3-1-4 RF AMPLIFIER AND 1ST MIXER CIRCUITS(RF UNIT)The 1st mixer circuit mixes the receive signals with the 1stLO signal to convert the receive signal frequencies into a64.455 MHz 1st IF signal. The IC-756PRO has two 1st mixercircuits for the dualwatch function.The signals from the pre-amplifier circuit, or signals whichbypass the pre-amplifiers, are divided at L491. Each signalis applied to a 60 MHz cut-off low-pass filter, RF amplifier(Q501, Q601) and then to a 1st mixer (Q511–Q514 orQ611–Q614).Each 1st LO signal (64.4850–124.4550 MHz) enters the RFunit from the PLL unit via J561 or J661. The LO signals areamplified at the LO amplifier (Q561 or Q661), filtered by alow-pass filter, and then applied to each 1st mixer.