MAX2870 signal generator using a UBLOX GPS as a reference clock

The github link below provides photos showing the hardware setup and the Ublox U-Center GUI screen.
github.com/pgiacalo/MAX2870_S...
Note that the output of the GPS unit is terminated with 50 ohms and a DC block is placed in front of the MAX2870 reference clock input. This was done to protect the MAX2870 clock input circuit. Also, the MAX2870 requires reference clock signal that is a SQUARE wave with a peak-to-peak voltage of 2 to 3 volts.
The UBLOX GPS units can produce 140 jitter-free frequencies. These 140 are the factors of 24 million (i.e., 24 MHz). The list of all 140 factors/frequencies is shown here:
www.calculatorsoup.com/calcul...
See the video below for a further explanation on why these specific frequencies produce the best output signals (i.e., signals without jitter).
• UBLOX GPS as a variabl...

Пікірлер: 2

  • @cameramaker
    @cameramaker11 күн бұрын

    Does the uBlox provide a digital signal that tells that the frequency is GPS synchronized and not just a local XO ? or one has to query the status over the serial interface for that?

  • @philipgiacalone5605

    @philipgiacalone5605

    10 күн бұрын

    Using the serial interface is likely the easiest way, by parsing the NMEA messages, as you likely already know. I understand that uBlox also supports a binary UBX Protocol that can be accessed via UART. This provides a UBX-NAV-STATUS message with a field to indicate whether there is a valid GPS fix. I'm not sure which uBlox devices support this protocol or whether is is enabled by default. Just for reference, here is some more info about these two approaches: Using NMEA -------------------- The "Fix Quality" field in the $GPGGA message indicates whether or not a valid GPS fix has been obtained (Fix Quality values: 0: Invalid, 1: GPS fix, 2: DGPS fix). Example NMEA messages: 1. NMEA Message with a Valid GPS Fix $GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47 2. NMEA Message without a Valid GPS Fix $GPGGA,123520,,,,,,0,00,99.99,,,,,,*48 List of NMEA fields from the `$GPGGA` sentence, in order with definitions: 1. **Sentence Identifier** (`$GPGGA`): - **$GPGGA**: Global Positioning System Fix Data 2. **UTC Time** (`hhmmss.sss`): - **123519**: Fix taken at 12:35:19 UTC 3. **Latitude** (`ddmm.mmmm`): - **4807.038**: Latitude in degrees and minutes (48 degrees 07.038 minutes) 4. **North/South Indicator** (`N/S`): - **N**: North 5. **Longitude** (`dddmm.mmmm`): - **01131.000**: Longitude in degrees and minutes (11 degrees 31.000 minutes) 6. **East/West Indicator** (`E/W`): - **E**: East 7. **Fix Quality** (`x`): - **1**: Fix quality (0 = invalid, 1 = GPS fix, 2 = DGPS fix) 8. **Number of Satellites** (`xx`): - **08**: Number of satellites being tracked 9. **Horizontal Dilution of Precision (HDOP)** (`x.x`): - **0.9**: Horizontal Dilution of Precision 10. **Altitude** (`x.x`): - **545.4**: Altitude above mean sea level in meters 11. **Units of Altitude** (`M`): - **M**: Meters 12. **Height of Geoid Above WGS84 Ellipsoid** (`x.x`): - **46.9**: Height of geoid (mean sea level) above WGS84 ellipsoid in meters 13. **Units of Geoid Height** (`M`): - **M**: Meters 14. **Time Since Last DGPS Update** (`x.x`): - **(empty)**: Time in seconds since last DGPS update (blank if not available) 15. **DGPS Station ID** (`xxxx`): - **(empty)**: DGPS station ID (blank if not available) 16. **Checksum** (`*hh`): - **47**: Checksum for the sentence Using UBX Protocol ----------------------------------- The UBX Protocol provides a UBX-NAV-STATUS message that includes a "gpsFix" field to indicate the GPS fix status. Example UBX-NAV-STATUS Message: UBX-NAV-STATUS iTOW: 123456789 gpsFix: 3 fixStat: 0 flags: 0x01 ttff: 4000 msss: 5000 gpsFix values and meaning: 0: No Fix 2: 2D Fix 3: 3D Fix 4: DGPS Fix 5: Time-only Fix