Noise in Amateur Radio Receiving Systems

1. David Conn VE3KL Noise in Amateur Radio Receiving Systems Credit: Nasa and Jack Newton K = 1.38*(10-23) http://antwrp.gsfc.nasa.gov/apod/ap040726.html David Conn VE3KL QCWA Oct. 2004

2. QCWA Travelers/Committee Croft Taylor VE3CT Gus Holtz VE3VK Doug Leach VE3XK Clare Fowler VE3NPC Bert Barry VE3QAA Acknowledgments David Conn VE3KL QCWA Oct. 2004

3. Introduction • A talk about noise levels in amateur radio systems: SSB, CW, PSK31, EME… • Noise Types: Thermal, Shot, Flicker atmospheric, man-made…… • Measured with an ideal S meter Signal Levels David Conn VE3KL QCWA Oct. 2004

4. Signal Levels 326 dBm SUN 124 dBm Niagara Falls Power Generation 50 dBm 100 Watt Radio Transmitter -73 dBm S9 at receiver front end Resistor: room temperature (I KHz BW) -144 dBm Sky background noise (1 KHz BW) -162 dBm David Conn VE3KL QCWA Oct. 2004

5. Noise Types • Thermal: Moving electrons in conductors : KTB • Shot: DC current flow in semiconductors • Flicker or 1/f noise: like earth quakes in devices • Man-made : Can propagate via ionospheric skip • Atmospheric/ionospheric/sky…….. David Conn VE3KL QCWA Oct. 2004

6. Thermal Noise Power = KTB-144 dBm (290 K, 1 KHz BW) Bandpass Filter B = bandwidth Amplifier G=1 Noiseless Power = KToB Watts Resistor at Temperature To David Conn VE3KL QCWA Oct. 2004

7. Noise Figure, FEffective Temperature Te Bandpass Filter B = bandwidth Amplifier G=1 Noisy Power = FKToB = K(To +Te)B Resistor at Temperature To David Conn VE3KL QCWA Oct. 2004

8. Noise Figure Or Noise TemperatureCan use either to measure receivers F = 1 +Te/To Moon Temperature David Conn VE3KL QCWA Oct. 2004

9. Noise TemperatureMoon, Sky, Ground Antenna Ideal Receiver Thermal Radiation Po = KTmB Tm Moon David Conn VE3KL QCWA Oct. 2004

10. Thermal Noise …Moon Credit: Credit: http://www.spacelink.msfc.nasa.gov/Instructional.Materials http://www.vhfdx.net/w5luu.html Moon Temperature 510 K Oct 17, 2004: -141 dBm (1KHz) Varies with time: 510 K is poor for EME Communications David Conn VE3KL QCWA Oct. 2004

11. Examples of Noise Levels David Conn VE3KL QCWA Oct. 2004

12. HF Man-Made Noise Signal + Noise Antenna Balun Power line Noise Coiledcoax Tx/Rx Ground David Conn VE3KL QCWA Oct. 2004

13. The S Meter • Our Basic Power Meter • Measures Power at the receiver input • Usually not well calibrated David Conn VE3KL QCWA Oct. 2004

14. Definition of Terms • S is the reading on an S meter. • Field strength (Volts/m) is a measure of the electric field strength at the receiver • Aeff is the effective area of a lossless antenna, related to directivity David Conn VE3KL QCWA Oct. 2004

15. The Radio Model: Signal and Noise Ionosphere Г Loss Doppler: limits PSK31 Amplitude distortion Isotropic Short Dipole סּ ├ Rx Tx R Power, Noise S/N S Meter Bandwidth Power = 1.0 W Transmitted David Conn VE3KL QCWA Oct. 2004

16. Effective Area of a Short Dipole • Area not a function of dipole length • For a 20 m dipole Aeff = 48 square metres • Area depends only on λ2 David Conn VE3KL QCWA Oct. 2004

17. Received Signal Power Power Transmitted = 1.0 W David Conn VE3KL QCWA Oct. 2004

18. Man-Made Noise Analysis • Data from ITU-R P.372-7 Report • Man-made noise relative to thermal noise. Not dependent on the bandwidth • Translate to S units for our use. David Conn VE3KL QCWA Oct. 2004

19. ITU Noise Data (Field Strength) David Conn VE3KL QCWA Oct. 2004

20. Noise in SSB : BW = 2700 Hz David Conn VE3KL QCWA Oct. 2004

21. Noise In CW : BW = 500 Hz David Conn VE3KL QCWA Oct. 2004

22. The Shannon Hartley Limit CW Morse Code: P/N = 3 S units, B= 100Hz Then: C = 1438 words per minute P is the signal power N is the noise power B is the receiver bandwidth David Conn VE3KL QCWA Oct. 2004

23. Noise in PSK31 BW = 62.5 Hz David Conn VE3KL QCWA Oct. 2004

24. Solutions to the Noise Problem • Keep antennas away from houses and power lines. • Use a Balun at the antenna • Use shielded coax cables for best results. • Use a grounding system to suppress noise that comes from currents flowing up to the antenna on the outside of the coax. • Bury the coax cable: moisture problem? David Conn VE3KL QCWA Oct. 2004

25. Filter External Cable Noise: Use a PI network Signal + Noise Antenna Balun Power line Noise Coiledcoax Tx/Rx Ground David Conn VE3KL QCWA Oct. 2004

26. Summary • Man-made Noise Dominates at MF/HF • EME requires low temp receivers • No need for very low noise receivers at HF • HF receivers need high dynamic range David Conn VE3KL QCWA Oct. 2004

27. Thanks for Attending73 David David Conn VE3KL QCWA Oct. 2004

28. Following are back up slides David Conn VE3KL QCWA Oct. 2004

29. Effective Area: Parabolic Dish A 2 metre parabolic dish Freq = 1296 MHz Wavelength = 23.8 cm Physical area = 3.14 square metres Aeff = 1.73 square metres David Conn VE3KL QCWA Oct. 2004

30. The Shannon Hartley Limit CW Morse Code: P/N = 3 S units IF C = 20 words per minute Then: B = 1.4 Hz David Conn VE3KL QCWA Oct. 2004

31. Effective Area David Conn VE3KL QCWA Oct. 2004

32. A three element 10 m Yagi, free space Gain = 8.4 dB Aeff = 55 square Metres Effective Area: Yagi David Conn VE3KL QCWA Oct. 2004

33. Summary • Main output: S meter graphs for SSB • You can use these graphs to evaluate your own location • We have a long way to go to get close to the Shannon - Hartley limit • The issue of noise pollution needs our attention and careful measurements David Conn VE3KL QCWA Oct. 2004

34. Where to Get More Information • RAC Web site: look there first • ARRL Web site • Details in my web site as it develops • Fields and Waves in Communication Electronics: Ramo, Whinnery, Van Duzer ; John Wiley, third edition, 1994, ISBN 0-0471-58551-3 David Conn VE3KL QCWA Oct. 2004