The EM161 module contains two electronic multiplying networks - each of which needs an operational amplifier of the DA163 module. The multiplier is a parabola multiplier - it uses the identity (a+b)**2-(a-b)**4=4ab, so multiplying two machine variables a and b is reduced to computing two times a power of two function and subtracting the resulting values.

At the end of this operation the result is divided by four by a resistive voltage divider and amplified by an operational amplifier. The two parabola functions are generated by diode function generators which approximate the desired parabola function using secants.

All of the necessary components of the diode function generators are hidden under the metal lid seen in the middle of the photo on the right. This encapsulation is necessary since the diodes of the function generators are temperature stabilized in a small oven maintaining a constant temperature. The oven is heated by a power transistor inside the metal enclosure.

Behind the patch panel