1 The Racal Instruments VXlbus microwave counter, Model 2151, is a microprocessor- controlled instrument offering high-accuracy measurements with a comprehensive range of facilities. These facilities include Automatic/Manual Operation, Tracking, Offset, Multiply, and Store and Recall. All the instrument’s functions are controlled remotely via the VXI interface. 2 The Racal Instruments VXlbus UHF counter, Model 2051, offers high accuracy measurement over a reduced frequency range, with a similar range of facilities to those provided on the Model 2151. MEASUREMENT FUNCTIONS Frequency A Function 3 The Frequency A Function is used to measure the frequency of the signal applied to INPUT A. A resolution of up to ten digits can be selected with a gate time of 1 millisecond to 20 seconds depending on the resolution selected. Frequency B Function 4 The Frequency B Function is used to measure the frequency of the signal applied to INPUT B. A resolution of up to ten digits can be selected with a gate time of 1 millisecond to 20 seconds depending on the resolution selected. Frequency C Function (2151 only) 5 The Frequency C Function is used to measure the frequency of the signal applied to INPUT C. A resolution of 0.1 Hz to 1 MHz can be selected with a gate time of 1 millisecond to 10 seconds depending on the resolution selected and frequency being sampled. Ratio C/B Function (2151 only) 6 The Ratio C/B Function is used to measure the ratio of the frequency applied to INPUT C to that applied to INPUT B. Ratio C/A Function (2151 only) 7 The Ratio C/A Function is used to measure the ratio of the frequency applied to INPUT C to that applied to INPUT A. Ratio B/A Function 8 The Ratio B/A Function is used to measure the ratio of the frequency applied to INPUT B to that applied to INPUT A.