propagation of electromagnetic waves
DESCRIPTION
PROPAGATION OF ELECTROMAGNETIC WAVES. HOW DOES MY SIGNAL GET FROM HERE TO THERE? By Forest Cummings, W5LQU And Dave Russell, W2DMR. THE ELECTROMAGNETIC WAVE. GENERATION OF AN EM WAVE. E field. Current flow. H field. Antenna. DISTANCE SQUARED. MODES OF TRANSMISSION. - PowerPoint PPT PresentationTRANSCRIPT
HOW DOES MY SIGNAL GET FROM HERE TO THERE?
By Forest Cummings, W5LQUAnd Dave Russell, W2DMR
THE ELECTROMAGNETIC WAVE
GENERATION OF AN EM WAVE
E field
H field
Antenna
Current flow
DISTANCE SQUARED
MODES OF TRANSMISSION
Line of sight
Ground Wave – low frequencies
Reflections – most important for HF
Special Cases – scatter, ducting
IONOSPHERIC LAYERS
The D layer (50mi) is an absorption layer affecting frequencies from 1.8 MHz to 7 MHz.
The E layer (70mi) is a sporadic layer with some very interesting effects.
The F layers are the most Important for HF bands long range communication.
Are created by the UV and X-ray radiation from the sun.
ELECTRON DENSITIESVariations in the ionosphere electron densities occur for several reasons:
Day and night
Summer and Winter
The 11 year solar sunspot cycle
Solar storms
IONOSPHERIC REFRACTION
IONOSHERIC SKIP ZONES
MAXIMUM USEABLE FREQ The maximum useable frequency is the highest
frequency that can be refracted by the ionospheric layer
This is commonly called the MUF
Frequencies higher than the MUF will penetrate the Ionosphere and will escape into space
It is best to choose a frequency just below the MUF
PROPAGATION CHART
Propagation Charts are madefor certain paths and specificdates and time periods.
They show the variations of the MUF during a 24 hour period
AZIMUTHAL MAP
If you have a directional antenna it is not intuitive to really know exactly which direction to point it to reach the desired target area.
This Azimuthal Map shows directions to the world from Dallas, Texas.
SUNSPOT CYCLES
This chart is from the January 2005 QST
Maunder minimumAD 1645 - 1715
SUNSPOT CYCLE 23
GEOMAGNETIC ACTIVITY
TROPOSPHERIC SCATTER
DUCTING
PROPOGATION CHART
RECEIVER NOISEThe last link in the communications path is the receiver and
conditions at the receiver location. Noise at the receive site
is the primary limitation.
290 K
+40 dB
10 MHz 20 MHz
20 dB/octave
20 dB/decade
200 MHz
Man MadeGalactic
NOISE LEVELS VS FREQUENCY
Thermal
MF (300Hz – 3MHz)
HF (3 – 30 MHz)80 meters (3.5 – 4.0 MHz)Similar to 160mD layer absorption not quite as bad as 160m Some E layer skip in the daytimeHigh manmade and atmospheric noisePretty good ground wave coverage – 40 milesWorldwide night time coverage – F2 layer
160 meters (1.8 – 2.0 MHz)High D layer absorptionGood ground wave coverage – up to 90 milesHigh manmade and atmospheric noiseWorldwide night time coverage – F2 layer
HF (3 – 30 MHz) 140 Meters (7.0 – 7.3 MHz)Mild D layer absorptionNoise levels lowerDefined daytime skip zoneShort skip on E and F layersWorldwide night time coverage even at Solar minimum – F2 layer
30 meters (10.1 – 10.15 MHz) CW onlyD layer not significantGenerally open 24 hours for F2 layer coverageGood throughout the Solar cycle
HF (3 – 30 MHZ) 220 meters (14.0 – 14.35MHz)Primary long haul DX bandF2 layer propagation during the dayMay stay open all night at Solar maximumLow atmospheric noise and some E layer short skipMost popular but crowded Band
17 meters (18.068 – 18.168 MHz)Very similar to 20 metersSolar effects more pronouncedMostly daytime and early eveningNot usually as crowded as 20 meters
HF (3 – 30 MHZ) 315 meters (21.0 – 21.45 MHz)Primary DX band at Solar maximumSensitive to changing Solar activityBasically daytime, but early night at Solar maximumOnly some sporadic E at Solar minimum
12 meters (24.89 – 24.99 MHz)Open only during moderate to high Solar activitySome sporadic E in late spring and summer
HF (3 – 30 MHZ) 4 / VHF10 meters (28.0 – 29.6 MHz)Extreme variations in propagation modesVery efficient F2 propagation at Solar maximum with low powerSingle and multiple hop propagationOpen sunrise to few hours past sunsetNo propagation at Solar minimum except sporadic E, aurora, meteor scatter
6 meters (50.0 – 54.0 MHz) “The Magic Band” really VHF (30 – 300MHz)World wide daylight DX at Solar maximumSporadic E is most common and popular modeRegular tropospheric scatterAuroral propagation in afternoons when Solar magnetic activityDucting is rare
VHF (30 – 300MHZ) 2 meters (144 – 148 MHz)No F propagationLine of sight dependent on antenna heightSome sporadic E similar to 6 metersTropospheric scatter and ducting up to 500 milesAuroral and meteor scatter
135 cm (222 – 225 MHz)Nearly as good as 2 metersSporadic E is rare
UHF (300 3000 MHZ) 70 cm (420 – 450 MHz)Line of sight dependent on height of antennasNo sporadic E, but some Auroral scatterTropospheric scatter and ducting is good
33 cm (902 – 928 MHz) and higherNo ionospheric modes of propagationLine of sight dependent on height of antennaHigh gain antennasAuroral and Tropospheric scatterVery sensitive to changes in weather
IN CONCLUSION
LISTEN A LOTGet acquainted with the bands, and the variation in propagation conditionsdue to weather, day/night, seasonal, and Solar activity. But, above all;
ENJOY HAM RADIOAND
HAVE FUN !