INTRODUCTION 1.1 The 9081 and 9082 are synthesized signal generators designed primarily for the testing of radio communications equipment. Although providing the precision of a synthesizer system locked to a high-stability frequency standard they retain the versatility of analogue-type tuning. RF TUNING 1.2 A major feature of the instruments is their 'single-knob' tuning allied to a channelized mode of operation. This enables the instruments to be tuned in steps according to the channel spacing required. The r.f. tuning automatically locks into the centre frequency of the particular channel. Selection of the HOLD position on the front panel switch then electronically disconnects the spin wheel. 1 .3 A fine tune facility provides for interpolation between channels, and this can also be carried out by an external slow sweep voltage if desired. The carrier frequency is displayed on an 8-digit LED readout in which the resolution is varied to suit the particular tuning mode (Fast, Slow or Hold) in use. 1.4 The Channel Spacing switch provides ten different frequency spacings which conform to the internationally agreed requirements of different authorities. A continuous tuning facility (Zf) is provided in which the frequency increments are reduced to a minimum value when using SLOW tune mode. RF OUTPUT 1.5 Automatic levelling maintains the output typically within ±0.5dB over the entire frequency range. A switched attenuator and vernier control provide an output range from -130dBm to +3dBm, (+13dBm for models 9081H and 9082H), calibrated in both dBm and voltage units. An output switch provides a multiply-by-two facility which permits a doubling of the normal output levels in CW, FM and Phase Modulation modes. MODULATION FACILITIES 1.6 AM, FM and Phase Modulation (ζ2Μ) facilities are provided. Three spot modulation frequencies (400Hz, 1kHz and 5kHz) are available from an internal oscillator. External modulation can also be used, the maximum frequencies permitted being 100kHz for FM, 5kHz for $M, 100kHz for AM on Model 9081 and 20kHz for AM on Model 9082. 1.7 The meter indicates both external and internal modulation, and, as these can be applied simultaneously, various arrangements of multiple modulation are feasible (see para 2.4). POWER SUPPLY 1.8 The instruments operate from nominal 110V or 220V a.c. supplies, 45 to 440Hz. Mains voltage selection is by means of two rear panel switches which provide four possible voltage selections and can be locked to the chosen positions by a screwed plate, which allows the selected voltage range markings to be seen. Refer to para. 5.1. HANDBOOK NOTES Frequency Range 1.9 Although the signal generators have a specified operating range extending to 520MHz, the design capability is at least 540MHz. This higher figure with its range subdivisions is used in the technical descriptions except when referring to the actual operating ranges.