Note
QST, Mar 1973, p. 119. (R-4C)
QST, Apr 1975, p. 97.
QST, Apr 1976, p. 103. (extra space for WARC bands)
QST, Dec 1977, p. 152.
The R-4C mirrored the basic appearance of its 4-Line predecessors, but it was a very different receiver. The new triple-conversion model used an 8 kHz wide roofing filter in the first IF at 5645 kHz. The 5695 kHz second IF had a standard 2.4 kHz crystal filter and space for three optional crystal filters ranging in bandwidth from .25-6 kHz. Two L/C circuits in the 50 kHz third IF followed. The pass band tuning had been changed from mechanical to electrical. Additional flexibility was added to the AVC circuit.
References
Adding electronic bandpass tuning. Ham Radio, Oct 1973, 58.
