Input stage for police radar detector including input signal

Abstract

An input stage for a police radar detector includes a single mixer together with at least one preamplifier to detect radar signals in the X, K and K.sub.a bands. A preamplifier may be used on the X band alone, the K band alone, the K.sub.a band alone, the X and K bands or the X, K and K.sub.a bands. The use of these preamplifiers provides better noise figure; however, multiple responses cannot be scanned at the same time in bands utilizing a preamplifier with sufficient selectivity to reduce noise in its respective image bands to tolerable levels so that some or all of the receiver responses are swept independently with the preamplifier or preamplifiers being enabled one at a time as appropriate for each band being scanned. Since more sweep time is required when multiple responses are no longer swept simultaneously, a currently preferred form of the input stage couples the K.sub.a band signals to a single mixer through a preamplifier which permits multiple responses to be swept in the K.sub.a band, or passively for economy, to receive dual responses in the K.sub.a band. Utilizing a novel frequency scheme for a radar detector yields two responses approximately 1.3 Ghz apart that fall within the K.sub.a band so that the K.sub.a band can be swept by tuning the first LO 124 through a 1.3 Ghz range with the two responses covering the 2.6 Ghz required for sweeping the entire K.sub.a band.