IMPROVEMENTS IN MULTICOUPLER SYSTEMS

Abstract: A multicoupler circuit (12) for use in communication sys­ tems to couple each of a plurality of transceivers (10, 17) oper­ ating at differing RF frequencies to a common aerial (16), wherein the conventionally used single frequency tuning multi­ coupler for at least one channel is replaced by a broad bandpass filter (18).

Description: Title: Improvements in Multicoupler Systems Field of the Invention This invention relates to a multicoupler system. A multicoupler, as the term is conventionally used herein, means a coupler in the field of communications systems for coupling each one of a plurality of transmitter/receivers (transceivers) operating at differing R.F. frequencies to a common aerial. Background to the Invention In the field of communications it is commonly desired for any one of a plurality of stations to be able to intercommunicate with any one or more of the other stations, with as many communications channels open at the same time as is required, and without interference between simultaneously open channels. Each channel therefore has an allotted R.F. carrier frequency, and each station has a bank of transceivers which can be simultaneously operational in different channels of communication. This would normally mean that each station should be equipped with a corresponding bank of aerials, each individually matched to suit transmission and reception on a given communications channel. A multicoupler system, as exemplified by Figure 1, enables a single aerial to be employed at each station for a multiple channel communications system of the type described above, which is, for example, commonly employed to enable intercommunication between ships of a fleet, possibly together with one or more land stations. Increasingly, moreover, it is desired for such a communications system to be at least partially protected against jamming or, less importantly, against eavesdropping. Such protection can be afforded by frequency hopping. With frequency hopping, the R.F. carrier frequency is repetitively changed, for example ten to fifteen times a second, in accordance with a pre-arranged frequency plan which is followed at both ends of a communications channel. At the present time, however, a multicoupler system, which incorporates single frequency tuning circuits, prohibits the use of frequency hopping. The Invention According to the invention, a multicoupler system is provided which has an allotted R.F. frequency range for at least one channel, which frequency range does not overlap the R.F. frequency range within which other channels are operational, and the single frequency tuning multicoupler for said at least one channel is replaced by a broad bandpass filter. The invention thereby allows the transceiver connected to such broad bandpass filter multicoupler to operate with frequency hopping, within the allotted frequency range from which operation of the other channels is precluded. Typically, for example, a conventional multicoupler system has channels which can be operational each anywhere in the 225 to 400 MHz (UHF) frequency range. In accordance with the invention, one channel may be restricted to frequency hopping within the range of a broad bandpass filter from 360 to 400 MHz, and the operation of the other channels is excluded from this latter range. In some circumstances, it will also be possible to replace the single frequency tuning multicoupler in at least one further channel by a broad bandpass filter multicoupler covering a different 40 MHz range, excluding operation of the remaining channels from the two or more broad bandpass ranges. The multicoupler system of this invention enables slow frequency hopping, typically 10 to 15 changes per second, or frequency hopping at a substantially faster rate, in at least one channel. Description of drawings In the accompanying drawings: Figure 1 shows the circuit diagram of a conventional multicoupler system Figure 2 shows the circuit diagram of a modified multicoupler system in accordance with this invention, in similar diagrammatic manner; and Figure 3 diagrammatically illustrates in plan the construction of a broad bandpass filter installed in a multicoupler, in accordance with the present invention. Description of the embodiment In the conventional multicoupler circuit of Figure 1, a plurality of UHF transceivers are referred 10A, lOB the multicoupler system is referenced 12 and the single frequency tuning multicouplers therein, any one operational in the range 225 to 400 MHz, are referenced 12A, 12B .... Each multicoupler 12A, 12B .... incorporates a T-coupler which connects the corresponding tuning circuit thereof to a common aerial line leading to a single aerial 16. In the modified multicoupler circuit in accordance with the invention, shown in Figure 2, UHF transceiver lOD is replaced by a transceiver 17 which performs frequency hopping, in accordance with a frequency plan, in the range 360 to 400 MHz. The single frequency tuning multicoupler 12D is replaced by a broad bandpass filter multicoupler 18 covering the range 360 to 400 MHz, whilst operation of the transceivers 10A, lOB, lOC is now restricted to lie within the range 225 to 360 MHz. The common aerial connection and single aerial are again respectively referenced 14 and 16. Figure 3 shows a practical construction of the broad bandpass filter multicoupler 18 incorporated in the multicoupler cabinet 20. The cabinet 20 has a plurality of "drawers for the usual single frequency tuners, and the broad bandpass filter multicoupler 18 takes the form of a substitute "drawer". More particularly, the broad bandpass filter in the multicoupler 18 comprises a copper box 22 with screwadjustable trimmers 24 used for initial setting up of one filter, and with an input/output 26 to and from the transceiver. An aerial connector 28 couples to a standard T-coupler 30, which is equipped with a geared manual adjustment device 32. The broad bandpass filter multicoupler 18 enables access for an "agile" (frequency hopping) tranceiver on to an aerial common to a plurality of channels of communication.

Claims: Claims 1. A multicoupler system which has an allotted RF frequency range for at least one channel, which frequency range does not overlap the RF frequency range within which the other channels are operational, characterised in that the conventional multicoupler for said at least one channel is replaced by a broad bandpass filter (18). 2. A system according to claim 1, characterised by combination with a transceiver connected to the broad bandpass filter for said at least one channel to operate with frequency hopping within an allotted frequency range from which operation of the other channels is precluded. 3. A system according to claim 2, characterised in that the broad bandpass filter covers a predetermined frequency range of about 40MHz. 4. A system according to claim 1 or claim 2, having channels operational each anywhere in the 225 to 400MHz frequency range, characterised in that one channel is restricted to frequency hopping within the range of a broad bandpass filter from 360 to 400MHz, and the operation of the other channels is excluded from this latter frequency range. 5. A system according to any of claims 1 to 4, characterised in that the multicoupler for at least one further channel is constituted by a broad band pass filter. 6. A system according to claim 5 when appendant to claim 3 or claim 4, characterised in that the broad bandpass filter for said further channel covers a frequency range of about 40MHz differing from and not overlapping the range covered by the first. 7. A system according to any of claims 1 to 5, characterised by slow frequency hopping of the order of 10 to 15 changes per second. 8,. A system according to any of claims 1 to 5, characterised by fast frequency hopping exceeding 15 changes per second in at least one channel.

Inventors: MASON, HAROLD PETER, ROLFE, STEPHEN KENNETH
Applicants: AIRTECH LIMITED
Application year: 1985
Main classification: H04B1
IPC codes: H03H7, H04B1