The NATIONAL TIME GPS Antenna enables the MC100 Master Clock to receive accurate time information from up to 12 satellites. Each satellite sets its time based on the atomic clock at the National Institute of Standards and Technology (NIST) which is exact to milliseconds in ten thousand years. The GPS Antenna sends the number of satellites in view to the MC100 which is displayed on its LCD display. For proper operation, only three satellites are necessary. The communication between the MC100 and antenna is supervised and fault conditions are displayed. During fault conditions, the masters use their internal crystal to keep time accurate. The standard outdoor mounting requires a 1" x 14 TPI pole (by others). The GPS antenna comes standard with a 30' cable. Cable length may be extended to 100' with 5 conductor shielded low capacitance cable. For further distances up to 4000', RS232 to RS485 converters may be used (Telebyte 253T or equivalent) with 4 conductor shielded low capacitance cable.