User:Chetvorno/work2

‎How receivers work ← Previous revision Revision as of 06:44, 23 June 2016 Line 692: Line 692:   ==How receivers work==   ==How receivers work==   Almost all radio receivers perform these three functions:   Almost all radio receivers perform these three functions: − *''Bandpass filtering'': The receiver uses a [[bandpass filter]] to select the radio signal of the desired radio transmitter from the multiple radio signals picked up by the antenna. In radio communication, radio waves from multiple transmitters can pass through the air simultaneously without interfering with each other because they have different [[frequency|frequencies]], that is, the [[carrier wave]] of each transmitter oscillates at a different rate. The receiver's antenna typically receives a broad range of frequencies, so in addition to the desired radio station's signal, the oscillating voltage from the antenna may contain signals from other transmitters, as well as [[radio noise]] ([[radio frequency interference|RFI]]). To separate out the desired radio transmission, the bandpass filter passes the frequency of the radio station and blocks signals at all other frequencies. The information (modulation) in the radio transmission is contained in a narrow band of frequencies around the carrier frequency, so the filter has to pass a specific band of frequencies. The band of frequencies received by the receiver is called its ''[[passband]]''. + *''Bandpass filtering'': The receiver uses a [[bandpass filter]] to select the radio signal of the desired radio transmitter from the multiple radio signals picked up by the antenna. In radio communication, radio waves from multiple transmitters can pass through the air simultaneously without interfering with each other because they have different [[frequency|frequencies]], that is, the [[carrier wave]] of each transmitter oscillates at a different rate. The receiver's antenna typically receives a broad range of frequencies, so in addition to the desired radio station's signal, the oscillating voltage from the antenna may contain signals from other transmitters, as well as [[radio noise]] ([[radio frequency interference|RFI]]). To separate out the desired radio transmission, the bandpass filter passes the frequency of the radio station and blocks signals at all other frequencies. The information (modulation) in a radio transmission is contained in a narrow band of frequencies around the carrier frequency, so the filter has to pass a specific band of frequencies. The band of frequencies received by the receiver is called its ''[[passband]]'',     − :The bandpass filter performs this filtering by using [[resonant circuit]]s (tuned circuits). A simple resonant circuit is composed of an [[inductor]] (coil of wire) and a [[capacitor]] connected together. It has a natural [[resonant frequency]] similar to a [[tuning fork]] When an oscillating + :The bandpass filter consists of [[resonant circuit]]s (tuned circuits). A simple resonant circuit is composed of an [[inductor]] (coil of wire) and a [[capacitor]] connected together. It has a natural [[resonant frequency]] similar to a [[tuning fork]], which is set equal to the frequency of the desired radio station. At its resonant frequency the resonant circuit has a high [[impedance]], so the radio signal from the desired station is passed on to the following stages of the receiver. At all other frequencies the tuned circuit has low impedance, so signals at these frequencies are conducted to ground and not passed on. − **''Tuning'': Some receivers (for example those in [[garage door opener]]s and [[radar]] sets) are fixed to receive a single transmitter on a single frequency, but most receivers (such as AM and FM broadcast receivers), are adjustable so they can receive different transmitters on different frequencies. ''Tuning'' is the process of adjusting the frequency of the receiver's passband to the frequency of the desired radio transmitter. In many modern receivers such as [[television set]]s this is accomplished automatically by pressing a "channel up" or "channel down" button, but other receivers use the traditional method of turning a "tuning" knob until the desired station is heard in the speaker. The range of frequencies a receiver can be tuned to is called its tuning range. For example, [[FM receiver]]s cover the [[FM band]] of frequencies, from 88 MHz to 108 MHz in the US. + **''Tuning'': Some receivers (for example those in [[garage door opener]]s and [[radar]] sets) are fixed to receive a single frequency, but most receivers (such as AM and FM broadcast receivers), are adjustable so they can receive different transmitters on different frequencies. ''Tuning'' is the process of adjusting the frequency of the receiver's passband to the frequency of the desired radio transmitter. In many modern receivers such as [[television set]]s this is accomplished automatically by pressing a "channel up" or "channel down" button, but other receivers use the traditional method of turning a "tuning" knob until the desired station is heard in the speaker. The range of frequencies a receiver can be tuned to is called its tuning range. For example, [[FM receiver]]s cover the [[FM band]] of frequencies, from 88 MHz to 108 MHz in the US. − *''Amplification'': The power received by an antenna decreases with the square of its distance from the transmitting antenna. Even with the powerful transmitters used in radio stations, if the receiver is more than a few miles from the transmitter the power intercepted by a receiver's antenna is very small, in the range of microwatts or nanowatts. In order to increase the + *''Amplification'': The power of radio waves picked up by a receiving antenna decreases with the square of its distance from the transmitting antenna. Even with the powerful transmitters used in radio stations, if the receiver is more than a few miles from the transmitter the power intercepted by the receiver's antenna is very small, in the range of [[microwatt]]s, [[nanowatt]]s or [[picowatt]]s. In order to increase the power of the signal to a level capable of driving the [[loudspeaker]] or [[earphone]], electric power from a [[battery]] or wall socket is used to [[amplifier|amplify]] the signal.   *''Demodulation'': After the radio signal is filtered and amplified, the receiver must extract the information-bearing [[modulation]] signal from the radio frequency [[carrier wave]],   *''Demodulation'': After the radio signal is filtered and amplified, the receiver must extract the information-bearing [[modulation]] signal from the radio frequency [[carrier wave]],