PSK transceiver circuit

The transmitter uses another SA612 (U6) for mixing the BFO oscillator with a 9 MHz VXO signal produced by the SA612. The VXO uses two crystals in parallel for increased range, along with a series inductor. The frequency is voltage tuned using a 10 turn pot and 1N4756 Zener didoe used as a tuning diode, which gives enough capacitance swing to tune the VXO about 1.5 kHz, using HC-49US crystals. This tuning range matches the band width of the receiver's crystal filter pretty closely.

The transmitter mixer output is filtered by a double tuned circuit, using modified 10.7 MHz IF cans. The modification is simply breaking out the cap in the bottom of the can, so it can be retuned to 14 MHz using an external cap. A two stage transistor amp (Q4, Q6) brings the signal level up enough to drive the gate of a 74HC86 XOR gate (U4). The XOR gate is used to change the phase of the transmitted signal and to drive the gates of the three BS170 MOSFETs used for the power amplifier. Two gates are connected in parallel to improve drive to the PA gates.