Geelong residents could be permanently barred from receiving Melbourne digital radio signals after a push by Geelong commercial stations for state-of-the-art jamming technology to block Melbourne broadcasts. Since May, Geelong listeners have been tapping into powerful digital broadcasts beamed from Melbourne's Mount Dandenong. But in a move designed to protect the market share of Geelong heavy hitters Bay-FM, The Pulse and K-Rock, executives have been lobbying to save their stations' audience share and revenue. Under Federal Government legislation, the Australian radio market is divided into licence areas that protect commercial operators from rivals in adjacent markets. But signals often "spill-over" into unintended areas. Geelong, located just 75 kilometres from the Melbourne CBD, is a prime case. Since digital radio was switched on, Geelong residents with digital receivers have been able to access new features, including real-time track listings, as well as services provided by ABC and SBS. Melbourne analogue signals have always spilled-over into Geelong -- the proposed jammer could not only cut-off digital signals, but if analogue radio is switched off, neuter the reception of Melbourne radio altogether. Currently, there are no government plans to introduce digital radio in Geelong, or anywhere else outside the major capital cities. The Australian Communications and Media Authority is set to rule on a licence for the jammer but has so far remained mute. SBS, who transmits on a separate spectrum to the commercial and community operators, has slammed the proposal, claiming its installation would contradict Australia's obligations under international telecommunication regulations. Peak body Commercial Radio Australia says the costs of the proposed jammer will be born by the Geelong commercials. But the installation of expensive "in-fill" technology to boost the jammed signal in areas abutting the Geelong licence area in Melbourne's west could be born by commercial stations in Melbourne. Projected sites for "in-fill" transmitters are said to include the Bolte Bridge and the Como Hotel in South Yarra. The Melbourne stations would be effectively paying for their signals to be restricted. Crikey can also reveal that steps to limit spillover from the Melbourne licence area into Geelong are already afoot. Sources say digital reception in Melbourne's west has been dulled by a "notch" woven in to the broadcast from Mount Dandenong, with digital reception in Melbourne suburbs like Werribee and Hoppers Crossing known to be "sub-optimal". The Geelong jamming proposal would only apply to commercial and community signals, with the SBS and ABC operating on a separate multiplex. If the jammer is approved, Geelong listeners could find themselves in a curious situation where they are able to tune into ABC and SBS digital but not commercial or community stations -- this means, for instance, that SBS's multiligual programming could be heard in Geelong, but not 3ZZZ's, or Triple J's new station could be heard, but not Triple R's. Both the ABC and SBS are keen to keep all radio signals on the same footing, and have expressed hostility over a two-tiered system in Geelong. They say the jammer could result in higher costs for Melbourne stations and less listening options for Geelong residents, who famously maintain a love-hate relationship with their Melbourne counterparts. Commercial radio is already preparing for the installation of the jammer, with Commercial Radio Australia chief Joan Warner telling the Geelong Advertiser last week that Geelong's current digital reception was "fortuitous". Warner told Crikey the decision to implement the "coverage management system" is only in its preliminary stages and that the major costs would be born by the Geelong commercial stations. There were several options on the table, Warner said. Warner said that if residents want unfettered access to Melbourne radio, they should lobby the government to change the licensing regime. Disclaimer: The author serves on the board of non-digital youth broadcaster SYN FM.