Remote tuning of NMR probe circuits

There are many circumstances in which the probe tuning adjustments cannot b e located near the rf NMR coil. These may occur in high-temperature NMR, lo w-temperature NMR, and in the use of magnets with small diameter access bor es, We address here circuitry for connecting a fixed-tuned probe circuit by a transmission line to a remotely located tuning network. In particular, t he bandwidth over which the probe may be remotely tuned while keeping the l osses in the transmission line acceptably low is considered. The results sh ow that for all resonant circuit geometries (series, parallel, series-paral lel), overcoupling of the line to the tuned circuit is key to obtaining a l arge tuning bandwidth. At equivalent extents of overcoupling, all resonant circuit geometries have nearly equal remote tuning bandwidths. Particularly for the case of low-loss transmission line, the tuning bandwidth can be ma ny times the tuned circuit's bandwidth, f(o)/Q. (C) 2000 Academic Press.