Originally Posted by howardcano

That's almost correct!

The method is called Binary Phase Shift Keying (BPSK). There are many descriptions of it on the internet, but here's a quick description particular to the example you gave:

A logic 1 is indicated by ANY reversal in the carrier phase. (This is just a convention I am using. We could just as easily say that the carrier reversal indicates a logic 0.) The initial carrier phase, before data is sent, is unimportant.

First, the data stream must be preceded for a short time with the carrier turned on to give the tank circuit time to "ring up" to full amplitude, and time for the phase detector in the decoder to generate a first valid output. Then a start bit (an initial logic "1") is sent to indicate the beginning of the data stream.

So the sequence is:

1. pin 5 = low, pin 6 = low, tank circuit is not not driven and does not radiate.

2. pin 5 = high, pin 6 = low, initial ring up for tank circuit

3. pin 5 = low, pin 6 = high for one machine cycle (4 carrier periods) sends the start bit

4. No changes for 3 more machine cycles (12 carrier periods) sends "000"

5. pin 5 = high, pin 6 = low for one machine cycle (4 carrier periods) sends a logic "1"

6. No changes for 3 more machine cycles (12 carrier periods) sends "000"