INTRODUCTION FM/AM Modulation Meter type TF 2304 has been designed primarily for the servicing and production line testing of mobile radio transmitters. It covers the frequency bands most commonly used forfixed and mobile communications and particular attention has been paid to the provision of facilities and accessories required for the field testingof mobile equipment. The instrument incorporates automatic tuning over the carrier frequency range of 9 to 12.5 MHz and 18 to 1000 MHz and also provides automatic level control provided the input signal to the instrument is within specified limits. Panel lamps are provided to indicate when the r„ f. input level is too high or too low. With a suitable input the TF 2304 automatically locks to the carrier signal, the level is automatically set, the meter settles, and a reading can be taken in about five seconds. Measurements can be made, on f.m. transmitters, of both positive and negative deviations at modulation frequencies of 50 Hz to 9 kHz. Eight selectable ranges between 1.5 kHz f,s..d, and 150 kHz f.s.d. are provided. On a.m. transmitters depth measurements up to 95% at modulation frequencies between 50 Hz and 9 kHz can be made at carrier frequencies up to 400 MHz. Peak or trough indication can be selected by a switch. Although measurements are normally made by means of meter readout, i.f. and demodulated outputs are available at the front panel for examination or analysis. A switched de-emphasis facility is provided for the demodulated output to restore a modulation signal that has had preemphasis applied. The instrument can operate from an a„c. mains supply or from an optional rechargeable nickel cadmium battery pack mounted inside the instrument case. The instrument can be operated from the battery pack all day (the continuous operational life of the batterypack is about 8 hours) then charged up overnight using the built-in chargor