EXTREMELY FAST RECOVERY-TIME RECEIVER FOR PULSED NMR

A radio-frequency receiver-amplifier for pulsed nuclear magnetic resonance applications is described. This amplifier has a voltage gain of 2000 and a bandwidth of 5-115 MHz and consists of three identical stages having nonsaturating overload characteristics. Each individual stage recovers within a time of 1 nsec following a 20 dBm overload. The blocking effect of capacitive interstage coupling following rf pulses has been essentially eliminated using series-tuned broad bandwidth resonant circuits between circuits. Measured receiver recovery times range from 250 nsec for short (400 nsec) transmitter pulses to 2. 0 mu sec for long (75 mu sec) pulses. The effective receiver input noise voltage measured following phase-sensitive detection and at the output of a video amplifier having a bandwidth of 320 kHz was 1. 2 mu V.