Noise in Amateur Radio Receiving Systems

04/19/23 David Conn VE3KL QCWA Oct. 2004 1

Noise in Amateur Radio Noise in Amateur Radio Receiving SystemsReceiving Systems

David Conn VE3KLDavid Conn VE3KL

K = 1.38*(10-23)Credit: Nasa and Jack Newton

http://antwrp.gsfc.nasa.gov/apod/ap040726.html


AcknowledgmentsAcknowledgments

QCWA Travelers/CommitteeQCWA Travelers/Committee

Croft TaylorCroft Taylor VE3CT VE3CT

Gus HoltzGus Holtz VE3VK VE3VK

Doug Leach VE3XKDoug Leach VE3XK

Clare Fowler VE3NPCClare Fowler VE3NPC

Bert Barry VE3QAABert Barry VE3QAA


IntroductionIntroduction

►A talk about noise levels in amateur radio A talk about noise levels in amateur radio systems: SSB, CW, PSK31, EME…systems: SSB, CW, PSK31, EME…

►Noise Types: Thermal, Shot, Flicker Noise Types: Thermal, Shot, Flicker atmospheric, man-made……atmospheric, man-made……

►Measured with an ideal S meterMeasured with an ideal S meterSignal Levels


Signal LevelsSignal Levels326 dBm SUN

Niagara Falls Power Generation

100 Watt Radio Transmitter

S9 at receiver front end

Resistor: room temperature (I KHz BW)

Sky background noise (1 KHz BW)

50 dBm

-73 dBm

-144 dBm

124 dBm

-162 dBm


Noise TypesNoise Types

► Thermal: Moving electrons in conductors : KTBThermal: Moving electrons in conductors : KTB

► Shot: DC current flow in semiconductorsShot: DC current flow in semiconductors

► Flicker or 1/f noise: like earth quakes in Flicker or 1/f noise: like earth quakes in devicesdevices

► Man-made : Can propagate via ionospheric Man-made : Can propagate via ionospheric skipskip

► Atmospheric/ionospheric/sky……..Atmospheric/ionospheric/sky……..


Thermal Noise Power = KTBThermal Noise Power = KTB-144 dBm (290 K, 1 KHz BW)-144 dBm (290 K, 1 KHz BW)

Resistor at Temperature To

Power = KToB Watts

Amplifier G=1Noiseless

Bandpass FilterB = bandwidth


Noise Figure, FNoise Figure, FEffective Temperature TeEffective Temperature Te

Resistor at Temperature To

Power = FKToB = K(To +Te)B

Amplifier G=1

NoisyBandpass FilterB = bandwidth


Noise Figure Or Noise Noise Figure Or Noise TemperatureTemperature

Can use either to measure receiversCan use either to measure receivers

F = 1 +Te/To

Moon Temperature


Noise TemperatureNoise TemperatureMoon, Sky, GroundMoon, Sky, Ground

Moon

Tm Po = KTmB

Thermal Radiation

Antenna

Ideal Receiver


Thermal Noise …MoonThermal Noise …Moon

Moon Temperature 510 K Oct 17, 2004: -141 dBm (1KHz)Varies with time: 510 K is poor for EME Communications

http://www.vhfdx.net/w5luu.html

http://www.spacelink.msfc.nasa.gov/Instructional.Materials

Credit: Credit:


Examples of Noise LevelsExamples of Noise Levels

ApplicatioApplicationn

Noise Noise FigureFigure

TeTe Power Power (dBm) (1 (dBm) (1 KHz)KHz)

MicrowaveMicrowave 3 dB3 dB 290290 -144 dBm-144 dBm

HFHF 53 dB53 dB 57,000,0057,000,0000

-121 -121 dBm….S1dBm….S1

Low Noise Low Noise ApplicatioApplicationsns

0.7 dB0.7 dB 50 K50 K -151 dBm-151 dBm


HF Man-Made NoiseHF Man-Made Noise

Ground

Antenna

Tx/RxCoiled coax

Power line NoiseBalun

Signal+ Noise


The S MeterThe S Meter

►Our Basic Power MeterOur Basic Power Meter►Measures Power at the receiver input Measures Power at the receiver input ►Usually not well calibratedUsually not well calibrated

6/)73(9 dBmPS


Definition of TermsDefinition of Terms

► S is the reading on an S meter.S is the reading on an S meter.

► Field strength (Volts/m) is a measure of Field strength (Volts/m) is a measure of the electric field strength at the receiverthe electric field strength at the receiver

► Aeff is the effective area of a lossless Aeff is the effective area of a lossless antenna, related to directivityantenna, related to directivity


The Radio Model: Signal The Radio Model: Signal andand NoiseNoise

Ionosphere

RxTx

Power = 1.0 WTransmitted

Power, NoiseS/N S MeterBandwidth

LossDoppler: limits PSK31Amplitude distortionּס

├Isotropic Short Dipole

R

Г


Effective Area of a Short DipoleEffective Area of a Short Dipole

►Area not a function of dipole lengthArea not a function of dipole length

►For a 20 m dipoleFor a 20 m dipole

Aeff = 48 square metresAeff = 48 square metres

►Area depends only on Area depends only on λλ222

8

3Aeff


Received Signal Power Received Signal Power Power Transmitted = 1.0 WPower Transmitted = 1.0 W

123456789

S u

nit

s

100 1000 10000 100000

Distance [Km]

Aeff = 1.0 square metres10 square metres

100 square metres 1000 square metres

Received Signal Power

0.1Gt]Watts[)R4(

GGPP

2

2rt

tr


Man-Made Noise AnalysisMan-Made Noise Analysis

►Data from ITU-R P.372-7 ReportData from ITU-R P.372-7 Report

►Man-made noise relative to thermal Man-made noise relative to thermal noise. Not dependent on the bandwidthnoise. Not dependent on the bandwidth

►Translate to S units for our use. Translate to S units for our use.


