Radio is such a rabbit hole. I fiddled with the GAL based RCDR (R-C Defined Radio) for a few weeks, learning, sometimes re-learning, interesting things along the way. Since the GAL could not directly switch the antenna signal, it seemed to be overkill for a simple receiver. So, I rebuilt the receiver with just TTL devices, a pair of XOR gates for the oscillator and a 7476 J-K flip-flop for the quadrature divider. I still used the 4066 switch, but it was soon replaced with MOSFETs and later, diodes. Still, the circuit looked excessive for the task.

The first thing to go was the decoding and processing of the quadrature signal, it is not needed for the CW signal. That means that there is one less op-amp and half as many switches/MOSFETs/diodes needed. A good start. Hold on, op-amps can oscillate, do I really need the XORs? Nope, they are gone. One less chip!

Since the Q signal is no longer being used, do we really need to generate it? Nope. That removes the divide by four, so no more flip-flops. All that remains is a dual op-amp and switch chip. Sayonara switches, you are diodes now. The op-amp is the last chip standing. We have a winner!

If a dual op-amp is all that is needed to form the core of a receiver, what could another pair of op-amps, from the quad package version, bring to the party?

Here is where the receiver stands presently:

• 0 inductors (Sometimes 1, I still have the ethernet cable loop antenna)
• 0 special or high performance parts (are op-amps from the 1990s special?)
• 1 generic transistor (2N3904)
• 2 generic diodes (1N4148)
• 4 op-amps (TL074B )

If you would like to try this at home, adjust R1, R2, R3 so that the voltage across R6 is near 0VDC. Next is to adjust R9 and C4 until the square-ish wave at pin 7 is about 57kHz. If you want to listen in, add an output coupling capacitor, plug in to your sound card and start up Quisk. (Update: Things will work better when R6 connects to -5V rather than gnd.)