Front-End For Fm Receiver

EE " 988 69 FRONT-END FOR FM RECEIVER Among the most important technical characteristics of a VHF preamplifier are the noise figure, and the large signal handling capability. Although these are in principle conflicting requirements, a compromise can be found in the use of high-quality RF components. The re- ceiver"s ability to withstand high input levels can be enhanced by providing suf- ficient selectivity ahead of the active el- ement(s). This is especially important for the mixer, since it generates most in- termodulation products. In this FM tunerhead, the aerial signal is first passed through a slightly over- critically coupled band filter, amplified with the aid of low noise UHF transistor Ti, and again filtered. The overall gain between the aerial input and the mixer input is about 12 dB at 87 MHz, and 17 dB at 108 MHz. The difference is caused by the adopted method of filter coupling. A wideband Schottky DBM (double balanced mixer) is used for the mixer in this design. The...