Subelement F: Receivers— Topic 43: Oscillators
Question 3-43F6
Element 3 (GROL)In Figure 3F15, which block diagram symbol (labeled 1 through 4) is used to represent a local oscillator?
Explanation
Symbol 2, a circle with an arrow pointing out, is the standard block diagram representation for an oscillator or a signal source. A local oscillator (LO) is a circuit that generates a stable, continuous radio frequency (RF) signal. In receivers, this signal is mixed with the incoming RF signal to convert it to an intermediate frequency (IF). In transmitters, the LO often generates the carrier wave or a frequency used in frequency conversion stages.
Symbol 1 typically represents an antenna or a general input/output connection. Symbol 3, a plain square/rectangle, is a generic processing block like a filter, mixer (if it has an 'X'), or other stage. Symbol 4, a triangle, universally represents an amplifier. Therefore, only symbol 2 accurately depicts a local oscillator.
Related Questions
3-43F4 Which type of oscillator circuit is commonly used in a VFO (variable frequency oscillator)?3-43F5 What condition must exist for a circuit to oscillate? It must:3-44F1 What is the image frequency if the normal channel is 151.000 MHz, the IF is operating at 11.000 MHz, and the LO is at 140.000 MHz?3-44F2 What is the mixing process in a radio receiver?3-44F3 In what radio stage is the image frequency normally rejected?