Follow our tweets!

Home
Lost Reg Code?
News
Online KiwiSDRs
macOS Software
Windows Software
Ham Radio iPhone/iPad
Linux Software
Support/FAQ
Update Policy

USB Icom CI-V Interface

Radio Hobbyist Products
  22m Programmable Beacon Kit
  22m Part 15 Beacon Kit
  CW Keyer For Beacons Kit
  Jellyfish Transformer
  Cyclops Antenna Transformer

General Interest Programs
  Atomic Mac/PC
  Audiocorder
  Audio Toolbox
  Black Cat Timer
  Diet Sleuth
  iUnit
  Graffikon
  Graph Paper Maker
  Health Tracker
  Image Resizer
  Knitting Wizard
  Label Wizard
  Prog Audio Gen
  Sound Byte
  Synth 76477

Amateur Radio Programs
  AirSpyHF+ Server
  Audiocorder
  Black Cat Absolute ACARS
  Black Cat ACARS
  Black Cat ALE
  Black Cat ALE Vacuum Cleaner
  Black Cat NetFinder
  Black Cat GMDSS
  Black Cat HF Fax
  Black Cat SSTV
  Black Cat NAVTEX SITOR-B
  Carrier Sleuth
  Cocoa 1090
  Cocoa RTL Server
  DGPS Decoding
  DX Toolbox
  Elmer
  eQSL Factory
  MatchMaker
  KiwiKonnect
  KiwiSDR Monitor
  KiwiSDR Sound Client
  MININEC Pro
  Morse Mania
  MultiMode
  sdrRewind
  RF Toolbox
  SDRuno Plugin
  SDRuno Equalizer Plugin
  SelCall
  Sonde

iPhone/iPad Apps
  ALE
  Atoms To Go
  dB Calc
  Clik Trak
  DGPS Decoder
  Drill Calc
  DX Toolbox
  Elmer Extra
  Elmer General
  Elmer Tech
  Feld Hellschreiber
  Field Strength Calc
  Function Generator Pad
  GMDSS
  Godafoss
  HF Weather Fax
  iAttenuate
  iFunctionGenerator
  iSoundex
  iSoundByte
  iSweep
  iUnit
  Morse Mania
  ACARS Pad
  Morse Pad
  NAVTEX Pad
  Packet Pad
  PSK31 Pad
  SSTV Pad
  Photon Calc
  Rad Map Tracker
  RF Link Calc
  SelCall Tone Gen
  Sound Byte
  Sound Byte Control
  Spectrum Pad
  SWBC Schedules
  Synth 76477
  Synth Motion
  Transmission Line Calc
  Weather Calc
  Wire Calc

iPhone/iPad Bundles
  RF Calculator Apps
  Ham Radio Decoder Apps
  Audio Utility Apps
  Shortwave Weather Apps
  Ham Radio Exam Study Apps
  Shortwave Decoder Apps

Android Apps
  ACARS
  Audio Function Generator
  Audio Spectrum Analyzer
  DGPS Decoder
  HF Weather Fax
  NAVTEX
  Rad Map Tracker
  SelCall Tone Gen
  Sound Byte Control
  SWBC Schedules
  Wire Calc

About Black Cat Systems
Site Map
Our software for Mac OSX
Privacy Policy
Press/Media
HFunderground
Apple /// Emulator

Macintosh Links
Shortwave Radio
Pirate Radio
Spy Numbers Stations
Science and Electronics
Ham Radio Software

HF Shortwave Radio Propagation - Basics

Shortwave (HF) propagation is possible due to the ionosphere, a region of the upper atmosphere ranging from approximately 60 to 450 km in height.

The ionosphere is divided up into three regions, the D, E, and F layers, with the F layer subdivided into the F1 and F2 layers.

The gas molecules in the ionosphere are ionized due to radiation from the Sun. That is, they are stripped of some of their electrons. These regions with free electrons can reflect radio waves back to the earth. This ionization occurs during the daytime. At night, the ions start to recombine back into neutral molecules. The D and E layers completely recombine at night, the F layer only partially recombines. This allows HF propagation to continue at night.

Only certain frequency ranges of radio waves (often called shortwave) can be reflected. Those which are too high in frequency pass through the ionosphere. Those which are too low in frequency are absorbed before they can be reflected. Generally, the HF or shortwave spectrum is the range from around 2 to 30 MHz. Under times of very high solar activity, even higher frequency can sometimes be reflected, while under times of low activity, the maximum frequency can be much lower, sometimes only 10 or 15 MHz at best.

D Layer

The D layer is the lowest layer of the ionosphere, and the least ionized. It does not reflect radio waves, but it does absorb and attenuate them. It only exists during the daytime. The higher the solar activity, the more attenuation caused by the D layer. Hence, the D layer can be thought of as setting the lowest frequency that can be propagated over a certain path, based on the transmitter power levels, and current solar activity levels.

E Layer

The E layer also exists only during the daytime, except for so called "Sporadic E" which can occur anytime. Generally, the ionization of the E layer is insufficient to reflect radio waves, except for Sporadic E, which has a much higher ionization level. Sporadic E is generally caused more by weather conditions than solar activity.

F Layer

The F layer builds up during the daytime, under the effect of radiation from the Sun. It starts to recombine slowly at nightime, but never completely recombines, hence it is available 24 hours a day for reflecting radio waves. The ionization levels vary during the day of course so that higher frequencies tend to propagate better when their path is in sunlight.

The F layer is responsible for essentially all of the shortwave radio proagation we have. Radio waves that strike it at the correct angle are reflected back to the earth. The range that can be covered with one such reflection (or hop) varies with the frequency, solar conditions, radiation angle, etc. but is generally a few thousand km at most.

To cover further distances, multiple hops are required, each one of course results in a lower signal level. As a result, the strongest signal conditions generally occur when the highest possible frequency for a given path is used, since that requires in the fewest hops.

[Table of Contents]
Previous [Table of Contents]
Next [Solar Flux]