I have a TV with an internal Freeview tuner. 

All channels pixelate  approx every 30 seconds then return to 100% picture. 

On checking the signal strength and signal quality for all muxes I find the Signal strength on each mux remains at 100% but quality varies from 100% then back to approx 25%. I installed a filter to see if Cellphone UHF signals were interfering with the quality but no improvement.

The UHF aerial is less than 5kms from the nearest transmitter in central Hamilton and the problem occurs on calm sunny days and in wild weather, so it's not a weather issue.

Could the problem be that the signal is too strong and will an attenuator fix the problem?