Collins 51J-4 Receiver is designed for communication applications where stability and dial accuracy of the highest order are the prime requisites. Under normal operating conditions, the receiver operates in the ,y range of 540 kc to 30. 5 me with a total setting error and drift of less than 1 kc at any frequency within its range. The receiver is designed for amplitude- modulated and continuous wave reception, although its accuracy and stability make it suitable for many applications where it is desired to receive or set definite frequencies without searching or making frequent adjustments. This receiver incorporates the new mechanical filter in the intermediate frequency range to obtain the desirable rectangularshaped passband. 1.1.3. DESCRIPTION. (a) MECHANICAL. - The 51J-4 Receiver is available in two styles. One is a panel and shelf assembly suitable for mounting in a standard rack cabinet. Over-all panel dimensions are: width, 19 inches; height, 10-1/2 inches; and depth behind panel, 13-1/2 inches. A dust cover that fits over the top of the chassis is removable from the rear. The other assembly is in a cabinet suitable for table-mounting. Outside cabinet dimensions are: width, 21-1/8 inches; height, 12-3/8 inches and depth, 13-1/8 inches. Available on special order is a speaker that matches this cabinet. The speaker's dimensions are: width, 13 inches; height, 11 inches; depth, 7 inches. The speaker, the cabinet of the table-mounting assembly, and the front panel of the rack-mounting receiver are finished in St. James Gray wrinkle.