Fixed-coil display system for data extraction

The development of data handling systems has demanded a rapid and accurate means of extracting radar data from p.p.i. displays. Possible systems include the use of mechanical aids, such as pantographs, and of electronically produced markers on the p.p.i. display which are capable of being positioned independently of the radar data. A fixed-coil display system using the latter method is described. The system uses a centrally generated linear time-base which is resolved into sine and cosine components to produce the trace on a display in the direction of look of the aerial system. Each display console can accept two voltage inputs in each of the orthogonal co-ordinates, and a diode clamp switch is used to feed each in turn to the deflection amplifier and coils. These inputs normally accept the time-base and inter-trace marker input. To obtain accurate registration between the marks produced on the cathode-ray-tube face by equal voltages fed to the two inputs, d.c. level setting and gain equalization are needed. As an example of the use of the display system, the tracker´s display of an experimental data extraction system is described. One of the most intractable problems met was ?spot wander?. This name is given to the effect where an inter-trace marker, positioned by steady deflection voltages, moves in position on the cathode-ray tube in sympathy with the deflection waveform fed to the other input of the console. Several causes were discovered and the effect was reduced to acceptable levels. Further development work to improve the accuracy of the system has been carried out. To achieve accuracy of registration an automatic zero control system is used, and an overall stability of registration at zero voltage of 1 part in 5000 has been obtained. A secondary source of error was in the non-linearity of the magslip resolver circuit. This was of the order of 1 part in 1000. However, by means of certain circuit improvements a linearity through the resolver of about 1 part- - in 5000 has been achieved.