The Dymar AM/FM Modulation Meter Type 1785 is an all solid state instrument for the measurement of depth of modulation or frequency deviation of transmitters. It is operated either from A. C. Mains or from its own rechargeable battery and as much is equally suitable as a laboratory instrument or as a portable field servicing equipment. The frequency range covered is the whole of the V.H.F. band and extends into the U.H.F. band to include the mobile band of 470 MHz. The sensitivity over the whole of this range is better than 2.5 mV in 50 ohm (-40 dm) which permits loose coupling to the transmitter under test. The instrument is specifically designed for measurement of narrow deviation transmitters in todays mobile and portable radiotelephones, the most sensitive deviation being 3 kHz. The local oscillator has low residual F. M. noise of typically 44 db below 3 kHz. Auxiliary outputs are provided both at the Intermediate Frequency (500 kHz) for viewing the modulation envelope and at Audio Frequency for measurement of distortion.