More than 300 pupils and parents from most of Haverfordwest's schools have marched on the town's police station in protest at a communication mast there.
Schoolchildren of all ages took part in the protest
Campaigners say they have health fears over emissions from the Tetra mast which will improve radio links for the emergency services.
Protesters said the mast was too near schools, nurseries and a home for OAPs.
The company behind the mast said it was safe and it would replace two more powerful analogue transmitters there.
O2 Airwave said it had no plans to move it but Dyfed-Powys Police said the station was a temporary location for the mast.
The Tetra system is being rolled across Wales and England to provide police forces and other agencies with more reliable and secure communications.
Parents claimed the police station was too close to eight primary and secondary schools in Haverfordwest and a more sensitive site should have chosen.
02 Airwave said in light of concerns it had applied for planning permission to place it at the town's Hawthorne Rise telephone exchange but was refused in the face of strong opposition.
On Friday parents and pupils of all ages converged on the police station at the end of the school day chanting "Stop tetra, stop it now". Many waved banners and placards while some wore silver foil hats.
Kirsty Watson, whose daughter Tess attends Mount Airey school said: "We can't understand why it's near to all the schools in the area.
"We are not prepared for our children to be experimented on.
"We know we can't stop tetra coming to the county but we can stop it being near the schools."
Shelly Hawkridge, whose son Josh attends Glancleddau school, said: "We're here today to get the mast moved.
"There are plenty of schools, nurseries, crèches and old people's homes in the area and they could not have picked a worse place to put it.
Children chanted 'No Tetra - Stop it now'
"We understand there are other sites where it could have gone." A spokesman for 02 said there was no evidence to suggest the masts were not safe and they had been placed on over 100 police stations in the UK to date.
He said emissions from the Tetra system were 1,000 times lower than internationally-recognised limits.
Inspector Dick Pope of Dyfed-Powys Police said the police station was a temporary site and subject to planning permission it would be moved elsewhere.
"I can understand the public concern but I can say categorically that we have required the company to confirm that the mast on Haverfordwest police station is a temporary mast and the force has a letter to that effect."