GB1328595A - Carrier frequency telecommunications systems - Google Patents

Abstract

1328595 Radio signalling SIEMENS AG 23 Aug 1971 [25 Aug 1970] 39360/71 Heading H4L In a carrier frequency telecommunication system in which a plurality of different frequency carrier waves are available and means are provided at each station for selecting the carrier wave giving the best results, the receiver of each station in its inoperative condition scans the frequency positions of the carrier in a predetermined sequence and the transmitter at the calling station automatically transmits a synchronizing signal at each frequency position in the same sequence which is followed by a test signal which may contain the address of the called station at each frequency position in the sequence. When the receiver at the called station detects the sync. signal at one of the frequency positions it is automatically synchronized and it then analyses the sequence of test signals to determine the quality at the respective frequency positions. When the best carrier wave frequency has been determined the called station transmits back a test signal at each frequency position in the sequence which includes identification of the frequency providing the best signal, and this frequency is then used by the calling station transmitter. At the calling station the test signals are similarly analysed to determine the best frequency for the return direction and this information is automatically transmitted to the called station. During normal transmission, if the quality of the transmission goes below a predetermined limit, the transmission is interrupted and hunting for the best frequency position commences. The quality of the transmission may be measured by the means disclosed in Specification 1,328,594.