Difference between revisions of "Frequency Calibration via GPS"

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−
8 Mhz Output synchronized to GPS satellites
+
Inexpensive Frequency Standard with output synchronized to GPS satellites - requires PC connection.
 +
 
 +
[[GPS_Frequency_Standard|Version 2 build is here]] - does not require PC connection
 +
 
 +
[[File:FreqSrc-Front-01-720px.jpg]]
  
 
== Features ==
 
== Features ==
  
 +
* Generates very accurate frequency output
 
* U-Blox NEO-7M GPS Module
 
* U-Blox NEO-7M GPS Module
 
* Remote Amplified GPS Antenna
 
* Remote Amplified GPS Antenna
−
** SMA Male connector
 
 
* [[FTDI-49MM]]
 
* [[FTDI-49MM]]
−
** Used to program the GPS module
+
* 50 Ohm Output
−
* [[PulseGen|Pulse Generator]] modified to provide 50 Ohms, 5V drive
+
* Metal enclosure
−
* Mini-360 Switching Power Supply
 
−
* 5V out
 
−
** 7-23V in
 
  
 
== Parts ==
 
== Parts ==
  
 
=== GPS ===
 
=== GPS ===
 +
 +
* U-Blox NEO-7M GPS Module
 +
** Programmable frequency from USB
 +
* SMA Female connector
 +
* 5V operation (power)
 +
* 3.3V Rx/Tx/PPS levels
  
 
[[File:NEO-7M-02.PNG]]
 
[[File:NEO-7M-02.PNG]]
Line 22: Line 29:
  
 
[[File:NEO-7M-05.PNG]]
 
[[File:NEO-7M-05.PNG]]
−
 
−
* U-Blox NEO-7M GPS Module
 
−
* SMA Female connector
 
  
 
==== U-Center Programming Software ====
 
==== U-Center Programming Software ====
  
 +
* TP5 sets PPS output to "any" frequency
 
* [https://www.u-blox.com/en U-Blox website]
 
* [https://www.u-blox.com/en U-Blox website]
 
** [https://www.u-blox.com/en/product/u-center U-Center software]
 
** [https://www.u-blox.com/en/product/u-center U-Center software]
 
* Set to 8 MHz on GPS PPS pin when locked
 
* 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
 
* Set to 2 Hz on GPS PPS pin when not locked
 +
 +
[[file: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
 +
 +
[[File:GPS_Antenna.jpg]]
  
 
=== FTDI ===
 
=== FTDI ===
  
−
* [[FTDI-49MM]]
+
* [[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
 +
 
 +
[[File:FTDI-P1746-CROPPED-720PX.jpg]]
  
−
=== 50 Ohm Driver ===
+
=== 50 Ohm Driver (Not Required - nice to have) ===
  
 
* Used modified [[PulseGen]] card to drive 50 Ohms, 5V level output
 
* 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
 +
 +
[[File:PulseGen_Mod_P18338-720px.jpg]]
 +
 +
=== Case ===
 +
 +
* [https://www.amazon.com/gp/product/B088HGQSZT/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1 Cabinet Door Bumpers] - used as inexpensive rubber feet
 +
** [https://www.amazon.com/s?k=Cabinet+Door+Bumpers&i=tools&ref=nb_sb_noss_2Generic search on Amazon]
 +
 +
[[File:FreqSrc-Top-01-720px.jpg]]
 +
 +
[[File: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
 +
 +
[[File:FreqSrc-Counter-01-720px.jpg]]
  
 
== Videos ==
 
== Videos ==
 +
 +
* This is the approach I followed
 +
 +
<video type="youtube">M6SmdqMA-Dg</video>
 +
 +
* GPSDO vs Rubidium Frequency Standard
  
 
<video type="youtube">CzJgEqJY3mg</video>
 
<video type="youtube">CzJgEqJY3mg</video>
 +
 +
<video type="youtube">wgq7MhM5Lk8</video>
  
 
<video type="youtube">lbns-FvpzK4</video>
 
<video type="youtube">lbns-FvpzK4</video>

Latest revision as of 13:04, 4 July 2022

Inexpensive Frequency Standard with output synchronized to GPS satellites - requires PC connection.

Version 2 build is here - does not require PC connection

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

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