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Radio receivers

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Types Of Radio Receiver
Sensitivity and Selectivity
Frequency range

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Radio receivers

  1. 1. Contents  Introduction  History  Types Of Radio Receiver  Sensitivity and Selectivity  Frequency range
  2. 2. Introduction  A radio receiver is an electronic device that receives radio waves and converts the information carried by them to a usable form.
  3. 3. History  Alexander Stepanovich Popov  First radio receiver in 1896.  It was based on electromagnetic waves,  which were proven to exist by James Clerk Maxwell only a few years earlier in 1887.
  4. 4. Types Of Radio Receiver Crystal radio receiver Tuned radio frequency receiver Superheterodyne Receiver
  5. 5. Crystal radio  A crystal radio is the simplest kind of radio  It needs no battery or power source  It gets all of its power only from the radio wave.
  6. 6. Components of Crystal Radio  Antenna  Tuner  Coil  Ground wire  Detector  Capacitor  Diode
  7. 7. Working
  8. 8. Tuned radio frequency receiver  one or more tuned radio frequency (RF)  individually tuned to the station's frequency
  9. 9. Tuned Radio Frequency Receiver  A tuned radio frequency receiver (or TRF receiver) is a type of radio receiver that is usually composed of one or more tuned radio frequency (RF) amplifier stages followed by a detector (demodulator) circuit to extract the audio signal and an audio frequency amplifier. Popular in the 1920s, it could be tedious to operate because each stage must be individually tuned to the station's frequency. By the mid 1930s it was replaced by the superheterodyne receiver invented by Edwin Armstrong.
  10. 10. How it works  The classic TRF receivers of the 1920s and 30s consisted of three sections:  One or more tuned RF amplifier stages. These amplify the signal of the desired station to a level sufficient to drive the detector, while rejecting all other signals picked up by the antenna  a detector, which extracts the audio (modulation) signal from the radio carrier signal by rectifying it  optionally, but almost always included, one or more audio amplifier stages which increase the power of the audio signal.
  11. 11. Advantages and disadvantages  Disadvantage.  Since they used inductor and capacitor as tunning the element, the circuit is bulky and costly.  They are not suitable to amplify audio frequencies  If the band of the frequency is increased, design become complex.
  12. 12. Advantages and disadvantages Advantages  They amplify defined frequency.  Signal to noise ratio at output is good.  They are well suited for radio transmitters and receiver.  The band of frequency over which amplification is required can be varied.
  13. 13. Superheterodyne Receiver  Antenna  RF(Radio Frequency)  Mixer  Local Oscillator(LO)  IF(Intermediate Frequency)  Detector  Audio amplifier  Power amplifier  Speaker
  14. 14. Architecture of Superheterodyne Receiver Antenna The antenna pick up all radiated signal and feeds them into the RF(Amplifier) .These signal are very small (usually only a few microvolts).
  15. 15. RF(Amplifier)  This circuit can be adjusted (tuned) to select and amplify any carries frequency within the AM Broad cost band . Only the selected frequency and its two side bands pass through the amplifier.(Some AM Receiver don’t have a Separate RF amplifier stage.)
  16. 16. Local Oscillator This circuit generates a steady sine wave at a frequency 455 khz above the selected RF
  17. 17. Mixer Intermediate Frequency fIF = fRF ± fLO RF=1000Khz LO=1455Khz fIF=2455, fIF=455
  18. 18. IF Amplifier Increase the level of the signal . Demodulation The received signal is now processed by the demodulator stage where the audio signal (or other baseband signal) is recovered and then further amplified. Audio Amplifier This circuit amplifies the detected audio signal and drive the speaker to drive sound
  19. 19. Sensitivity and Selectivity  Sensitivity Weak signal  noise  Selectivity  Band width filter  1% of RC Frequency
  20. 20. How radio waves travel.  Although radio waves are sometimes colloquially referred to as "airwaves", they do not require air or any other medium in which to travel and can travel through a vacuum.  Like light waves, radio waves travel in straight lines unless something reflects or refracts them. Like light waves, radio waves may be obstructed by obstacles, which can cast a radio "shadow". Although radio waves can pass through many non-conductive material without much loss, they do suffer some loss when passing through walls, floors and roofs. This loss depends upon the building materials used and increases at higher frequencies. Metal, water, ground and other electrically conductive materials cause large losses to radio waves passing through them and in some cases no usable signal may pass through.
  21. 21. Frequency range  A radio receiver may be designed to tune to a fixed frequency,  MF AM broadcast band, 535 kHz - 1605 kHz  General coverage MF/HF communications receiver 100 kHz - 30 MHz  VHF FM broadcast band, 88 - 108 MHz  UHF TV broadcast band (analogue or digital) 470 - 860 MHz  Scanning receiver 0.5 MHz - 1300 MHz  GSM 900, GSM1800 or 3G mobile phone bands  Wireless LAN band 2400 - 2483.5 MHz