In reply to aln:
> reception is generally poor, which is ridiculous as I live near the top of a tower block which is festooned with mobile masts.
That is about the worst location possible for urban mobile reception.
The antennas are very directional, and they provide almost no signal directly below them. If they did fire straight down, they would be subjecting you to unacceptable radiation levels. The signal is also unable to penetrate through the fairly thick concrete roofs of many tower blocks.
You will almost certainly be connecting to a different antenna, which is likely to be some distance away, which is why your reception is poor.