GPS Locked 10Mhz Frequency Reference
This project came about because of a need to accurately calibrate the piles of HP test equipment I have been buying off ebay. This project uses a 10mhz voltage tuned crystal oscillator whose frequency is locked to the GPS positioning system clock. The GPS I used was a Canadian Marconi (CMC) Superstar single board OEM GPS receiver with a Motorola external amplified GPS antenna. The ovenized crystal oscillator is a modified Anritsu MH4100A standard crystal oscillator. These parts are not something you may be able to easily source, but the concept can be used with other devices. The superstar GPS has status block that is transmitted serially that contains an estimate of the GPS internal 10mhz oscillator frequency error. I replaced the internal 10mhz clock on the GPS card with the ovenized voltage tuned 10mhz crystal oscillator. By using a PIC microcontroller to read the serial error word transmitted from the GPS card, and having the PIC output an analog tuning voltage to the 10mhz oscillator, I was able to lock my oscillator to the GPS clock system. Typical reported errors in the 10mhz signal when locked are in the range of 10e-11hz to 10e-12hz.
- A voltage tunable 10mhz crystal oscillator.
- A GPS card that outputs a detailed status message relating to its clock error
- An external GPS antenna for the GPS card
- A little hardware and software magic to tie them together
Autocad drawing file - 10mhzgps.dwg(37.9K)
Postscript of Drawing - 10mhz.ps(252.4K)
PIC assembler source code - f627-10mhz.asm(21.5K)
All project files (source, dwg, listing etc) in linux compressed tar format - f627-10mhz-may16-src.tgz(31.7K)
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