What is Skip?
CB radio was intended to be a short range communications service.
Normally CB radio transmissions are line of site.
The frequencies on which it operates have some interesting propagation characteristics.
Your CB signal goes up as well as out and away from your antenna.
When the conditions are just right it is possible to bounce the radio signal off the atmosphere and it will land hundreds of miles away.
Frequencies are able to be refracted by the existence of highly charged particles in the ionosphere.
This bouncing of a signal off the ionosphere is called skywave propagation or shooting skip.
With this ability to shoot skip, CBers have been able to communicate thousands of miles and sometimes around the world.
The ability of the ionosphere to refract signals back to earth is related to the amount of ionization possible do to the 11-year sunspot cycle.
In times of high sunspot activity the band can remain open to much of the world for long periods of time.
In years of low sunspot activity it may not be possible to shoot skip at all.
Therefore its not impossible for someone using a CB in Oregon to communicate with another person in Florida.
What is the Ionosphere?
The ionosphere is a region of the upper atmosphere where neutral air is ionized by solar photons and cosmic rays.
When radio waves reach the ionosphere at a shallow angle they are partly reflected by the surface.
Different frequencies are reflected by different amounts.
The condition of the ionosphere is constantly changing due to interaction with incoming radiation.
When signals have reflected off this irregular surface, they may fade in and out.
Depending on the antenna, the signals may reach the ionosphere at a steep angle and be reflected almost straight down.
An antenna may aim the signal at the horizon, like using a horizontal beam antenna, and the signal may reach the ionosphere at a shallow angle and return to earth a great distance away.
The Earth's surface may in return reflect the incoming wave back toward the ionosphere again.
As a result, like a rock skipping across a pond, the signal may actually bounce between the earth and ionosphere multiple times.
This phenomenon is known as multihop propagation.
Signals of only a few watts can sometimes be received thousands of miles away as a result.
Frequencies below 10 MHz travel most efficiently by skywave at night.
Frequencies above 10 MHz travel better during the day.
The maximum usable frequency for skywave propagation is strongly influenced by sunspot numbers.
This leads to an increase in the skip distance of the skywave at night.
FCC Regulations
Taking advantage of this skip to communicate with those hundreds of miles away is discouraged by the FCC.
Currently this practice is considered to be illegal as per Part 95, Subpart D of the FCC rules.
"It is illegal to engage in, or attempt to engage in communications with any
station more than 155.3 miles from your location"
This makes it impossible for CB operators who wish to shoot skip to remain in compliance with FCC regulations.
The intent behind this restriction is regarded as an effort to keep CB as a local service only.