Frequency Calibration via GPS
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Inexpensive Frequency Standard with output synchronized to GPS satellites,
Contents
Features[edit]
- Generates very accurate frequency output
- U-Blox NEO-7M GPS Module
- Remote Amplified GPS Antenna
- FTDI-49MM
- 50 Ohm Output
- Metal enclosure
Parts[edit]
GPS[edit]
- U-Blox NEO-7M GPS Module
- Programmable frequency from USB
- SMA Female connector
- 5V operation (power)
- 3.3V Rx/Tx/PPS levels
U-Center Programming Software[edit]
- TP5 sets PPS output to "any" frequency
- U-Blox website
- Set to 8 MHz on GPS PPS pin when locked
- Other frequencies have some "jitter" but are still GPS accurate
- Set to 2 Hz on GPS PPS pin when not locked
Remote Amplified GPS Antenna[edit]
- 20 dB amplified output
- SMA male connector connects to GPS module without adapter
- Magnetic mount
- Locate outside
FTDI[edit]
- FTDI-49MM USB to serial interface
- U-Center communicates with the GPS over this interface
- Tx/Rx LEDs
- USB signal voltage level jumper set to 3.3V to match Tx/Rx on GPS
- 5V header provides 5V to GPS card
- 49x49mm
50 Ohm Driver (Not Required - nice to have)[edit]
- Used modified PulseGen card to drive 50 Ohms, 5V level output
- Remove oscillator circuit parts (R/C)
- 5 parallel 74AC14 outputs with 249 ohm series resistors on each output
- Able to drive long 50 ohm coax
- Square wave output
- Very fast edges
Case[edit]
- Cabinet Door Bumpers - used as inexpensive rubber feet
Connectors[edit]
- OUT = Frequency source output
- 5V, 50 ohm
- USB
- ANT - external amplified GPS antenna
Calibrating Frequency Counters[edit]
- Two very cheap frequency counters
Videos[edit]
- This is the approach I followed
- GPSDO vs Rubidium Frequency Standard
