FEATURES The TF 2002B gives high quality a. m. outputs from 10 kHz to 88 MHz and f. m. outputs between 100 kHz and 88 MHz. It has very high frequency discrimination which, coupled with the good stability reached soon after switching on, makes it particularly suitable for setting up and adjusting crystal controlled receivers where the channel spacing is small and the i. f. pass band must have an accurate absolute setting. Another feature is the low leakage which will be found of advantage for tests on receivers that have an internal ferrite rod aerial. Permeability tuning of the oscillator and output filter modules enables the complete range to be covered in only eight bands. The hand calibrated near- logarithmic tuning scale is displayed in a continuous zig-zag pattern, with scales running alternately left and right. This cuts out much of the tedium usually associated with tuning about the band-change frequencies. Above 100 kHz (carrier frequency) direct reading incremental tuning gives high discrimination. Frequency control can also be achieved by externally applied d. c. or by the use of Digital Synchronizer TF 2170B. Crystal check points are available at intervals of 1 MHz, 100 kHz or 10 kHz. Subsidiary check points can be switched in at 1 kHz relative to each of the main points. The dial of the incremental control can be adjusted to high accuracy against the crystal check points by means of two independent trimmer controls. Up to 1 V p. d. can be obtained with 100% modulation over all the range and up to 2 V p. d. is available with c. w. or f. m. outputs. Output is controlled by cam operated 20 dB and 1 dB step attenuators with voltage and dB calibration in terms of p. d. across a 50 Î2 load or of source e. m. f. ; interpolation between attenuator steps is provided by the carrier level control and meter. Automatic level control holds the output constant against frequency or range changing. An auxiliary unmodulated output is available for driving a counter or the Digital Synchronizer TF 2170B. Internal a. m. up to 100% is produced by a continuously tuned low distortion oscillator covering a frequency range 20 Hz to 20 kHz. This means that the generator can be used for r. f., i. f. and a. f. response measurements on a receiver with no additional equipment other than a receiver output meter. The oscillator output is available for external use at terminals situated at the rear of the instrument. Envelope negative feedback ensures a good modulation quality up to at least 80%, and modulation depth is independent of both carrier tuning and carrier level. The continuously variable a.f. oscillator also provides frequency modulation, and deviation is indicated directly on the modulation meter. Three ranges of deviation are provided for each carrier range above 200 kHz. External frequency control terminals can be used to provide dynamic sweep measurements (with or without internal AM), FSK, phase modulation or digital f. m. External amplitude control terminals can be used for level control programming or modulation at a very low frequency without phase shift. Silicon devices are used throughout and emphasis has been placed on accessibility despite the compact structure and thorough screening. The instrument has three major horizontal sections; the centre one containing the oscillators and other circuits can be withdrawn and operated without electrical disconnection.