Model BWD 539D is a portable dual trace oscilloscope providing a measurement capability that is unique in an instrument of its class. The identical vertical amplifiers have a -3db response >25MHz and are useful for signal monitoring to beyond 30MHz. Stable triggering extending to > 30MHz makes the BWD 539D suitable for use with 27MHz C.B. and radio control gear. The two vertical amplifiers may be cascaded for a single channel display over a bandwidth of 12Hz to 100kHz at a sensitivity of 0.5mV/cm. The time base and trigger facilities complement the vertical amplifier performance with a sweep range from lOOnSec/cm to 2.5sec/cm whilst waveforms can be triggered from 2Hz to over 20MHz and presented with complete stability. Video displays are well catered for with an active sync separator supplying frame or line pulses for stable lock even if the signal is almost lost in noise. Additional versatility is provided by the sync separator as it also operates as an AM demodulator enabling double or single sideband displays to be locked to the modulation envelope. Identical X-Y operation is also incorporated in the 539D and is phase corrected from DC to over 200kHz enabling accurate phase measurements to be made over this range. Applications requiring accurate phase measurements to power line operated equipment can be readily made on a BWD 539D as it incorporates a zero crossover reference waveform in the calibrator output. When this waveform is used to provide external trigger for the time base, the start of the trace will be within 2° of the power line 0° or 180° cross over points. Thus firing angles of thyristors or triacs can be measured to within 2 or 3°. Application notes relating to all the oscilloscopes facilities are contained in Section 6 and 7. To ensure a long and trouble free life certain precautions should always be observed with electronic instruments. If it is left standing for long periods or is used in a dusty atmosphere keep the instrument covered with a plastic dust cove'r or in a cupboard. Although this instrument has been designed for reliable long term use and has been subject to environmental tests and heat soaked, it is always advisable to store it away from heat or out of direct intense sunlight to minimise temperature cycling of components and possible premature drying out of electrolytic capacitors. Internal temperature rise of the 539D is low but care should still be taken to ensure that the cabinet has adequate ventilation.