For this log entry, I was planning to write about using a GAL and an op-amp to create the WWVB receiver with just two chips. Not quite, it turns out the inputs of the GAL are buffered to permit an input singal to be used throughout the device while appearing as a single TTL load to the outside world.

With that plan out the window, a new one was devised. Configure one cell as a buffer and another as an inverter. These two cells are used to create a resistor-capacitor fixed frequency oscillator. Adjust R1, R2 and C to oscillate at four times the frequency that we are interested in. For WWVB that would be 240kHz, easy peasy. (See Stupid PLD Tricks later in the project logs.) Next up, use two more cells to create a two bit Johnson counter or, if you look at it sideways, it becomes a quadrature clock divider. Do you see where we are going now? If not, here are a couple of relevant Hack-A-Day articles:

https://hackaday.com/2024/03/19/breadboard-sdr-doesnt-need-much/

https://hackaday.com/2021/04/19/a-superheterodyne-receiver-with-a-74xx-twist/#comment-6341125

The remaining cells are decoded I and Q signals, with a handy active high/active low Mode selector. Formatted for GALasm, it looks like this:

BufOut =  BufIn;
InvOut = /InvIn;
I.R = /Q;
Q.R = I;
Y0 = I * Q * Mode + /I * /Mode + /Q * /Mode;
Y1 = /I * Q * Mode + I * /Mode + /Q * /Mode;
Y2 = /I * /Q * Mode + I * /Mode + Q * /Mode;
Y3 = I * /Q * Mode + /I * /Mode + Q * /Mode;

Once things were programmed, connected, powered and a suitable RC was selected, I was rewarded with beeping. Digital chips can make a receiver. Far out!