AIP Digital Archive
Electrical Engineering, Measurement and Control Technology
A device is described that provides frequency modulation to the rf signal used in electron nuclear double resonance (ENDOR) spectroscopy. Its use results in excellent spectral (signal) baseline characteristics while allowing a digital frequency synthesizer to be employed as the source of the swept rf signal. The circuit makes use of a surface acoustic wave (SAW) oscillator as the voltage-controlled frequency source of the frequency modulation, as well as rf mixers and a 5th-order Butterworth filter to produce a spectrally clean modulated frequency output. Provision for the input of a second rf frequency for TRIPLE resonance experiments also is provided. The device can be used in any frequency range with good results, as spectra from X- and Q-band ENDOR systems illustrate.
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