Chapter 10

R.F. and I.F. amplifiers

Introduction

The amplifiers discussed so far have had a passband beginning at zero or a very low frequency and extending over several octaves. Such a passband is termed the baseband and baseband amplifiers are characterised by their use of direct or RC inter-stage couplings (aperiodic couplings, in fact). We shall now consider amplifiers in which the passband is small compared with the mid-band frequency. Here LC circuits can be used as coupling elements. If the r.f. signal to be amplified is sinusoidal and of fixed frequency, the passband can be made as narrow as desired: this is possible in the carrier-wave amplifiers in transmitters. If, however, the r.f. signal is modulated, the passband must be wide enough ...

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