Listener Derek got in touch with this question - "I can sit at my work desk, with my phone by my side, and the signal strength display goes from saying "no service" to 4 bars out of 5, within a couple of minutes, for no obvious reason. It varies like this all day, every day. I can understand why some places have good coverage, and others have bad coverage, but why should it vary so much in one place?" We asked signal expert Ramsey Faragher from Focal Point Positioning and Cambridge University to dial up an answer to Derek's question about wandering mobile phone bars... Like this podcast? Please help us by supporting the Naked Scientists