Difference between revisions of "Frequency Calibration via GPS"

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Inexpensive Frequency Standard with output synchronized to GPS satellites,
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Inexpensive Frequency Standard with output synchronized to GPS satellites.
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[[http://land-boards.com/blwiki/index.php?title=GPS_Frequency_Standard|Version 2 build is here]]
  
 
[[File:FreqSrc-Front-01-720px.jpg]]
 
[[File:FreqSrc-Front-01-720px.jpg]]

Revision as of 16:47, 3 July 2022

Inexpensive Frequency Standard with output synchronized to GPS satellites.

[2 build is here]

FreqSrc-Front-01-720px.jpg

Features

  • Generates very accurate frequency output
  • U-Blox NEO-7M GPS Module
  • Remote Amplified GPS Antenna
  • FTDI-49MM
  • 50 Ohm Output
  • Metal enclosure

Parts

GPS

  • U-Blox NEO-7M GPS Module
    • Programmable frequency from USB
  • SMA Female connector
  • 5V operation (power)
  • 3.3V Rx/Tx/PPS levels

NEO-7M-02.PNG

NEO-7M-04.PNG

NEO-7M-05.PNG

U-Center Programming Software

  • 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

U-center-10MHz.PNG

Remote Amplified GPS Antenna

  • 20 dB amplified output
  • SMA male connector connects to GPS module without adapter
  • Magnetic mount
  • Locate outside

GPS Antenna.jpg

FTDI

  • 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

FTDI-P1746-CROPPED-720PX.jpg

50 Ohm Driver (Not Required - nice to have)

  • 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

PulseGen Mod P18338-720px.jpg

Case

FreqSrc-Top-01-720px.jpg

FreqSrc-Back-01-720px.jpg

Connectors

  • OUT = Frequency source output
    • 5V, 50 ohm
  • USB
  • ANT - external amplified GPS antenna

Calibrating Frequency Counters

  • Two very cheap frequency counters

FreqSrc-Counter-01-720px.jpg

Videos

  • This is the approach I followed

  • GPSDO vs Rubidium Frequency Standard