RF circuit design (3) - VHF amplifier

EE 40 April 1986 Fig I. Represen- tation of FM band spectrum analyses showing that the noise factor of the pre- amplifier stage determines to a large extent the number of sta- tions that can be made audible in the FM receiver. Some of the important aspects in aerial amplifier design have already been covered in Elektor Electronics, March 1986 issue, along with the prerequisites for successful VHF filter realization. While the points discussed in that article remain fully valid, the present article aims to look at the most important technical characteristic of any VHF preampli- fier stage: its noise figure. While many of today"s FM tuners have very sophisticated tuning con- trol systems and excellent stereo demodulation, the design of up-to- date RF amplification and first mixer sections often deplorably lags behind. Since it is certainly not ad- visable to embark upon a complete reshuffle of the proprietary RF parts in the receiver front end, an add-on preamplifier stage of good d...