fet front

The frequency counter design published in the November 1975 issue of Elektor was accompanied by a design for an input preamplifier (Elektor 8, December 1975 p. 1235). Whilst this design gave good performance from 0-20 MHz it was decided that for r.f. work a preamp with a higher sensitivity would be useful, since it is here that signal levels are smallest. To avoid problems due to input cable capacitance the preamp is equipped with a FET input probe.