Impact on England 'stops Welsh news' on Radio 1 and 2
The potential impact on some listeners in England has prevented Welsh news bulletins on BBC Radios 1 and 2.
A senior BBC Wales manager has told a committee of assembly members that signal overlaps into Somerset and north-west England from Wales-based FM transmitters had halted the plan.
Rhys Evans said new broadcasting technologies, including 5G, may mean the idea will be implemented in future.
The assembly culture committee is holding an inquiry into radio.
An assembly report published in 2017 recommended Wales-based news bulletins were included on popular BBC radio stations to ensure Welsh listeners heard news that was relevant to them.
BBC Director General Tony Hall said the idea would be investigated during an appearance before the same committee in 2016.
Mr Evans said the BBC had worked for many months to try and get a solution.
But he told AMs that one transmitter at Wenvoe in the Vale of Glamorgan, "blasts an FM signal out across the whole of south Wales, as well as the south-west of England".
"It is not possible to opt out within FM because there is very little FM frequency available," he said.
"That said, the concept is still a valid one and is still a concept that...when technologies change, particularly 5G technologies, I think there will be the possibility to revisit that."
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The editors of Radio Wales and Radio Cymru also appeared before the committee.
Radio Wales editor Colin Paterson said increasing his station's audience would help ensure more listeners in Wales accessed news about their communities, in the absence of Wales-focused news on Radio 1 and 2.
Mr Paterson said he was determined to increase the audience of Radio Wales and that he was focused on improving the experience for listeners after "audience challenges" had prompted a "renewed focus" on boosting the station's ratings.
Radio Cymru editor Betsan Powys said her station had "fairly healthy" listener figures at the moment.
"Not so long ago, even among fluent Welsh speakers - Radio Cymru's obvious target audience - their favourite station was often Radio 2.
"So I am pleased that Radio Cymru is once again the favourite choice of that group, not to mention the audience we are targeting who are a little less fluent or who listen to lots of other stations."
But Ms Powys told AMs that FM technology sometimes made it difficult to sustain the service for some of its core audience.