Since its introduction a few years ago the model 77-380 has proved to be on of the most outstandingly successful pieces of measuring equipment ever produced. This fact has been attested by thousands of satisfied users throughout Canada, the U.S.A. and Europe. In producing this revised version of the 77-380, it has been the intention to improve on the efficiency of the well proven original circuit, and to extend the range of usefulness still further by providing a greater frequency coverage. Stability has been considerably improved by the use of a very fine variable air spaced band setting trimmer, while by the use of a unique coil tapping arrangement, spurious responses have been eliminated but with no sacrifice in the selectivity for which the 77-380 is famous. The sensitivity of the new unit when used as a modulation indicator has been greatly improved allowing considerably reduced coupling to the transmitter as a result. In addition, modulation checks can now be carried out with the unit in a resonant condition, that is, with appropriate coil in circuit and tuned to the frequency in question. In this condition even greater sensitivity is provided on modulation checks.