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The balanced modulation circuit used for SSB generators is an old IC, and there are general-purpose ICs such as MC1496, uPC1037H, and AN612, which are sufficient, but I used to use them often. When building your own, the overall level distribution is an audio signal up to the modulator, and the level of this area must be managed at a small level with the above ICs. I always have to be very careful about the S/N ratio, which is a bit difficult to do, and it is also difficult to obtain because it is only available in market stock. The modulation circuit used in my current homemade machine is an analog switch, and even if the input signal (modulation signal) is input at 2Vpp, the intermodulation distortion can be secured at -70dB, so it is easy to design. The following is the balanced modulation circuit of the TX-Neptune.


Schematic File
This circuit generates harmonics at the output because the modulated signal is completely switched by the carrier wave with an analog switch. Therefore, this type must have a filter (LPF or BPF) in the output circuit to remove harmonics. The AD8402 is the hand and foot circuit for ACN operation. If you want to ignore the ACN circuit, replace the AD8402 and connect the 471 fixed resistors from +5V to R10 and R11 respectively.
ƒAdjustment„
‡@@With the input signal OFF, adjust VR3 and VR4 alternately so that carrier leakage at the OUT terminal is minimized.
‡A@Input an input signal (modulation signal) of 1 Vpp and alternately adjust VR1 and VR2 so that the opposite side signal at the OUT terminal is minimized.
Even if you adjust the reverse side suppression to the best, the value will deteriorate due to temperature dependency. As a method to minimize this, it is possible to insert a thermistor into the R8 or R9 line to correct it. Since the temperature polarity of the thermistor is fixed, check which temperature polarity the system has and decide whether to use R8 or R9. However, you need to repeatedly check and determine the damping resistance of the thermistor to extract the optimal temperature gradient. This is a task for people who are particular about their work.
The SSB (LSB/USB) signal is generated by adding or subtracting the modulation signal from the U column signal and the modulation signal from the L column signal at the 74HC4053 output.


Output waveform (before the filter)
 Output waveform (after filter)
Output: 2T signal J1/J2 carrier waveform