In the UK at least, you can buy active GSM repeaters or signal boosters but they are illegal to use - who said the law was stupid. Several of the mobile networks also have their own devices that they sell but they require power and connection to your personal broadband.
In the good old days I would have just plonked an external aerial on the house and plugged my phone into that, but many modem phones don't have external aerial ports these days. So, what's the answer?
A wave guide!!
A wave guide is a simple arrangement of two aerials connected with a piece of coax. The idea is that that one aerial; usually a beam so it's highly directional and gives a bit of signal gain, located outside, as high as possible and pointing directly at the transmitter, is connected via a piece of the shortest and highest quality coax you can get your paws on to a small suitable indoor aerial. Signals are picked up by the outside aerial, travel down the coax and are re-broadcast by the indoor aerial. The trick is you don't want the aerials to close together that they interfere with each other and since you are not adding any amplification (as it's illegal and would mess up the GSM signal anyway), you need to keep cable runs as short as possible.
I decided to re-locate my communications aerial to the back of the workshop so it was as close as possible to where I spend the majority of my time.
The aerial above shows an extension pole, a wide-band communications aerial on the top (white stick), a black GSM aerial mounted on the side that is connected directly to a piece of kit in the workshop, and the main GSM beam aerial; aligned for vertical polarization.
The communications and black GSM aerials are working great.
However, I need to wait for my friend to come over next week with his spectrum analyser so we can align the main beam aerial. The aerial, but it's very nature is highly directional and because of the distance to the cellular base station, being out of alignment by a fraction of a degree will seriously degrade the set-ups performance.
We will plug in the analyser and very slowly scan the aerial left and right till we see a peek on the analyser at the correct frequency for O2 then lock down all the bolts.
What could possibly go wrong.
Once it's all up and aligned I'll report back on it's performance.