The various signal frequencies are obtained for an incoming carrier centered at 49.86 MHz. The receiver employs double conversion, with i-fs at 10.7 MHz and 455kHz. Ceramic filters are used in both i-fs for selectivity and reduced`coil count. A quadrature detector is used to recover the baseband data, and an integrator and Schmitt trigger are used to filter the demodulated output. Also included is a squelch circuit that functions as a status line, and the open-collector output switches high when a signal is received.
The LM3361A functions as the 2nd LO, 2nd mixer, limiting i-f, quadrature detector, and squelch; yet, it consumes less than 4 mA from a 5-V logic supply. The entire receiver requires approximately 10 mA.