Noise in Amateur Radio Receiving Systems David Conn

Noise in Amateur Radio Receiving Systems David Conn VE 3 KL Credit: Nasa and Jack Newton http: //antwrp. gsfc. nasa. gov/apod/ap 040726. html 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 K = 1. 38*(10 -23) 1

Acknowledgments QCWA Travelers/Committee Croft Taylor Gus Holtz Doug Leach Clare Fowler Bert Barry 5/25/2021 VE 3 CT VE 3 VK VE 3 XK VE 3 NPC VE 3 QAA David Conn VE 3 KL QCWA Oct. 2004 2

Introduction ► A talk about noise levels in amateur radio systems: SSB, CW, PSK 31, EME… ► Noise Types: Thermal, Shot, Flicker atmospheric, man-made…… ► Measured with an ideal S meter Signal Levels 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 3

Signal Levels 326 d. Bm 124 d. Bm 50 d. Bm -73 d. Bm SUN Niagara Falls Power Generation 100 Watt Radio Transmitter S 9 at receiver front end -144 d. Bm Resistor: room temperature (I KHz BW) -162 d. Bm Sky background noise (1 KHz BW) 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 4

Noise Types ► Thermal: ► Shot: Moving electrons in conductors : KTB 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……. . 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 5

Thermal Noise Power = KTB -144 d. Bm (290 K, 1 KHz BW) Amplifier G=1 Noiseless Bandpass Filter B = bandwidth Power = KTo. B Watts Resistor at Temperature To 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 6

Noise Figure, F Effective Temperature Te Amplifier G=1 Noisy Bandpass Filter B = bandwidth Power = FKTo. B = K(To +Te)B Resistor at Temperature To 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 7

Noise Figure Or Noise Temperature Can use either to measure receivers F = 1 +Te/To Moon Temperature 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 8

Noise Temperature Moon, Sky, Ground Antenna Ideal Receiver Thermal Radiation Tm Po = KTm. B Moon 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 9

Thermal Noise …Moon Credit: http: //www. spacelink. msfc. nasa. gov/Instructional. Mate rials http: //www. vhfdx. net/w 5 luu. html Moon Temperature 510 K Oct 17, 2004: -141 d. Bm (1 KHz) Varies with time: 510 K is poor for EME Communications 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 10

Examples of Noise Levels Application Noise Figure Te Power (d. Bm) (1 KHz) Microwave 3 d. B 290 -144 d. Bm HF 53 d. B 57, 000 -121 d. Bm…. S 1 Low Noise Applications 0. 7 d. B 50 K -151 d. Bm 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 11

HF Man-Made Noise Signal + Noise Antenna Balun Power line Noise Tx/Rx Coiled coax Ground 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 12

The S Meter ► Our Basic Power Meter ► Measures Power at the receiver input ► Usually not well calibrated 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 13

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 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 14

The Radio Model: Signal and Noise Ionosphere Isotropic Tx Loss Doppler: limits PSK 31 Amplitude distortion R Rx Power, Noise S/N S Meter Bandwidth Power = 1. 0 W Transmitted 5/25/2021 Short Dipole ├ סּ Г David Conn VE 3 KL QCWA Oct. 2004 15

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 λ 2 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 16

Received Signal Power Transmitted = 1. 0 W 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 17

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. 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 18

ITU Noise Data (Field Strength) 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 19

Noise in SSB : BW = 2700 Hz 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 20

Noise In CW : BW = 500 Hz 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 21

The Shannon Hartley Limit CW Morse Code: P/N = 3 S units, B= 100 Hz Then: C = 1438 words per minute P is the signal power N is the noise power B is the receiver bandwidth 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 22

Noise in PSK 31 BW = 62. 5 Hz 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 23

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? 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 24

Filter External Cable Noise: Use a PI network Signal + Noise Antenna Balun Power line Noise Tx/Rx Coiled coax Ground 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 25

Summary ► Man-made ► EME Noise Dominates at MF/HF requires low temp receivers ► No need for very low noise receivers at HF ► HF receivers need high dynamic range 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 26

Thanks for Attending 73 David 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 27

Following are back up slides 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 28

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 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 29

The Shannon Hartley Limit CW Morse Code: P/N = 3 S units IF C = 20 words per minute Then: B = 1. 4 Hz 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 30

Effective Area 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 31

Effective Area: Yagi A three element 10 m Yagi, free space Gain = 8. 4 d. B Aeff = 55 square Metres 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 32

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 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 33

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 5/25/2021 David Conn VE 3 KL QCWA Oct. 2004 34