GPS Frequency Standard

Build V2

Stand-alone design does not require PC. Generates a 10 MHz output after satellite lock.

• NEO-7M GPS
• QTPy49 card
  • CircuitPython code fits into QT Py (SAMD based) but a QT Py (RP2040 based) could be used
  • 3.3V, 48 MHz
• Modified PulseGen card
  • Oscillator circuit removed (not used as pulse generator)
  • Receives input from GPS output and drives 50 Ohm output on BNC
• Status LED
  • Blinks in for 1 second at power up
  • Goes off until serial communications are working
  • Blinks on-off as data is received from GPS while waiting for Satellite signal lock
  • LED is on solid once output is enabled
• Fits into Aluminum Project Box Enclosure DIY 100*76*35mm - ebay search
• Inspired by Scullcom design

Wiring

# Wiring
# Signal   Color  From          To
# GND      Black  QTPy49 J4-1   GPS pin 4
# VCC      Red    QTPy49 J4-2   GPS pin 5
# QTPy>GPS Blue   QTPy49 J4-3   GPS pin 2
# GPS>QTPy White  QTPy49 J4-4   GPS pin 3
# GND      Black  QTPy49 J5-1   PulseGen GND
# VCC      Red    QTPy49 J5-2   PulseGen VCC
# PPS      Purple GPU pin 1     PulseGen In
# LED-VCC  Red    QTPy49 J9-3   D0
# LED-GND  Black  QTPy49 J9-1   GND

Code

• FreqStdCap.ino - tool to generate bytestrings
• GPS_004.py - Final working code
  • Saved as code.py to auto-run
• GPS_003.py - Capture data from GPS module a line at a time - helpful for debugging
• GPS_002.py - Read 32 bytes at a time
• GPS_001.py - Formatted stings output

Build V1

Requires PC running ublox software on PC to set output.

• NEO-7M GPS
• FTDI-49MM card set to 3.3V signal levels
• PulseGen modified to receive output from GPS and drive 50 Ohm output out of the box
• Fits into Aluminum Project Box Enclosure DIY 100*76*35mm - ebay search

GPS

• GPS Satellite Positioning Module NEO7M UBLOX
• Specifications:
• Working Voltage: 3.3v-5.0v
• Color: As Picture Shown
• Description:
• With micro USB interface, you can debug GPS module with ordinary phone data cable, no longer need to use USB-TTL and other tools.
• TTL interface is reserved to facilitate the use of USB-TTL or external microcontroller to control and receive GPS information.
• Ceramic antenna on module board, no GPS external antenna can be used to search for stars.
• Reserved SMA antenna interface, can use external antenna, star search ability is stronger.

Reference Materials

• Design & Build a GPS locked Frequency Standard- Scullcom
• SIMPLE 10 MHZ GPS FREQUENCY STANDARD AND RF GENERATOR
  • uses Arduino Nano as FTDI replacement
• An Arduino-based GPS Disciplined Oscillator
• An Arduino Version of Brooks Shera's GPSDO
• Simulating the Brooks Shera (W5OJM) GPSDO Algorithm