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• Radio wave


  One of the most studied members of the Electromagnetic Spectrum
• Radio receiver


  • An electronic device that receives and converts the desired radio waves back to audio or visual information
• Sensitivity


  Identifies and amplifies signals at the input of the receiver, tells the weakest signal that a receiver will be able to identify and process
• Types of radio receivers

  • Tuned radio frequency (TRF) receiver
  • Supersonic heterodyne radio receiver
• TRF receiver


  1. Tuned radio frequency stages

  2. Signal detector

  3. Audio amplifier
• The TRF receiver gained popularity in 1920's, however the tuning took a little while for each stage in the early radios requires separate adjustment
• The standard frequency of the IF signals for amplitude modulation (AM) radio tuner is 455 kHz, (Kilohertz), or 455,000 Hertz, (Hz). These are the same for all AM radio tuners.
• Heterodyne process or heterodyning process


  The process of mixing two different signals to produce a new signal or signals
• This process is used in all radio receivers, and that is why all radio receivers are often called superheterodyne radio receivers.
• Intermediate Frequency (IF) Section

  • It is like an electronic gate
  • When the 455 kHz IF signal arrives, it automatically opens to permit this 4bb kHz IF signal to pass through and enter the radio tuner
  • When other signals whose frequency is not 455 KHz attempts to enter, the IF section automatically blocks this signal
  • The IF section prevents interfering signals to enter the radio tuner when it is tuned to one radio station
• Typically, there are three intermediate frequency transformers (IFTs) used in the IF section. Between the second IFT and third IFT is the second IF amplifier transistor.
• Intermediate Frequency Transformers (IFTs)

  • They are made of two small wires wound around the adjustable ferrite core and enclosed in a metal shield
  • The adjustable ferrite cores are adjusted during the aligning process of the radio tuner
• Detector


  Also called the demodulator. Its work is to detect and recover the audio information from the radio signal received by the radio tuner.
• The separated and recovered audio information or signal is then fed to the audio amplifier where it is amplified or strengthened sufficiently; the detector is usually made of a small crystal diode.
• In this FM receiver, the de-emphasis network (Low pass filter) is included after the FM demodulator. This signal is passed to the audio amplifier to increase the power level. Finally, we get the original sound signal from the loudspeaker.
• Figure 5 shows an example of a tuned circuit
• Tuned circuit


  1. Antenna captures radio waves

  2. Waves pass through a series of RF amplifiers

  3. RF amplifier is composed of a resonant circuit, a combination of an inductor and a capacitor
• The resonant circuit is also known as a tuned circuit
• Ganged tuning


  All RF amplifiers tuned to signal a single frequency
• Tuning


  Changing the frequency through mechanical or electrical means
• Adding one more tuned circuit allows the selection of one station at a time
• Increasing one or more turned circuits will increase the selectivity of the radio receiver
• Tuned amplification


  • Increased sensitivity
  • Increased selectivity
• Detector


  1. Reconstructs the information carried by the radio waves

  2. Process of extracting the original information from the carrier wave is called demodulation

  3. Diode, capacitor, and resistor make up the detector circuit

  4. Removes high-frequency components

  5. AM demodulation has two stages: rectification by a diode, capacitor smooths out the amplitude of the rectified signal
• Audio frequency (AF) amplifier

  1. Amplifies the weak signal drives the signal to the loudspeaker or an output device

  2. Increases the signal high enough to drive loads of devices

  3. Speaker is used to hear the audio signal in the form of sound
• TRF receivers


  • Easier to design
  • High sensitivity allowing broadcast frequency from 535 kHz to 1705 kHz
  • Problems: difficulty in designing at very high frequency, poor audio quality, instability, and poor selectivity
• Supersonic heterodyne wireless receiver was developed to provide an additional level of selectivity
• Superheterodyne receiver


  1. Uses a heterodyne or mixing process to convert signals done to a fixed intermediate frequency

  2. Tuning is through the effective changing of the local oscillator

  3. Broadcast radio receivers, televisions, short wave receivers, and commercial radios have used the superheterodyne principle
• The superheterodyne was used in every form of radio from domestic broadcast radios to walkie talkies, television sets, through to hi-fi tuners, and professional communications radios, satellite base stations, and much more
• Superheterodyne receiver system


  1. Receiving antenna captures and transforms radio waves to an intermediate frequency (IF)

  2. RF amplifier amplifies the IF signal and sends it to the mixer

  3. Local oscillator provides a signal to mix with signals coming from the antenna

  4. Mixer generates an output signal which contains the sum and difference of the frequency of the two inputs

  5. Only the difference frequency or the IF is of interest

  6. Detector reconstructs the information brought by the IF signal

  7. Some frequencies are rejected, due to the selectivity in the IF amplifier

  8. AM broadcast band has the standard IF is 455 kHz, FM broadcast and television broadcast bands have standard IFs of 10.7 MHz and 44 MHz, respectively

  9. Output from the detector may need amplification

  10. Speaker is required to listen to the speech or music carried by the signals
• Amplitude Modulation (AM)


  The frequency of the signal is constant, but the amplitude or height of the signal varies
• The standard frequency of the IF signals for amplitude modulation (AM) radio tuner is 455 kHz, (Kilohertz), or 455,000 Hertz, (Hz). These are the same for all AM radio tuners.
• Heterodyne process or heterodyning process


  The process of mixing two different signals to produce a new signal or signals
• This process is used in all radio receivers, and that is why all radio receivers are often called superheterodyne radio receivers.
• Intermediate Frequency (IF) Section

  • It is like an electronic gate
  • When the 455 kHz IF signal arrives, it automatically opens to permit this 4bb kHz IF signal to pass through and enter the radio tuner
  • When other signals whose frequency is not 455 KHz attempts to enter, the IF section automatically blocks this signal
  • The IF section prevents interfering signals to enter the radio tuner when it is tuned to one radio station
• Typically, there are three intermediate frequency transformers (IFTs) used in the IF section. Between the second IFT and third IFT is the second IF amplifier transistor.
• Intermediate Frequency Transformers (IFTs)

  • They are made of two small wires wound around the adjustable ferrite core and enclosed in a metal shield
  • The adjustable ferrite cores are adjusted during the aligning process of the radio tuner
• Detector


  Also called the demodulator. Its work is to detect and recover the audio information from the radio signal received by the radio tuner.
• The separated and recovered audio information or signal is then fed to the audio amplifier where it is amplified or strengthened sufficiently; the detector is usually made of a small crystal diode.
• In this FM receiver, the de-emphasis network (Low pass filter) is included after the FM demodulator. This signal is passed to the audio amplifier to increase the power level. Finally, we get the original sound signal from the loudspeaker.