Last update: 20-May-2002

High Precision GPS/TV controlled Reference Oscillator

 Published in the HAM Radio Magazine CQ-DL 9/2001 and 10/2001, the periodical of the German Amateur Radio Club ( DARC).

Can be used as:
  • Measuring Instrument without disciplined Oscillator,
    for assessment of thermal, own short therm and long term stability, for startup and switch-on characteristics of oscillators up to 130MHz.
  • Controled loop for disciplined Oscillators,
    for oscillators up to 130MHz.

Reference sources:
  • GPS : 1PPS-Pulse
  • TV    : FBAS
  • and other precise references based on a 1 second pulse. 

Principle of work:
  • Phase meter between 2 pulses with a resolution of 10ns.

  • For high precise oscillators (HP10544,HP10811,Rb-standard,etc),till home-brewed local oscillators (LOs) with reduced precision but extended tuning range.
  • Infinitely variable oscillator control profiles with dynamic regulation characteristics.

Hardware features:
  • Digital part with micro controller (8051 derivative), indicating system, optional LC-Display (2*16 character) and control elements (4 push buttons).
  • Equipped with re-programmable FPGA's .
  • On board Sync. separator for FBAS TV signal.
  • Displays the current status of the system on optional 2-line LCD.
  • 4 push buttons for system setup, guided by software on LCD.
  • Status display and setup also possible via PC link.
  • Menu for reference source selection
    GPS: 1PPS or other similar 1 second pulses.

    TV   : FBAS, on board I2C interface (including setup software) for direct TV-tuner            setup for terrestrial and cable transmitter.
  • Saving of all important setup and other dynamic created values in EEPROM.
  • Analog part consist of a 20 bit DAC and a high precision voltage reference with extremely low temperature coefficient.

 Indicating System:
  • Synchronized phase meter injection frequency using a PLL. (Error reduction better than 1*10exp-14).
  • Synchronized phase meter.
  • Self-contained fast synchronization mechanism between the reference and oscillator for optimal adjustment of the tuning range.
  • Reference and oscillator frequency (1PPS,FBAS etc.) supervisor as protection about drop-out and absence.
  • Poor signal recognizer can suppress regulation and may try re-syncronization automatically.
  • Setup to last DAC value in case of start up after power fail.
  • Power reserve if reference signal fails.

Processor Software:
  • Processor SW in system programmable (ISP ,for maintaining and SW update).
  • Self-contained recording of the oscillator characteristic curve .
  • Inverse characteristic curve recognizer.
  • Status display of current values of the regulation characteristics.
  • Display of all automatically generated settings for verification.
  • System soft-start feature.
  • System cold-start feature.
  • System default setup.
  • Selectable worm-up time after new start-up.
  • Mostly all regulation characteristic parameters can be chosen by the user to get an optimal alignment for the used oscillator.
  • Statistic function for signal quality and two step failure counter.
  • Diagnostic function for regulation loop (100sec Loop).
  • Software based rough and fine adjustment for oscillators.
  • Diagnostic and test function for analog part.
  • On-line calculation of the current precision using linear regression.
  • Recognition algorithm for short term frequency deviation.
  • RS232 connection to a PC or data logger board. Any phase counter result and other important information will be transmitted via RS232 second by second.

Data Logger Board:
  • Optional data logger board for collecting data for statistics. Future version will have a connection to a PR TNC for remote control.

PC Software Tools:
  • On-line analysis and statistics using different methods.
  • Off-line analysis and statistics using different methods.
  • Up/Download Tool for all relevant parameters of the unit. Can display all values like the display at the LCD.Can save, load and print everything for documentation, including the frequency response characteristic curve.
  • Download/Setup Program for data logger board.
  • GPS Satellite Statistic Tool for GPS satellite availability.

 Complete Documentation for the CRO- Project:



 Additional hardware for that project:

  • Board for LCD-Display and keys, CRO-LCD

 Some results for example:

Interessted in reproduction?


Ask the CRO-team for what you need.

e-mail Addresse [email protected]



If you send a CD and a SAE with sufficient letter rate to the address below, you may get all documentation and all tools via mail.


Klaus Osterschek
Marienberger Str. 29A
D-83135 Schechen

  For very helpfull support and ideas thanks a lot to :
   ( in alphabetic order)

Andreas Gawron, DF7YC Alexander Görich 
Lutz Hannig, DL9GI Andreas Mangler, DD4IV
Dr. Helmut Rapp, DL1HEL  


and many many others.



The CRO-Team:               Here we are !      

e-mail Addresse [email protected]

Back to homepage

Back to CRO start page

Top of this page