RF MIXER board does all RX/TX signals on IF and operation frequencies.
On receive the signal comes on CX3 coaxial connector, then passes (or not) through input attenuator R10,R13,R14, then via switches come to BPF board. IF TRAP circuitry consists of L1, C7, C38. Then signal passes through U3 (ERA6SM) RX preamplifier (operator switchable). RX MIXER is on additional subboard and sits over RF MIXER board. 9MHz diplexer follows and then IF amplifier – U12 (ERA6SM). After some switching and attenuation signal comes to the first crystal filter – 2.7kHz then to CX6 coaxial connector and IF/AF board.

On transmit the signal from SSB GEN board through CX7 connector passes through crystal filter and after TX/RX switch to a pin diode D1 attenuator. It is driven by ALC circuitry performed by U16 and T4.
U11 is TX mixer which is fine balanced by R62 and impedance matched by L10,L18 wide band transformers. Output mixed signals are further filtered by BPF board and amplified by U3 and U9. Output attenuator R4,R5,R6 is following then via CX4 signal goes to linear amplifier PA55W board.

Component side PCB

Component side values

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