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Frequency References

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  1. Frequency References For Radio Amateurs Prepared by Murray Greenman ZL1BPU Email: as149@detroit.freenet.org QRV: 3560 kHz LSB, Klondyke 6625 Address: QTHR as149@detroit.freenet.org

  2. Frequency References What is a Frequency Reference? • A tool for measuring radio frequency accurately • A stable signal source of known frequency error and drift rate as149@detroit.freenet.org

  3. Frequency References What use is a Frequency Reference? • Regulatory Requirement • Accurate measurement • Equipment calibration as149@detroit.freenet.org

  4. Frequency Reference - Uses Regulatory Requirement • The Radiocommunications Act 1989 says that Amateurs need to have “a reliable means for determining the operating radio frequency.”(Nothing is said about the required accuracy or traceability!) as149@detroit.freenet.org

  5. Frequency Reference - Uses Accurate measurement • Especially important for weak signal DX • Frequency Measuring Contest • Drift tracking • Doppler measurement Receiver warmup drift as149@detroit.freenet.org

  6. Frequency Reference - Uses Equipment Calibration • Reference for frequency counter • Counter calibration • Transceiver & receiver calibration as149@detroit.freenet.org

  7. Frequency References History of Amateur References • Wavemeters and grid-dip meters • Crystal oscillators, heterodyne meters • Digital frequency counters • TCXO and OCXO references • TV and satellite based references as149@detroit.freenet.org

  8. Frequency Reference - History Amateur Wavemeters 1930s - • Tuned circuit and light-bulb units • “Lecher lines” for VHF • Microwave cavity wavemeters • Grid Dip Meters Heathkit GD-1B Grid-Dip Meter as149@detroit.freenet.org

  9. Frequency Reference - History Amateur Crystal Oscillators • First crystal oscillators used 1930s • Stable and accurate crystals 1950s • 100 kHz osc & digital dividers 1970s • TCXO and OCXO use – 1990s as149@detroit.freenet.org

  10. Frequency Reference - History Heterodyne Meters • War surplus • Class D Wavemeter (British Army) • No. 10 Calibrator (British Army) • BC221 Heterodyne meter (US Army) • LM10 Heterodyne meter (US Navy) No. 10 Calibrator as149@detroit.freenet.org

  11. Frequency Reference - History Frequency Counters • TTL logic 1963 SN74xx family • LED displays 1970s • DSE kit counter 1988 • Accuracy poor ±10 ppmwithout TCXO as149@detroit.freenet.org

  12. Frequency Reference - History Temperature Compensated Oscillators • First analog TCXO 1959 • Digital compensation 1970s • Microprocessor compensation 1984 • Accuracy ± 0.5 ppm -40 °C to +75 °C as149@detroit.freenet.org

  13. Frequency Reference Temperature Compensated Oscillators • Inexpensive • Low power • Small size • Wide temperature range, fast warmup as149@detroit.freenet.org

  14. Frequency Reference - History Oven Controlled Crystal Oscillators • AT-cut overtone oscillator 1955 • Ageing rate 1 in 10-9 / day by 1960 • Power 25W in 1950, 2W 1970 • Accuracy 1 in 10-9 over wide temp range as149@detroit.freenet.org

  15. Frequency Reference Oven Controlled Crystal Oscillators • Very low noise, very long life • Low ageing rate, 10-10 / day • Moderate power (2W) • Must be operated continuously as149@detroit.freenet.org

  16. Frequency Reference TV References • Simple on-screen comparison 1 MHz ÷64 • TV Line Frequency PLL Reference* • TV Colour Subcarrier 4433618.75 Hz† * Ian Pogson Electronics Australia, Nov 1986 † DSIR Physics and Engineering Laboratory technical paper, 1975/26 as149@detroit.freenet.org

  17. Frequency Reference - History Satellite References • Transit satellite system, 1980s • Global Positioning Satellites 1990 • Brooks Shera W5OJM design 1998 • GPS 1 second tick accuracy better than 1us(note - NMEA time data not accurate enough) as149@detroit.freenet.org

  18. Frequency References Frequency References Where do I find a Frequency Reference? • Use a TXCO from an old cellular phone • Buy an inexpensive TCXO • OCXO from old “Transit” satellite navigators • Build your own OCXO • Build a simple TV locked reference as149@detroit.freenet.org

  19. Frequency References Frequency References Temperature Controlled Xtal Oscillator sources • TXCO used in every cellular phone • Look for older phones - • Bigger and easier to use • Useful frequencies, 5.12 and 10.24 MHz • Rakon will make any frequency to order • 10 Mhz units “off the shelf” about $30 as149@detroit.freenet.org

  20. Frequency References Frequency References Oven Controlled Xtal Oscillator sources • Transit satellite navigation receivers • Service is now defunct, receivers useless • Receiver contains very high quality 5 MHz OCXO • Short term 1 in 1010, ageing typically 1 in 109 / day • Look for Magnavox MX 4102 - often given away The Magnavox MX 4102 as149@detroit.freenet.org

  21. Frequency References Frequency References Building an OCXO • Use a high quality oven crystal 2 - 5 MHz • Build a robust well insulated oven • Use analog control and transistor heater • Build oscillator and buffers inside oven • Use well regulated power supplies • Adjust oven temperature to crystal plateau • Operate oscillator continuously as149@detroit.freenet.org

  22. Frequency References Frequency References Building a TV controlled reference • Use a voltage controlled TCXO or OCXO • Divide to 1 MHz, then by 64 to 15.625 kHz • Use 15.625 kHz TV line frequency • Use TV1 or TV2 only (Rubidium standard) • Simple design in Electronics Aust, Nov 1986 as149@detroit.freenet.org

  23. Frequency References Frequency References Calibrating your reference • DO NOT USE WWV or VNG! • Received frequency varies at least 1 in 106 as149@detroit.freenet.org

  24. Frequency References Frequency References Calibrating your reference • Use TV line frequency • TV locked reference or beat on TV screen • Oscilloscope or phase meter method • Frequency counter long gate time method • Use GPS disciplined reference as149@detroit.freenet.org

  25. Frequency References Frequency References Calibrate your reference regularly • Slowly adjust frequency as near as possible • Zero beat method not practical • Oscilloscope and phase meter methods best • Write down date, offset, ageing rate • Performance will generally improve with age as149@detroit.freenet.org