The TF 2300A Modulation Meter is primarily for measurement of f. m. deviation but it also measures a. m. depth. With its wide range of deviation frequency, modulation bandwidth and carrier frequency, this instrument is suitable for application to fixed and mobile point-to-point communications, broadcasting, telemetry and multi-channel link equipment in the h. f. , v. h. f. and u. h. f. bands. Distortion and channel separation tests on f. m. stereo receivers and 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. A. M. depth can be measured up to 95% in a 30 Hz to 15 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, crystals can be switched in to control the local oscillator, or an external local oscillator may be used. The instrument can be operated without a local oscillator for measurements in the 1-2 MHz range. The instrument can be operated from mains power or a nominal 24 V battery. Voltage regulation eliminates transformer tap changing except between 115 V and 230 V ranges. On battery, the regulation compensates for battery voltage variations between 21.5 and 30 V. Transistorized circuits consuming little current give reasonable length of operation onbatteryfor mobile purposes.