(19)

(11)

EP 0 327 617 A1

(12)

(43) Date of publication: 16.08.1989 Bulletin 1989/33 (21) Application number: 88905991.0 (22) Date of filing: 20.07.1988

(51) International Patent Classification (IPC):  G10K 11/ 16( . ) H04R 3/ 00( . ) G10K 11/ 178( . ) (86) International application number: PCT/GB1988/000581 (87) International publication number: WO 1989/000746 (26.01.1989 Gazette 1989/03)

(84) Designated Contracting States: AT BE CH DE FR GB IT LI LU NL SE (30) Priority: 20.07.1987 GB 19870017043 20.07.1987 GB 19870017040 20.07.1987 GB 19870017042 (71) Applicant: PLESSEY OVERSEAS LIMITED Ilford Essex IG1 4AQ (GB)	(72) Inventors: TWINEY, Robert, Christopher Northampton NN4 9BA (GB) SALLOWAY, Anthony, John Northampton NN3 3RW (GB) (74) Representative: Lupton, Frederick  The Plessey Company plc Intellectual Property Dept. Vicarage Lane Ilford, Essex IG1 4AQ Ilford, Essex IG1 4AQ (GB)