The Wireless Telegraphy Regulations originating in 1905(!) and in force up till 1980 had provisions re secrecy, and is no doubt the source of "rules" originally published in the various radiocommunications licensing schemes (amateur radio service, marine etc.). Copy below to bring back fond memories to some
Those Regulations were subsequently incorporated into a variety of acts including the Telecommunications (Interception and Access) Act, Privacy Act etc. and in these the requirements for privacy tend to be specific e.g. the privacy of phone calls, electronic messaging etc. and personal information.
In short, if something is transmitted by radio of a general nature and not being matters covered by the telecommunications or privacy acts I don't believe any secrecy applies, hence the streaming of airband, marine, emergency services communications etc. despite what the originators might like. As a result, police and some other services have moved to using encryption, taking their own steps to preserve the secrecy and privacy of their communications.
However I stand to be corrected, if someone can point to a specific
current act or regulation
WIRELESS TELEGRAPHY REGULATIONS - SECT. 36.
Provisions as to secrecy
36. (1) Any person operating an authorized station or having access to wireless messages transmitted or received by an authorized station shall make, in accordance with a form approved by the Minister, a declaration that he will preserve the secrecy of all commercial, naval, military or air force wireless messages transmitted or received by that station.
(2) The licensee of an authorized station shall take such steps as are necessary to ensure the secrecy of wireless communications transmitted or received by the station.
(3) A person shall not, without lawful authority, divulge, or make any use whatsoever of, any portion of the text of any message transmitted or received by any station whether situated in Australia or elsewhere, or disclose in any manner whatsoever the existence of any such message.