PROPAGATION OF ELECTROMAGNETIC WAVES

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 !