it is a channel modification.
the normal CB 40 channels go from 26.965 (ch.1) to 27.405 (ch.40).
during the hayday of cb radio these channels became constantly crowded when the skip was rolling and so people began to venture above and below the normal 40 channels in search of some quieter frequencies.
there are still people using these freqs to this day.
the frequencies below channel 1 are generally AM operators, and the freqs above channel 40 are generally SSB operators.
to find out what frequencies you have, we will need to take the top and bottom covers off of your radio.
this is not difficult and wont mess anything up as long as you promise yourself beforehand that you're not going to mess with anything in there. LOL
when you take the top cover off, look for the largest IC chip on the board, and post the numbers that are on it.
they will either be UPD858 or MB8719.
when you take the bottom cover off, you will notice some wires going to this chip on the solder (green) side of the board.
these wires will run to either your PA or NB switch, or both.
some good closeup pics of these areas will help alot in determining exactly what mod was done, and that will allow us to find out what freq range you have when you push the switch in.
LC