Does this coding look familiar to anyone? RC transmitter

The "carrier" waveform is a square wave at 14Hz. The embedded coded waveform is a variable pulse width square wave running at 300Hz.

 

The transmitter in this case is from a Chamberlain (Sears) garage door opener from around 1980. When a signal was sent from this transmitter, what I found on the receiver board was a little "burp" on the output of the op-amp that resided on the receiver board. The output voltage would stutter for about a half second then jump to 1.5 volt above its quiescence level for another half second. This was enough of a signal to condition and update the logic circuit in the gate opener unit that I constructed. I am still curious as to what the "official" signal was out of the receiver circuit and how it was differentiated from the other possible 143 signals.

 

I did take some IC numbers from what appeared to be a Tx and Rx set. One each located on their respective board. I think it was the Tx component data sheet that I found, or it may have merely a chip for sale. A little vague on the memory.