Remote frequency calibrations :

Abstract

The FMAS is a network of individual frequency measurement systems located at each of its customer's laboratories, and connected by telephone lines to the NIST laboratories in Boulder, Colorado. Each individual system includes a GPS satellite receiver and antenna, a time interval counter, and a computer that controls the measurements. The data collected from all customer sites are stored and archived at NIST, and calibration reports are sent each month to every customer. Several master units are also maintained by NIST. The master units, which comprise the same hardware and software as the customer's units, continuously compare the received GPS signals to the national frequency standard. In this way, NIST can continuously monitor the frequency uncertainty of each customer's unit, and the uncertainty of their primary frequency standard. This chapter begins by providing a history of the FMAS. It then provides a physical description of the FMAS components and facilities. Remote Frequency Calibrations: The NIST Frequency Measurement and Analysis Service Item Description Solid State Flash Memory Disk megabyte or higher capacity with embedded ROM-DOS operating system. Measurement software is preinstalled. Video Card Compatible with minimum requirements of VGA standard, 640 × 480 resolution, 16 colors. Modem 14.4 kilobit per second modem (V.32 standard), compatible with existing software. Time Interval Counter Custom designed counter with 8-channel multiplexer, 24-bit frequency dividers, 30 ps resolution. Accepts 1, 5, or 10 MHz external time base signal, provides RS-232 interface for GPS receiver [16]. GPS Receiver Motorola Oncore 8-channel parallel tracking GPS receiver (mounts on time interval counter card). GPS Antenna Active GPS antenna with > 30 dB gain, mounting hardware, and cable. The cable is made to customer's specification. Total signal loss on cable should not exceed 20 dB for the GPS L1 carrier frequency of 1575.42 MHz. Various types of coaxial cable are used to meet this requirement. Uninterruptible Power Supply (UPS) 500 VA supply with four AC outlets. BNC Cables BNC to BNC cables provided for all 5 measurement channels.