The Austin EMC frequency standard is now a GPS frequency and time receiver which is more accurate than either the Loran or WWVB system used previously.
A typical calibration includes the following steps:
1. Equipment is temperature stabilized.
2. High accuracy equipment is allowed additional time to reach stabilization.
3. Initial frequency is measured and recorded. This is optionally reported on certificate.
4. An adjustment is made to remove the frequency error.
5. A calibration label is affixed and a calibration certificate is issued.
Direct measurement uses a phase locked HP5345 frequency counter which utilizes a reciprocal technique with a 500 MHz. gate that provides a constant resolution regardless of frequency.
|1 Second||+-4.6X10-9||9 Digits|
|10 Seconds||+-4.6X10-10||10 Digits|
|100 Seconds||+-4.8X10-11||11 Digits|
|1000 Seconds||+-6.6X10-12||12 Digits|
Fractional frequency offset uses the HP5345 to measure the time difference accumulated between two phase locked Frequency Synthesizers set to 100 Mhz. and 100 Mhz plus 1 Hz.with one locked to the house standard, and the other locked to the standard being measured. When both frequencies are equal the time difference will be a constant 10 Nanoseconds which can be measured with a resolution of 2.02 picoseconds in 100 seconds. For signals of 10, 5, and 1 Mhz any offset will be multiplied by a factor of 10, 20, and 100.
Fractional offset time averaged accuracy
|1 Megahertz||5 Megahertz||10 Megahertz|