A company which wants to put up transmitters on Gower for a controversial police communications system is appealing against the refusal of planning permission.
The communications system will be used by emergency services
A public inquiry is taking place in Swansea to review the city council's decision not to allow Airwave to place the transmitters at Pennard, Oxwich and Cheriton.
Airwave says the Tetra system is safe, but local people are worried about the effects the radio masts may have on their health.
The company says the transmitters are needed to form part of a network to support the new digital communications system for the emergency services in the UK.
Councillors who refused the applications argued that the transmitters would detract from the scenery in Gower, which was designated an area of outstanding natural beauty in 1956.
One of the first to give evidence was Swansea council's development control committee chairman Gethin Evans.
He said: "With the masts to be placed in such places as they are now applying for then obviously it intrudes into an area of outstanding natural beauty.
"As councillors we have to protect that."
Some people have expressed health concerns about the Tetra system, which they say uses a frequency similar to electrical signals in the brain.
Margaret Jones told the inquiry: "They are saying that as long as we are within the prescribed guidelines they are OK.
"In 10 or 15 years' time we may find that they were wrong."
Airwave MMO2, which is behind the technology, says it operates within strict guidelines.
The Government and bodies set up to monitor emissions also say it is safe.
Airwave spokesman Peter Stitch said: "Safety is a matter for the Government.
"They have commissioned the National Radiological Protection Board and the Stewart Committee and very recently another report which says there is no demonstrable risk from mobile phones.
"There is no difference between TETRA, which is a system for police and emergency services, and ordinary mobile phones."