You may say "But nyquist says you can't transmit or receive frequencies at more than 1/2 the sample rate (40 MHz in this case). To a degree that is true. Some people thought it may be overtones, but what happens in reality something stranger happens. Everything you transmit is actually mirrored around 1/2 the sample rate (40 MHz). So, transmitting 60 MHz on an 80 MHz bitclock creates a waveform both at 60 as well as 20. This isn't perfect. Some frequencies line up to the 80 MHz well, others do not. We store a bit pattern in the "premodulated_table" array. This contains bitstreams for various signals, such as the "sync" level or "colorbust" level, or any of the visual colors. This table's length of 1408 bits per color was chosen so that when sent out one bit at a time at 80 MHz, it works out to an even multiplier of the NTCS chroma frequency of 315.0/88.0 MHz, or 3.579545455 MHz. You can calculate this by taking 1408/80MHz = 17.6us * 3.579545 MHz = 63 cycles, exactly. Conveniently, it also works out to an even multiplier of 61.25 MHz, Channel 3's luma center. 17.6us * 61.25 MHz = 1078 cycles, exactly! When you modulate arbitrary frequencies, sometimes the cycles come out very uneven.