The modems we use are industry standard units manufactured by well established suppliers such as RF Datatech, SATEL, and GE. Typical frequencies are in the region of 400 to 500 MHz, which includes licence free bands in the UK and certain other countries. The key advantages of these frequencies are:
- comparatively few problems with link drop-out
- good range, far greater than can be achieved at the higher frequencies
So long as there is a line of sight, and the remote station is within the horizon distance (readily calculated from a knowledge of the antenna heights amsl and the radius of the Earth), it is usually possible to maintain reliable communications.
The baud rate used is typically 9600, and the SSSCP protocol has been written using binary encoding to compress data and maximise reliability.