulation is a common way of transferring low frequency information carried on the back of a high frequenct 'carrier'
For example a celestial 'pulsar' flashing on and off is an amplitude modulated light source - the signal varies from a maximum to zero.
In general , mathematically an AM waveform can be represented by:
x=(a + b)sin At)sinBt
where At = 2pifct and fc is the high frequency carrier
and Bt = 2pifit and fi is the low frequency information
(THERE IS NO NEED TO UNDERSTAND THE MATHS TO ANSWER THIS MULTI-CHOICE QUESTION!)
Frequency Modulation
FM is a much better way of conveying low frequency information on a high frequency carrier. Instead of varying the amplitude of the signal with the information, we vary the frequency of the signal
Celestial examples of FM include binary stars where one star is rotating around another. What we sometimes see is the apparant frequency of the light varying - toward th ered as one binary is accelearted away from us and toward the blue end of the spectrum when it is accelerating towrad us. A more commonplace example is Radio 4 FM that uses the same principle but at lower carrier freqyencies
In general, mathematically, an FM wave can be represented as:
x(t) = Xc·cos [Act + β·sin (Bmt)]
Where, Act = 2pifct where fc is the carrier frequency
and
Bmt)= 2pifmt where fm is the information frequency
β= a constant
(THERE IS NO NEED TO UNDERSTAND THE MATHS TO ANSWER THIS MULTI_CHOICE QUESTION!)
Remember that in AM the amplitude of the modulated wave varies
and in FM the frequency of the modulated wave varies.
OK
The Multi-Choice Question
a)
In an FM wave the carrier amplitude remains constant and the frequency varies
b)
In an AM wave the amplitude of the carrier varies and it frequency remains constant
c)
In an FM wave the carrier amplitude varies and its frequency remains constant
d)
In an AM wave the carrier remains constant and its frequency remains constant
Amplitude Modulation
Amplitude modulation is a common way of transferring low frequency information carried on the back of a high frequenct 'carrier'
For example a celestial 'pulsar' flashing on and off is an amplitude modulated light source - the signal varies from a maximum to zero.
In general , mathematically an AM waveform can be represented by:
x=(a + b)sin At)sinBt
where At = 2pifct and fc is the high frequency carrier
and Bt = 2pifit and fi is the low frequency information
(THERE IS NO NEED TO UNDERSTAND THE MATHS TO ANSWER THIS MULTI-CHOICE QUESTION!)
Frequency Modulation
FM is a much better way of conveying low frequency information on a high frequency carrier. Instead of varying the amplitude of the signal with the information, we vary the frequency of the signal
Celestial examples of FM include binary stars where one star is rotating around another. What we sometimes see is the apparant frequency of the light varying - toward th ered as one binary is accelearted away from us and toward the blue end of the spectrum when it is accelerating towrad us. A more commonplace example is Radio 4 FM that uses the same principle but at lower carrier freqyencies
In general, mathematically, an FM wave can be represented as:
x(t) = Xc·cos [Act + β·sin (Bmt)]
Where, Act = 2pifct where fc is the carrier frequency
and
Bmt)= 2pifmt where fm is the information frequency
β= a constant
(THERE IS NO NEED TO UNDERSTAND THE MATHS TO ANSWER THIS MULTI_CHOICE QUESTION!)
Remember that in AM the amplitude of the modulated wave varies
and in FM the frequency of the modulated wave varies.
OK
The Multi-Choice Question
a)
In an FM wave the carrier amplitude remains constant and the frequency varies
b)
In an AM wave the amplitude of the carrier varies and it frequency remains constant
c)
In an FM wave the carrier amplitude varies and its frequency remains constant
d)
In an AM wave the carrier remains constant and its frequency remains constant
