| 摘要 |
Tuning of an RF probe (10) by comparison with a 50 ohm terminator. A Fourier transform NMR spectrometer is used in the comparison operation. The spectrometer comprises an oscillator (30) modulated by a modulator (32) and a signal is directed through duplexer (34) to a probe (10). The signal output of the probe presented to duplexer (34) is directed to an RF amplifier (38). Phase sensitive detector (40) operates on a reference phase derived from the RF oscillator (30) and the RF amplifier output signal to resolve the RF amplifier signal into phase quadrature components by incorporating two phase detectors fed with reference signals at the same frequency but differing in phase by 90<o>. For a signal frequency exactly equal to the reference frequency, the quadrature detection method provides independent determination of two quadrature components of the signal. Analog to digital conversion (42) operates on the phase sensitive detector outputs and the digital signals are available for further processing by processor apparatus (44). The present timing procedure measures two parameters, phase and amplitude, rather than the single parameter techniques of prior art such as signal peaking, reflected wave nulling and the like. The two channels of the quadrature resolving receiver are ideally suited for processing of the relevant information and storage in the spectrometer memory. During operation according to the present invention on the modulator (32) may be considered bypassed in the operational sense. The RF carrier is applied through the duplexer to the probe (10) or a probe substitute in the preferred form of a standard 50 ohm termination. |
