simple fm test generator

The need occasionally arises for an FM test generator for the repair or alignment of VHF FM tuners or re- ceivers. However, unless the constructor is something of an H.F. fanatic the cost of a sophisticated commercial generator is not justified in view of its limited ap- plications. The simple generators described in this article will enable a wide range of tests to be carried out on both the front end and the i.f. strip, at relatively little cost. In both the circuits described the r.f. oscillator is an astable multivibrator with a 1 0. 7 MHz ceramic filter in the coupling to determine the frequency of oscillation. Frequency modulation is carried out with a varicap diode, and due to the high harmonic content of the output a useful signal is available in the VHF band as well as at the 10.7 MHz fundamental. torola CMOS 2-of-8 Tone Encode