Bidirectional frequency conversion circuit

Shown is a bidirectional frequency conversion circuit . In the receiving state (RX), the signal received by the antenna enters the band-pass filter (BPF), and
the signal is added to the source (s) of the field effect transistor VT1 through the filter. The local oscillator signal is added to the gate of VT1, and the drain (D) of VT1 is connected to the primary winding of the intermediate frequency transformer. The primary winding of the intermediate
frequency transformer Tl resonates with the parallel capacitor at the intermediate frequency frequency. It outputs the difference signal after VTL mixing
. In the receiving state, the control terminal causes VD2 to be forward-biased and conductive, and the intermediate frequency signal is output through VD2, and then output through the transistor filter and the bidirectional
intermediate frequency amplifier .
    When sending a signal, the control terminal is ov, VD1 is turned on, and the intermediate frequency signal is added to the winding of the intermediate frequency transformer through the amplifier, crystal filter and VD1. The path of the local oscillator signal remains unchanged. The signal is input from the drain of VT1, and the source (s) output is then sent to the antenna
through the bandpass filter and transmit amplifier (TX) to transmit the signal.