A Miniature Tuned Reed Selector of High Sensitivity and Stability

Tuned reed selectors used as selective receivers in multifrequency systems involving large numbers of individual selections, such as personal radio signaling,1 must operate within close and specifiable limits in order to avoid false signaling and to assure satisfactory performance under devious environmental and circuit conditions. In particular, three operating characteristics, or their equivalents, must be controlled, namely: the resonant frequency, the sensitivity (current or power needed at the most sensitive frequency), and the bandwidth (the frequency band in which contacting occurs with an input power twice that needed at the most sensitive frequency). The permissible variation in these characteristics is much smaller than would seem necessary from first considerations. Resonant frequency changes that seem negligible compared to the frequency spacing between adjacent selectors often become important when other system requirements are considered simultaneously. For example, the frequency range over which contacting will occur depends upon the electrical input level and the selector bandwidth. Consequently, feasible limits for both of these latter quantities must be considered, and in determining allowable frequency deviations from nominal, the lowest probable input level and 411