| >> Ground-wave
which travels directly from the transmitting antenna to the receiving antenna following the contours of the earth.
Generally speaking, ground-wave is used to communicate over shorter distances usually less than 50km. Because ground-wave follows the contours of the earth, it is affected by the type of terrain it passes over. Ground-wave is rapidly reduced in level when it passes over heavily forested areas or mountainous terrain.
| >> Sky-wave
which travels upward and at an angle from the antenna, until it reaches the ionosphere (an ionised layer high above the earth's surface) and is refracted back down to earth, to the receiving antenna.
Sky-wave is used to communicate reliably over medium to long distances up to 3,000km. Whilst the nature of sky-wave propagation means it is not affected by the type of terrain as in ground-waves it is affected by factors involving the ionosphere as described below.
| >> Frequency selection
is perhaps the most important factor that will determine the success of your HF/SSB communications.
Generally speaking the greater the distance over which you want to communicate, the higher the frequency you should use.
Beacon Call, a Selcall (selective call) function built into the Barrett 2000 series transceiver, makes finding the correct frequency to use easy. Beacon call is based on the network transceivers all having a selection of frequencies that will accommodate most ionospheric conditions. When in standby the network transceivers scan these frequencies waiting for a call (Selcall or Beacon Call) from another transceiver.
The transceiver wishing to check for the best frequency to operate on sends a Beacon Call to the station he wishes to contact. If his call to the other station is successful he will hear a revertive call from the station he is calling, indicating the channel he selected was suitable for the ionospheric conditions prevailing. If he does not hear this revertive call or it is very weak, he tries on another channel until a revertive call of a satisfactory signal strength is heard.
| >> Time of day
As a rule, the higher the sun, the higher the frequency that should be used. This means that you will generally use a low frequency to communicate early morning, late afternoon and evening, but you will use a higher frequency to cover the same distance during times when the sun is high in the sky (e.g. midday).
You will need to observe the above rule carefully if your transceiver has a limited number of frequencies programmed into it, as you may only be able to communicate effectively at certain times of the day.
| >> Weather conditions
Certain weather conditions will also affect HF/SSB communications. Stormy conditions will increase the background noise as a result of 'static' caused by lightning.
This background noise could rise to a level that will blank out the signals you are trying to receive.
| >> Man-made electrical interference
Interference of an electrical nature can be caused by overhanging power lines, high power generators, air-conditioners, thermostats, refrigerators and vehicle engines, when in close proximity to your antenna.
The result of such interference may cause a continuous or intermittent increase in the level of background noise.