| 摘要 |
PCT No. PCT/GB86/00762 Sec. 371 Date Jun. 2, 1988 Sec. 102(e) Date Jun. 2, 1988 PCT Filed Dec. 15, 1986 PCT Pub. No. WO87/03501 PCT Pub. Date Jun. 18, 1987.An audio signal and a selected one of a plurality of sub-audio tones are transmitted to a plurality of receiving each being capable of being conditioned by first, second or third selected sub-audio tones so that either all receivers, or only a select group of all of the receivers or only an intended group are the receivers accept the transmitted audio signal, there being as many selectable second sub-audio signals as there are groups and as many selectable third sub-audio signals as there are receivers. |
