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Yaesu FR-101

Convert the 3180 kHz IF to 455 kHz . . .

The first part of the circuit is necessary to obtain a 455 kHz IF as the crystal filter in FR-101 is 20 kHz wide. A double balanced mixer IC was chosen for this conversion. A fundamental crystal on 3635 kHz is mixed with the FR-101's 3180 kHz IF. Additional selectivity for the DRM IF is obtained with a Murata CFW455G Ceramic Filter. Terminate the ceramic filter with a 1.5 kohm resistor.

Balanced Mixer

Fig. 1

How to get the 3180 kHz IF from FR-101 . . .

The output from FR-101 is taken from the Noise Blanker FET amplifier at the collector of Q3 on the PB-1252B which is the Mixer and Noise Blanker Printed Circuit Board.

3180 kHz IF Signal Output Point

Fig. 2

Generating a 467 kHz output to the second mixer . . .
The 467 kHz signal source was designed around a 14.944 MHz crystal and a CMOS oscillator. It is the same method as was used for the Yaesu FRG 7700. The 467 kHz output is taken from the divide by 32 output on pin 5. Use a 1 MOhm resistor across the crystal for CMOS Bias.

Crystal Oscillator with a 14060 with Binary Counter

Fig. 3

. . . and the following Balanced Mixer and 12 kHz Output

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.

Balanced Mixer

Fig. 4

The finished Oscillator and Mixer

The finished DRM Oscillator and Mixer

Fig. 5

To the left in the picture the 3635 kHz crystal. The 3180 kHz is fed to the mixer via the coil with the green core. In the middle the Murata CFW455G ceramic filter can be seen. The rest of the circuit is similar to the 12 kHz mixer for the Yaesu FRG 7700.