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1.1 FEATURES The TF 144H series of signal generators give c.w. and a.m. outputs suitable for the standard measurements and tests on equipment operating in the m. f. , h. f. , and lower v. h. f. bands. Their good frequency stability and high- discrimination tuning are of particular advantage in testing narrowband communication receivers. Each Generator covers 10 kc/s to 72 Me/ s in twelve ranges. Eight of these ranges follow a straight-line frequency law and have a frequency cover of 2:1; the remaining four have a slightly greater range and one of them covers the medium-wave broadcast band. A large effective scale length is provided on the main tuning dial which has separate hand-calibrated scales for each range. Its discrimination is such that a 2% frequency change on any band occupies more than a quarter of an inch of scale length. Frequency accuracy is ±1%, but for greater accuracy there is a built-in crystal Calibrator which gives at least 90 crystal check points throughout the twelve ranges. An 8: 1 reduction drive from the main tuning control enables easy and precise adjustment to be made, and a linear logging scale with 100 divisions attached to the main tuning control facilitates interpolation between any of the main- scale divisions. In addition to the logging seals, a fine tuning control is provided which is operative above 80 kc/'S and enables incremental frequency adjustments to be made, with complete freedom from backlash, up to ±0. 5% of the frequency in use. Modulation can be applied from an internal 400-c/ s to 1000-c/ s Oscillator or from an external source. In both cases, depth is variable up to 80% over most of the frequency range. There are two r.f. signal outlets. One supplies an output e.m.f. switchable between 2 and 2. 75 volts (monitored by the meter) at very low impedance while the other supplies a variable e.m.f. between 2 (jlV and 2 volts via coarse and fine 50-ohm attenuators; the output range may be extended down to 0.2 [0.V by using the 20-dB Attenuator Pad accessory. A system of automatic level control keeps the carrier level constant throughout wide frequency changes. Designed for operation from either a. c. mains or battery supplies the instrument is available in forms suitable for bench or rack mounting, as detailed below.