|The 467 kHz output from the CMOS oscillator / divider is fed via a small capacitor to an IF Transformer tuned to the oscillator frequency and fed to one of the the balanced mixer's inputs, pins 11 and 13. The IF is fed from the Murata 455 kHz filter in Fig. 1. The IF voltage level at this point is about + ? dB µV. |
A second 455 kHz IF transformer feeds the 455 kHz IF to the balanced input to the S042P on the pins 7 and 8. The 12 kHz IF output is recovered on pin 2. The isolation between the receiver and the PC is again provided by the interstage transformer found in an old CB transceiver. To further increase the bandwidth of the IF signal, a 6,8 kOhm resistar is soldered in parallel to the primary winding of the transformer. A small ceramic capacitor is soldered to the secondary winding of the transformer.
The S042P provides ample 12 kHz output to feed the Line Input of the computer's Sound Card. Be sure to mute the Line Input in the computer's Volume Control Panel, otherwise the 12 kHz signal will be heard in the speakers.
If you connect to the computer's Microphone Input, then it would be wise to add a 5 kOhm potentiometer to the secondary winding of the transformer.