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.
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 made for certain paths and specific dates 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 minimum AD 1645 - 1715
RECEIVER NOISE The 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 MHz20 MHz 20 dB/octave 20 dB/decade 200 MHz Man Made Galactic NOISE LEVELS VS FREQUENCY Thermal
MF (300Hz – 3MHz) HF (3 – 30 MHz) 80 meters (3.5 – 4.0 MHz) Similar to 160m D layer absorption not quite as bad as 160m Some E layer skip in the daytime High manmade and atmospheric noise Pretty good ground wave coverage – 40 miles Worldwide night time coverage – F2 layer 160 meters (1.8 – 2.0 MHz) High D layer absorption Good ground wave coverage – up to 90 miles High manmade and atmospheric noise Worldwide night time coverage – F2 layer
HF (3 – 30 MHz) 1 40 Meters (7.0 – 7.3 MHz) Mild D layer absorption Noise levels lower Defined daytime skip zone Short skip on E and F layers Worldwide night time coverage even at Solar minimum – F2 layer 30 meters (10.1 – 10.15 MHz) CW only D layer not significant Generally open 24 hours for F2 layer coverage Good throughout the Solar cycle
HF (3 – 30 MHZ) 2 20 meters (14.0 – 14.35MHz) Primary long haul DX band F2 layer propagation during the day May stay open all night at Solar maximum Low atmospheric noise and some E layer short skip Most popular but crowded Band 17 meters (18.068 – 18.168 MHz) Very similar to 20 meters Solar effects more pronounced Mostly daytime and early evening Not usually as crowded as 20 meters
HF (3 – 30 MHZ) 3 15 meters (21.0 – 21.45 MHz) Primary DX band at Solar maximum Sensitive to changing Solar activity Basically daytime, but early night at Solar maximum Only some sporadic E at Solar minimum 12 meters (24.89 – 24.99 MHz) Open only during moderate to high Solar activity Some sporadic E in late spring and summer
HF (3 – 30 MHZ) 4 / VHF 10 meters (28.0 – 29.6 MHz) Extreme variations in propagation modes Very efficient F2 propagation at Solar maximum with low power Single and multiple hop propagation Open sunrise to few hours past sunset No 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 maximum Sporadic E is most common and popular mode Regular tropospheric scatter Auroral propagation in afternoons when Solar magnetic activity Ducting is rare
VHF (30 – 300MHZ) 2 meters (144 – 148 MHz) No F propagation Line of sight dependent on antenna height Some sporadic E similar to 6 meters Tropospheric scatter and ducting up to 500 miles Auroral and meteor scatter 135 cm (222 – 225 MHz) Nearly as good as 2 meters Sporadic E is rare
UHF (300 3000 MHZ) 70 cm (420 – 450 MHz) Line of sight dependent on height of antennas No sporadic E, but some Auroral scatter Tropospheric scatter and ducting is good 33 cm (902 – 928 MHz) and higher No ionospheric modes of propagation Line of sight dependent on height of antenna High gain antennas Auroral and Tropospheric scatter Very sensitive to changes in weather
IN CONCLUSION LISTEN A LOT Get acquainted with the bands, and the variation in propagation conditions due to weather, day/night, seasonal, and Solar activity. But, above all; ENJOY HAM RADIO AND HAVE FUN !