The pulse-testing of wide-band networks

A description is given of a pulse-testing equipment for wide-band networks, together with examples of practical applications. The equipment contains a pulse generator, a time base with a display unit, and an amplifier preceded by an exploring probe-head. The pulse generator produces three types of pulse: one of length 0.02 microsec and amplitude 35 volts in a cable of 35 ohms; one of length 0.01 micro-sec and small amplitude; and one of amplitude variable from 50 microvolts to 0.5 volt. The time base produces a slow scan and a fast scan (5.0 microsec and 1.0 microsec sweep respectively). A phase shifter provides a continuous adjustment of the position of the pulse response along the trace. The main features of the amplifier are its wide band (32 Mc/s), its high gain (13.5 db per stage) and the adjustable capacitance attenuator in the probe head, which permits of the very low input capacitance of 1.8 ¿¿F at maximum attenuation. The equipment is specially designed for the pulse testing of wide-band networks. The shape of the pulse response gives a great deal of information on the characteristics of the networks, which can usually be obtained only by laborious attenuation and phase measurements. Some typical examples are given: (a)Testing of lines and feeders; study of irregularities in cables and correct matching. (b)Testing of delay lines. (c)Testing of band-pass filters and relations between the pulse response and mismatch. (d)Testing of aerials and mismatching between feeders and aerials. (e)Study of feedback amplifiers. It is shown that the shape of the pulse response gives information on the degree of stability of the amplifier and on the frequency at which it may oscillate. This application is a typical example of the versatility of the pulse-testing technique.