The TF 230OB Modulation Meter measures f.m. deviation and a.m. depth. With its wide range of deviation frequency, modulation bandwidth and carrier frequency, the instrument is suitable for application to fixed and mobile point-to-point communications, broadcasting, telemetry and multi-channel link equipment in the h.f.s v.h.f. and u.h.f. bands. Distortion and channel separation tests on f.m. stereo transmitters can also be made. Positive and negative f.m. deviation can be measured in ranges from 1.5 kHz to 500 kHz full- scale at modulation frequencies between 30 Hz and 3.4 kHz on the 1. 5 kHz deviation range, and 30 Hz and 200 kHz on all other deviation ranges. AM depth can be measured up to 95% in a 30 Hz to 50 kHz modulation bandwidth. Either f.m. or a.m. can be measured in the presence of the other. Although measurements are normally made by means of the meter readout, i.f. and demodulated outputs are available at the front panel for examination or analysis. Spurious a.m. and f.m. due to hum and noise are kept to a level insignificant for most applications but, where required, an optional crystal oscillator can be fitted, or an external local oscillator may be used. The instrument can be operated without a local oscillator for measurements in the 1 to 2 MHz range.