Radio Wave Propagation

Introduction

Radio Wave Propagation — ground wave, sky wave, ionospheric layers, MUF, solar activity, sporadic-E, and scatter propagation

Ground Wave — follows Earth surface, most effective at MF and lower HF (such as 160 m and 80 m)
Sky Wave — reflects off ionosphere back to Earth, enables long-distance communication on HF

Ionosphere — region of upper atmosphere from 60 to 600 km ionized by solar UV and X-ray radiation
Ionospheric Layers — D, E, and F layers; D absorbs lower HF by day and disappears at night

Skip Distance — minimum distance from transmitter where sky wave returns to Earth
Skip Distance Factors — greatest when MUF is just above the operating frequency; higher MUF means shorter skip for a fixed frequency; multi-hop extends range

MUF — Maximum Usable Frequency, the highest frequency that returns to Earth via sky wave at a given angle
MUF Variation — varies with ionization, at solar maximum MUF can reach 30 MHz or more, check by listening for signals on the band

D-Layer Absorption — absorbs lower HF by day, 160 and 80 metres have no long-distance sky wave during daylight
Fading — signal strength variation caused by multi-path, multiple signal paths arriving at different times

Sunspots — dark regions indicating high solar magnetic activity, more sunspots mean more ionization and better HF
Solar Cycle — approximately 11 years, solar maximum gives high MUF and good DX on high bands, solar minimum gives lower MUF and better low bands

Sporadic-E — patches of intense E-layer ionization that enable VHF skip on 6 metres and sometimes 2 metres
Tropospheric Ducting — VHF and UHF signals trapped in temperature inversion layer, extends range beyond line of sight

Scatter Propagation — small fraction of signal scattered by irregularities in the ionosphere or troposphere, weak but usable

Ground Wave — follows Earth surface, best on low HF, limited range. Sky wave refracted by ionosphere for DX. Line of sight primary on VHF and above
Ionosphere Layers — D absorbs day only, E occasional 6 metre skip, F1 and F2 for HF DX, F2 most important
Skip Zone — dead zone between ground wave limit and sky wave first return point. Lower radiation angle produces longer skip distance.
MUF and LUF — MUF is highest frequency returning to Earth, LUF is lowest usable before D-layer absorption, listen for signals to check MUF
D Layer and Fading — D layer absorbs lower HF by day, fading from multi-path, SID from solar flare shuts down HF for minutes to hours
Sunspots and Solar Cycle — sunspots increase solar radiation, raise MUF, improve HF. 11-year cycle with solar max opening high bands
Sporadic-E and Tropospheric Ducting — Es provides VHF skip on 6 metres, tropospheric ducting extends VHF and UHF range
Scatter Propagation — weak signals heard in skip zone, works above MUF, includes auroral scatter on VHF with distorted signal