Abstract :
The paper describes the design and operation of certain instruments used specifically for work upon frequency modulation equipment and can be conveniently divided into four sections. In the first section signal generators are discussed and it is shown that these can be sub-divided into two classes as (a) those that use the ¿beat frequency oscillator¿ principle, and (b) those that employ harmonic generation. The advantages and disadvantages of both systems are summarized and a brief description is given of one typical f.m. signal generator. The second section deals with detection equipment and in particular with the design of deviation meters. As these instruments are required to give a faithful indication of the amplitude and fidelity of an f.m. wave, a discriminator circuit having inherent low distortion and high stability is essential. It is then shown how the pulse counter type discriminator meets these requirements and how this circuit may be incorporated into a complete deviation meter. Frequency modulation transmission monitoring equipment is dealt with in the third section, the requirements being discussed and typical performance figures given for each item in the equipment. The paper concludes with a section on spectrum analysis. It is shown that spectrum analysers essentially consist of two individual units, a swept oscillator and a cathode ray display unit. Two methods are given, one electronic, the other mechanical, for producing the required sweep. The complete apparatus is then described and some applications are outlined which include, in particular, the visual analysis of f.m. waveforms.
