sentences:  Radio receivers is the fourth topic that covers the principles and operation of TRF receivers and Superheterodyne receivers, CW reception; with receiver characteristics such as sensitivity, selectivity and fidelity; Adjacent-channel interference and image interference; AGC and squelch; and signal to noise ratio (S/R).Similarly, the next topic on transmitters covers the principles and operation of low power transmitters; oscillators such as the Colpitts oscillator, Hartley oscillator, crystal oscillators, and stability of oscillators.The last three topics deal with radio propagation, aerials, and frequency measurement.