High-frequency oscillating magnetic field

The radio frequency pulse is a very short (tens of microseconds), and a very high power (tens or hundreds of watts) pulse of radio frequency power applied to the probe coil at or very near the Larmor frequency. It has a rectangular envelope the power turns on and instantly reaches full power, then at the end of its duration it goes instantly to zero. The pulse creates an oscillating magnetic field, which can be represented by a vector (the Z i vector ) that rotates in the x-y plane at the frequency of the pulse. The length of the B vector is equal to the amplitude of the radio frequency pulse. 

Figure 3.7 Schematic diagram of a phase-sensitive detector at 20 MHz. The transformer is replaced by an active circuit in the HP8709A synchroniser, and probably most high precision configurations. The phase error voltage output is amplified and used in the spectrometer to control the YIG oscillator magnetic field and hence lock the YIG source frequency to the synthesiser frequency. An identical device locks the Gunn MMW source to the YIG frequency (Adapted from Connor )...

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