An injection and phase-locked super-regenerative NQR spectrometer

Abstract

The details of the design and construction of an injection and phase-locked super-regenerative oscillator (SRO) type NQR spectrometer with signal averaging capabilities and working in the frequency range 15-40 MHz are presented. The injection voltage at the SRO centre frequency f₀ is generated from a carrier-suppressed modulator (CSM) which is used to modulate the output of a variable frequency oscillator VFO at f₁ with that of a fixed frequency oscillator (FFO) at f₂.f₁ is set such that f₀=f₁+f₂ or f₁-f₂. This scheme avoids the problems of leakage radiation leading to uncontrolled injection when one derives the injection signal from a VFO set at f₀. Phase-locking is achieved by phase sensitive detection of the f₂ component obtained by mixing the SRO output at f₀ and the VFO output at f₁ and feeding the DC error voltage to a varactor in the SRO. NQR signals can be obtained by demodulating the f₂ component. A 'lock box' design concept has been adopted so that any oscillator can be phase-locked in principle and resonance signals obtained directly from the 'lock box'. Typical ³⁵Cl NQR spectra recorded with the spectrometer system are presented along with an assessment of its performance.