 to what people could afford. A regenerative detector works by feeding back some of the signal from the output to the input. A control called a regeneration or reaction control is used to keep the circuit just below the point of oscillation. At this point the maximum usable gain is achieved. The other advantage of this type of circuit is that it also improves the response of the tuned circuit, making it sharper and improving its Q. The 'Q' or quality factor of a tuned circuit is a measure of the performance of a tuned circuit. It is defined as the resonant frequency divided by the bandwidth of the points where the response has fallen by 3 dB. If the regeneration control is advanced SO that the circuit oscillates the receiver is then able to resolve Morse and single sideband signals. The oscillation in the detector beats with a Morse signal to give the characteristic tone. For a single sideband signal it replaces the carrier SO that the original audio can be recovered at the detector. If a regenerative detector is used then it should be preceded by a radio frequency amplifier. This isolates the oscillation generated in the detector from the antenna. If no RF amplification is present then the oscillation can be radiated or transmitted from the antenna and it can cause interference to others nearby. Regeneration Feedback or reaction control Regenerative amplifier detector amplifier Figure 5.4 Block diagram of a tuned radio frequency receiver with regeneration Receivers 123 Direct conversion receiver One type of radio that has gained popularity over the years and is now widely used as a simple yet effective solution for a variety of applications is the direct conversion set. As its name suggests it uses a process which directly converts the radio frequency signal down to audio frequencies for amplification. The basic process used in the direct conversion receiver is a process called mixing. This is not like audio mixing where several signals are added together in a linear fashion to give several sounds together. Radi