Receiver Principles

Question 0

What are the 4 main receiver characteristics

Answer 0

Sensitivity

Selectivity

Stability

Noise

Question 1

Name 3 requirements of an efficient receiver

Answer 1

Able to select the wanted signal from all other signals available at its input

Able to extract intelligence contained in the modulated signal

Able to produce an output of sufficient power to operate the output transducer

Question 2

What do RF, IF and AF stand for? And what are they?

Answer 2

RF - Radio Frequency - the carrier signal

IF - Intermediate Frequency - the intermediate step in the process of heterodyning (turning RF into AF)

AF - Audio Frequency - a frequency audible to the human ear (between 20 and 20,000 hertz)

Question 3

What is the process of converting a Radio Frequency (RF) into an Audio Frequency (AF) called?

Answer 3

Heterodyning

Question 4

What is the purpose of a filter?

Answer 4

It allows the receiver to select a wanted signal/signals or frequency/frequencies available from all other signals or frequencies available at its input, whilst rejecting all others

Question 5

What are the 5 types filter called and what are their effects?

Answer 5

Low pass filter

High pass filter

Band pass filter

Band reject filter

Notch filter

Question 6

In relation to filters, describe what is meant by passbands and stopbands

Answer 6

Passband - the frequencies that are allowed through/retained by the filter and appear in the output signal

Stopband - the frequencies that are rejected/removed by the filter and do not appear in the output signal

Question 7

Describe Gain

Answer 7

Gain is the ratio/difference between input and output values

Gain is measured in decibels

Likening to volume is sufficient

Question 8

What does AGC mean and what does it do?

Answer 8

AGC - Automatic Gain Control - AGC reacts to surging and fading of a signal and adjusts the gain in a receiver to keep the output at a constant (in terms of power/volume)

Question 9

What is meant by attack time and decay time?

Answer 9

Attack time - the time taken for an AGC system to react to variations in input signal level

Decay time - the time taken for an AGC system to stop reacting to variations in input signal level

Question 10

Describe Squelch

Answer 10

Squelch excludes undesired lower power input signals (or noise) that may be present at or near the frequency of the desired signal

The cut off point or threshold may be known as false noise floor