Had occasion to whizz up and down the M5 a few times of late, and noticed that for about a mile around the Droitwich transmitter, my car radio drops out and I get static ... just curious as to what's happening ... presumably the overall RF landscape is so flooded with the output, the car radio just can't discriminate and pick up the tiny R4 signal ?
Never had a chance to take/make a call while it's happening, so I can't say if it affects cellphones.