The TrueTime GPS receiver and frequency standard I have puts out IRIG-B as well as 4 each 10 Mhz. signals. What in practical terms is the IRIG-B (AM, not DC) good for? Al, K9SI > The DC code was usually TTL compatible PWM and the IRIG-B would be 3V > pk-pk AM. Marker 8 cycles, "1" 5 cycles and "0" 2 cycles wide. Spaces 1V > pk-pk.