Extremely fast recovery time receiver for pulsed NMR

Abstract
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 stages. Measured receiver recovery times range from 250 nsec for short (400 nsec) transmitter pulses to 2.0 μsec for long (75 μsec) 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 μV.

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