Fig 5 Audio 1477-Hz generator. This is identical to Fig 5 in note 2. The LPCLK output is not used in this receiver.

provide 50-£2 local-oscillator signals to the SBL-1 mixers on the R1 boards.

The asymmetrical Q output from the third flip-flop, has less fundamental-frequency component than has the symmetrical I output from the fourth flip-flop. This results in the SBL-1 in the Q-channel R1 board having more conversion loss than the SBL-1 in the I-channel R1 board. The Q-channel R1 board has higher gain in the U2B stage to compensate for the added conversion loss.

The two R1 boards of Fig 6 use KK7B's 1000-Hz seventh-order elliptical low-pass filters. The two boards have their 500-12 volume controls ganged together

I could not obtain a dual 500-ii control, so I used a Radio Shack dual 100-kil control, with a 500-fi resistor across each section.

The audio power stages of the R1 boards, Q5 through Q9, are omitted, and R21 is connected directly to U2B's output (U2 pin 5). The values of R20 and R21 are increased to provide more gain. These values are larger on the Q board to provide the higher gain mentioned above.

Capacitors C30 and C31 ac-couple the R1 audio outputs to the audio mixers, U8 and U9, to eliminate the effects of dc offsets in U2 on the R1 boards. Germanium diodes D31, D32, D33, and

D34 protect CMOS mixers U8 and U9 from voltage transients as power is turned on and off.

The clock generator of Fig 5 is identical to Fig 5 in my exciter article (note 2). This circuitry generates the 1477-Hz audio carriers for audio mixers U8 and U9 (Fig 6).

IC1 and ICO comprise a two-bit digital local-oscillator signal to double-balanced mixer U8. QC1 and QCO go to double-balanced mixer U9. These are two-bit signals rather than square waves, so the outputs of U8 and U9 will lack frequency components at the second, third, or fourth harmonics of the 1477-Hz audio carriers mixing with the

1 /2 W

Fig 6—31 boards, audio mixers, and audio stage of the receiver. The two R1 boards are wired for different gains to compensate for the different duty cycles of the I and Q outputs of the local oscillator generator.

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