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Why the strength of the carrier in FM spectrum is not constant?
Wiki User
∙ 14y ago
You can think of it this way:
When the FM carrier is modulated, you know that "sidebands" appear in the frequency spectrum,
at frequencies both above and below the carrier frequency. These are new signals, with energy
being transmitted at each sideband frequency.
But the power out of the transmitting hardware hasn't changed. Unlike the case with AM, the
modulation process most likely takes place in a low-level stage of the transmitter, and the
modulator supplies no RF power.
Since new signal energy appears at new frequencies separated from the carrier frequency,
the energy has to come from somewhere. No RF energy is added in the transmitter, so the
sideband energy comes out of the carrier signal.
That's a very unscientific and un-mathematical way to look at it, but I don't think it's
essentially inaccurate.
Wiki User
∙ 14y ago
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What is the difference between FM and AM radio waves?
AM means Amplitude(=height) modulation, so the frequency stays the same and the message is coded into variations of the strength of the signal. FM stands for Frequency modulation. Here the strength of the signal stays the same and the message is coded into changes in frequency instead.
What is essential bandwidth of FM signal?
"Essential bandwidth" is the portion of the signal spectrum that encompasses most of the energy of the original signal in the frequency domain.
What is the highest and lowest radio signals that your radio signals that your radio can pick up for AM and FM?
Radio signals have several characteristics ... wavelength, field strength, amplitude, advertising cost,popularity, frequency, etc. The question doesn't specify which characteristic it wants measured in orderto name the "highest" and "lowest".We'll assume it's referring to the frequency of the various radio signals.In the USA, commercial AM broadcast stations all have carrier frequencies between 0.55 MHz and 1.7 MHz.Typical consumer AM radios are designed to operate across that range.In the USA, commercial FM broadcast stations all have carrier frequencies between 88 MHz and 108 MHz.Typical consumer FM radios are designed to operate across that range.
Conclusion about amplitude modulation?
A carrier is used to make the wavelength smaller for practical transmission and to permit multiplexing. The spectrum is used to measure bandwidth (the range of frequencies) and the efficiency (the power in the side-bands compared to the total power) Bandwidth can be predicted using BW = 2 fm where fm = the maximum modulating frequency Efficiency depends only on the modulating index, m (the fraction of the carrier you modulate by) AM is limited to 33% efficiency because the modulation index cannot be increased to > 1.0 without introducing distortion in the receiver.
What factor determines the spacing of the sidebands in an amplitude modulated signal?
Its a function of the signal bandwidth. If you modulate a 1 MHz carrier with a 1 KHz sine wave, you will see three peaks in the frequency domain - the carrier - the carrier minus 1 KHz - and the carrier plus 1 KHz. If the carrier is 100 MHz, the spacing is still the same, unless you consider spacing to be proportional to the carrier frequency - but that does not seem to be the question. Improved. Bandwidth is a function of modulating frequency in simple Amplitude Modulation. As described above, 1 MHz signal with 1 kHz modulation creates a lower side frequency (1000 - 1) = 999 kHz, the carrier = 1000 kHz and the upper side frequency 1001 kHz. These two side frequencies exist up to the point of 100% modulation. Over 100% modualtion, large numbers of extra side frequencies ("Splatter") will exist. Since we rarely use single-tone modualtion, but a spectrum of modulating frequencies, the upper and lower energy appears within the two side bands - commonly called sidebands. The composite signal now comprises a lower sideband, which (for a maximum modulating frequency Fm) extends "down" to Fc-Fm, the carrier (Fc), and the upper sideband, which extends "up" to Fc+Fm. Be aware that advanced AM techniques, such as SSB-SC and VSB may use half the bandwidth of full-carrier, both-sidebands AM. Also, be aware that AM techniques used in digital data (QAM, Trellis coding, etc) processing differ from the "audio/broadcast" descriptions above.
When was Spectrum FM created?
Spectrum FM was created in 1996.
What is the effect of varying frequency of the carrier signal on the AM wave?
spread spectrum , modulation or depending on the bandwidth poss FM (deviation)
FM is better than AM?
FM is frequency modulation. The amplitude is held constant and the carrier frequency is varied. AM is amplitude modulation. The amplitude is varied and the carrier frequency is held constant.
What is the Total amount of spectrum used by the FM stations in Chennai?
what is the total amount of spectrum used by the FM stations in Chennai?
How does the frequency change in a FM transmitter?
-- the modulation index varies -- the instantaneous deviation varies -- the amplitude of the carrier component varies -- the spectrum of sidebands varies -- the total occupied bandwidth varies
What happens to the power in the carrier after frequency modulation?
In FM the carrier is still present and the power is still there, at a constant amplitude at the transmitter. It's only the frequency of the carrier that alters, in time with the audio applied to it. The louder the sound the further the frequency shifts.
What is the difference between FM and AM radio waves?
AM means Amplitude(=height) modulation, so the frequency stays the same and the message is coded into variations of the strength of the signal. FM stands for Frequency modulation. Here the strength of the signal stays the same and the message is coded into changes in frequency instead.
What is the wave frequency of an FM radio wave?
FM radio is transmitted anywhere in the spectrum of 88Mhz to 108Mhz
What extracts the intelligence from a high frequency carrier in FM receivers?
One method to extract the intelligence (signal) from a high frequency carrier in FM receivers is with a phase locked loop.
What is Modulation index in Frequency modulation?
Modulation Index is the ratio of the maximum deviation frequency to the frequency of modulation. In other words it is the ratio of the spread in frequency spectrum to the frequency that was used to modulate the carrier. For FM, modulation index is given by the formula mf= df/f where, mf=modulation index for FM df=difference in carrier frequency f=frequency of the signal
What is fast frequency hopping?
This is also known as spread spectrum. It's a method of encoding a signal using a changing carrier frequency. FM radio is incoded using a single carrier frequency which is varied slightly to encode the information. Think of frequency hoping as FM, but with the carrier changing quickly. So instead of staying on 88.1, the signal starts on 88.1, then jumps to 95.2, then to 101.3, then to 81.5, etc. etc. Each transmitting and receiving device knows the pattern of carrier jumps, so it knows where to look for the information. This is how bluetooth works.
Difference between FM and PM?
frequency of the carrier is varied in accordance to the message signal in FM. Fm receivers are less complex. in Fm lower frequencies produce variation to the modulation index. phase of the carrier is varied in accordance to the message signal in PM. Pm receivers require proper synchronization so it is complex. Modulation index is independent of audio frequency
