The automatic protection switching system of TH radio

It is the purpose of the automatic protection switching system to ensure continuity of service over the TH system. The protection system prevents any signal loss from occurring in case of fading, and it will restore service a short time after transmission equipment has failed. The over-all reliability of the TH system is thereby very substantially improved. Switching is done in switching sections. These usually contain a number of repeater stations, in which case the switching is normally done at IF. When a channel has to be switched, it is replaced over the full length of the switching section by a protection channel. Protection is also provided for FM terminal transmitters and receivers; in this case the switch is at IF on one side and at baseband on the other. In addition to the IF and baseband switches themselves, the system comprises monitors of various sorts, logic circuitry at each end of the switching section, communication facilities between ends over the auxiliary radio channel, and manual controls. In contrast to the rest of the TH system, which uses mostly electron tubes, the switching system employs solid-state devices entirely.