Radio Experimenter Theory Notes

Receivers

Sensitivity

This is the ability of a receiver to receive weak signals. The gain can usually be adjusted with the RF gain control.

Selectivity

This is the ability to receive one signal and disregard others on adjacent frequencies. This is very important on the crowded amateur bands.

Bandwidth

A receiver with high selectivity is said to have a narrow bandwidth.

Frequency Stability

This is the ability of a reciever to remain tuned to the desired signal. If the receiver is not stable, it is said to drift.

Automatic Gain Control

This is the automatic control of the sensitivity of the receiver by the strength of the signal to which it is tuned.

TRF (Tuned Radio Frequency) Receiver

This is probably the most simple and basic of receivers. The TRF receiver consists of three basic parts.

RF AMPLIFIER
The purpose of the RF amplifier is to select and amplify the required incoming signal.

DETECTOR
This converts the incoming RF signal to audio frequency. It also provides feedback near the signal frequency to allow reception of CW.

AF AMPLIFIER
This stage amplifies the output from the detector to a level where it can drive a loudspeaker

The TRF receiver suffers from poor selectivity which means that it is not a lot of use in present day amateur radio.