The TF 1066b/6 and TF 1066B/6R Signal Generators give s.w., f.m. and a.m. outputs and are intended for making standard measurements and tests on apparatus operating in the v.h.f. and u.h.f. bands. Apart from the normal applications for f.m. receivers, they are particularly suitable for testing multi-channel telemetry equipment requiring a signal source which provides high modulating frequencies and wide deviations with low distortion. A frequency coverage of 10 Mc/s to 470 Mc/s is provided in five ranges. The clear hand-calibrated tuning scale permits precise frequency setting but, for greater accuracy, a crystal calibrator is incorporated with marker pips available at 1 Mc/s intervals. Calibrated incremental frequency shifts may be made; either in preset steps or by using the continuously variable control. In each case the amount of shift is indicated by a meter. F.M. deviations up to 400 kc/s (depending on the carrier range) can be obtained. Two internal modulation frequencies may be selected and the wide frequency response of the modulator permits the use of high frequency external modulating sources. Either internal or external amplitude modulation can be produced to a depth of at least 40%. Accurate monitoring facilities are provided for each type of modulation. The r.f. output level of the Signal Generator is controlled by a constant impedance piston-attenuator. The attenuator dial is direct reading in terms of source e.m.f. or voltage developed across a 50 Ω load. There are two versions of this Signal Generator; TF 10ббB/б, intended for bench mounting and TF 1066B/6R, suitable for mounting in a 19 inch rack.