Transcript Document

Noise in Amateur Radio
Receiving Systems
David Conn
VE3KL
Credit: Nasa and Jack Newton
http://antwrp.gsfc.nasa.gov/apod/ap040726.html
7/17/2015
David Conn VE3KL QCWA Oct. 2004
K = 1.38*(10-23)
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Acknowledgments
QCWA Travelers/Committee
Croft Taylor
Gus Holtz
Doug Leach
Clare Fowler
Bert Barry
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VE3CT
VE3VK
VE3XK
VE3NPC
VE3QAA
David Conn VE3KL QCWA Oct. 2004
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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
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Signal Levels
326 dBm
124 dBm
50 dBm
-73 dBm
SUN
Niagara Falls Power Generation
100 Watt Radio Transmitter
S9 at receiver front end
-144 dBm
Resistor: room temperature (I KHz BW)
-162 dBm
Sky background noise (1 KHz BW)
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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……..
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Thermal Noise Power = KTB
-144 dBm (290 K, 1 KHz BW)
Amplifier G=1
Noiseless
Bandpass Filter
B = bandwidth
Power = KToB Watts
Resistor at Temperature To
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Noise Figure, F
Effective Temperature Te
Amplifier G=1
Noisy
Bandpass Filter
B = bandwidth
Power = FKToB
= K(To +Te)B
Resistor at Temperature To
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Noise Figure Or Noise Temperature
Can use either to measure receivers
F = 1 +Te/To
Moon Temperature
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Noise Temperature
Moon, Sky, Ground
Antenna
Ideal Receiver
Thermal Radiation
Tm
Po = KTmB
Moon
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Thermal Noise …Moon
Credit:
Credit:
http://www.spacelink.msfc.n
asa.gov/Instructional.Materi
als
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
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Examples of Noise Levels
Application Noise Figure
Te
Power (dBm)
(1 KHz)
Microwave
3 dB
290
-144 dBm
HF
53 dB
57,000,000
-121
dBm….S1
Low Noise
Applications
0.7 dB
50 K
-151 dBm
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HF Man-Made Noise
Signal
+ Noise
Antenna
Balun
Power line Noise
Tx/Rx
Coiled coax
Ground
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The S Meter
► Our
Basic Power Meter
► Measures Power at the receiver input
► Usually not well calibrated
S  9  (73  PdBm ) / 6
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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
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The Radio Model: Signal and Noise
Ionosphere
Г
Isotropic
Tx
R
Rx
Power, Noise
S/N S Meter
Bandwidth
Power = 1.0 W
Transmitted
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Short Dipole
├
‫סּ‬
Loss
Doppler: limits PSK31
Amplitude distortion
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Effective Area of a Short Dipole
► Area
not a function of dipole length
► For
a 20 m dipole
Aeff = 48 square metres
► Area
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depends only on
λ2
David Conn VE3KL QCWA Oct. 2004
3 2
Aeff 

8
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Received Signal Power
Power Transmitted = 1.0 W
Received Signal Power
S units
9
8
7
6
5
4
3
2
1
100
1000
10000
Distance
100000
[Km]
Ae ff = 1.0 s quar e m e tr e10
s s quare m e tr e s
100 s quar e m e tr e s
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G G 2
1000 s quare m e tr e s
David Connt VE3KL
QCWA Oct. 2004
r
Pr  Pt
(4R 2 )
[ Watts ] Gt  1.0
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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
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to S units for our use.
David Conn VE3KL QCWA Oct. 2004
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ITU Noise Data (Field Strength)
Man-M ade Noise Levels
Field Strength dB (uv/m)
De rived from ITU-R P. 372-7
10
5
0
-5
-10
-15
-20
-25
0
4
8
12
16
20
24
28
Fre quency [M Hz]
Quie t Rural
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Rural
David Conn VE3KL QCWA Oct. 2004
Re side ntial
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Noise in SSB : BW = 2700 Hz
Man-Made Noise Levels
Received Power [S units]
SSB ( 2.7 KHz Bandw idth )
9
8
7
6
5
4
3
2
1
0
0
4
8
12
16
20
24
28
Frequency [MHz]
Quiet Rural
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Rural
David Conn VE3KL QCWA Oct. 2004
Residential
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Noise In CW : BW = 500 Hz
M an-M ade Nois e Le ve ls
Received Power [S Units]
CW (500 Hz Bandw idth)
9
8
7
6
5
4
3
2
1
0
0
4
8
12
16
20
24
28
Frequency [MHz]
Quiet Rural
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Rural
David Conn VE3KL QCWA Oct. 2004
Residential
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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
C  BLog 2 (1  P / N) bits / s
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Noise in PSK31 BW = 62.5 Hz
Man-Made Noise Levels
PSK 31 ( 62.5 Hz Bandw idth )
Received Power [S units]
9
8
7
6
5
4
3
2
1
0
0
4
8
12
16
20
24
28
Frequency [MHz]
Quiet Rural
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Rural
David Conn VE3KL QCWA Oct. 2004
Residential
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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?
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Filter External Cable Noise: Use a PI network
Signal
+ Noise
Antenna
Balun
Power line Noise
Tx/Rx
Coiled coax
Ground
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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
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Thanks for Attending
73 David
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Following are back up slides
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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
2
 D 
G  10Log{0.55
 }
  
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The Shannon Hartley Limit
CW Morse Code: P/N = 3 S units
IF C = 20 words per minute
Then: B = 1.4 Hz
C  BLog 2 (1  P / N) bits / s
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Effective Area
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Effective Area: Yagi
A three element 10 m Yagi, free space
Gain = 8.4 dB
Aeff = 55 square Metres
2
Aeff  Gain *
4
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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
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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
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