ITU Noise ITU Noise DataData (Field (Field Strength)Strength)

-25

-20

-15

-10

-5

0

5

10

Fie

ld S

tren

gth

dB

(u

v/m

)

0 4 8 12 16 20 24 28Frequency [MHz]

Quiet Rural Rural Residential

Man-Made Noise LevelsDerived from ITU-R P. 372-7


Noise in SSB : BW = 2700 HzNoise in SSB : BW = 2700 Hz

0123456789

Receiv

ed

Po

wer

[S u

nit

s]

0 4 8 12 16 20 24 28Frequency [MHz]


Man-Made Noise LevelsSSB ( 2.7 KHz Bandwidth )


Noise In CW : BW = 500 HzNoise In CW : BW = 500 Hz

0123456789

Receiv

ed

Po

wer

[S

Un

its]

0 4 8 12 16 20 24 28Frequency [MHz]


Man-Made Noise LevelsCW (500 Hz Bandwidth)


The Shannon Hartley LimitThe Shannon Hartley Limit

CW Morse Code: P/N = 3 S units, CW Morse Code: P/N = 3 S units,

B= 100HzB= 100Hz

Then: C = Then: C = 14381438 words per minute words per minute

P is the signal powerP is the signal power

N is the noise powerN is the noise power

B is the receiver bandwidthB is the receiver bandwidth

s/bits)N/P1(BLogC 2


Noise in PSK31 BW = 62.5 HzNoise in PSK31 BW = 62.5 Hz

0123456789

Receiv

ed

Po

wer [

S u

nit

s]

0 4 8 12 16 20 24 28Frequency [MHz]


Man-Made Noise LevelsPSK 31 ( 62.5 Hz Bandwidth )


Solutions to the Noise ProblemSolutions to the Noise Problem

►Keep antennas away from houses and Keep antennas away from houses and power lines.power lines.

►Use a Balun at the antennaUse a Balun at the antenna►Use shielded coax cables for best results.Use shielded coax cables for best results.►Use a grounding system to suppress Use a grounding system to suppress

noise that comes from currents flowing noise that comes from currents flowing up to the antenna on the outside of the up to the antenna on the outside of the coax.coax.

►Bury the coax cable: moisture problem?Bury the coax cable: moisture problem?


Filter External Cable Noise: Use a PI Filter External Cable Noise: Use a PI networknetwork

Ground

Antenna

Tx/RxCoiled coax

Power line NoiseBalun

Signal+ Noise


SummarySummary

►Man-made Noise Dominates at MF/HFMan-made Noise Dominates at MF/HF

►EME requires low temp receiversEME requires low temp receivers

►No need for very low noise receivers at No need for very low noise receivers at HFHF

►HF receivers need high dynamic rangeHF receivers need high dynamic range


Thanks for AttendingThanks for Attending

73 David73 David


Following are back up slidesFollowing are back up slides


Effective Area: Parabolic DishEffective Area: Parabolic Dish

A 2 metre parabolic dishA 2 metre parabolic dish

Freq = 1296 MHzFreq = 1296 MHz

Wavelength = 23.8 cmWavelength = 23.8 cm

Physical area = 3.14 square metresPhysical area = 3.14 square metres

Aeff = 1.73 square metresAeff = 1.73 square metres

}D

55.0{Log10G2


The Shannon Hartley LimitThe Shannon Hartley Limit

CW Morse Code: P/N = 3 S unitsCW Morse Code: P/N = 3 S units

IF C = 20 words per minuteIF C = 20 words per minute

Then: B = Then: B = 1.41.4 Hz Hz

s/bits)N/P1(BLogC 2


Effective Area Effective Area


Effective Area: YagiEffective Area: Yagi

A three element 10 m Yagi, free spaceA three element 10 m Yagi, free space

Gain = 8.4 dBGain = 8.4 dB

Aeff = 55 square MetresAeff = 55 square Metres

4

*GainAeff2


SummarySummary

►Main output: S meter graphs for SSBMain output: S meter graphs for SSB►You can use these graphs to evaluate You can use these graphs to evaluate

your own locationyour own location►We have a long way to go to get close to We have a long way to go to get close to

the Shannon - Hartley limitthe Shannon - Hartley limit►The issue of noise pollution needs our The issue of noise pollution needs our

attention and careful measurementsattention and careful measurements


Where to Get More InformationWhere to Get More Information

► RAC Web site: look there firstRAC Web site: look there first► ARRL Web siteARRL Web site► Details in my web site as it developsDetails in my web site as it develops► Fields and Waves in Communication Fields and Waves in Communication

Electronics: Ramo, Whinnery, Van Duzer ; Electronics: Ramo, Whinnery, Van Duzer ; John Wiley, third edition, 1994, ISBN 0-0471-John Wiley, third edition, 1994, ISBN 0-0471-58551-358551-3

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Noise in Amateur Radio Receiving Systems