How Mobile Signal Boosters Work
We bring the outside signal inside the building!
Mobile signal boosters aren't magic.
In simple terms, they take usable mobile signal from outside a building and make it available inside, where walls, glass, steel, concrete or simply the size of the building have stopped it getting through properly.
The basic idea is actually pretty straightforward. Doing it properly is where things get interesting.
You need enough usable signal outside. You need the right frequencies. You need to know which mobile networks matter. You need sensible antenna positions. And you need a system designed around the building rather than a box somebody has bought because it has the biggest number printed on the front.
So, here's how it actually works.
Booster or Repeater – What's the Difference?
Not much, in most conversations.
Mobile signal booster is the phrase most people use. Mobile repeater is the more technical term.
We're generally talking about the same basic thing: equipment that receives mobile radio signals, repeats them and provides usable coverage somewhere the original signal wasn't reaching very well.
Ofcom itself generally uses the word repeater, while recognising that people often call them signal boosters. www.ofcom.org.uk
So if we talk about a mobile signal booster on this website, don't assume we're talking about a different piece of technology. We're talking about repeaters.
The more important question is what sort of repeater?
What Is Actually in a Mobile Signal Booster System?
A proper commercial system normally has a few basic parts.
An antenna outside
Usually called the donor antenna. This is positioned somewhere with usable mobile signal – often on a roof or another suitable external location. It is effectively the system's connection back to the public mobile network.
The repeater
This is the clever bit in the middle. It takes the signal received by the donor antenna and repeats the appropriate frequencies. Exactly how it does that depends on the type of system.
Something to distribute the signal
We then need to get that coverage to wherever it's required inside the building. Depending on the building and technology, that might involve coaxial cable, structured cabling, fibre or a mixture of technologies.
Antennas inside the building
These are often called server or coverage antennas. They provide the improved mobile coverage where people actually need it. A small building might only need a limited number. A large warehouse, office building or multi-storey property can be a completely different proposition.
That's the basic principle:
outside network → donor antenna → repeater → distribution → indoor antennas → your phone.
Narrowband and Wideband Repeaters
This is where things start getting slightly more interesting.
You'll hear people in our industry talk about wideband and narrowband repeaters.
They're useful descriptions, although they shouldn't be confused with Ofcom's regulatory categories. The easiest way to think about it is this.
Wideband
A wideband repeater works across a relatively large chunk of a mobile frequency band. In crude terms, it hears a broad bit of spectrum and repeats it.
That can be useful, particularly if you want to support several mobile networks. But there is a downside.
It doesn't necessarily distinguish between the signal you actually want and all the other signals sitting around it.
Imagine you've got a very strong network outside the building and another network that's considerably weaker.
Simply amplifying everything doesn't automatically fix that problem.
More signal isn't always the same thing as better signal.
So What Is a Narrowband Repeater?
A narrowband – or more frequency-selective – system can be much more targeted. Rather than saying: “Give me everything you can hear.” we can effectively say: “These are the frequencies we're interested in.”
That gives us considerably more control.
It can be useful where one mobile network is much weaker than another, where a business primarily uses a particular network, or where the radio environment outside the building is complicated.
Does that mean narrowband is always better? No.
And this is where some of the marketing around mobile boosters gets a little silly. Wideband isn't automatically bad. Narrowband isn't automatically good. It depends on the job.
The important thing is knowing what is outside the building before deciding what should go inside it.
Single-Network or Multi-Network?
This is another thing that sometimes gets muddled up with narrowband and wideband. They're not quite the same thing.
A business might only need one network improved.
For example, if you've issued hundreds of corporate mobiles on the same network and that's the network that doesn't work inside your building, then solving that particular problem may be all you need. Other buildings are completely different.
- A hotel has guests.
- A car dealership has customers.
- A care home has residents and visitors.
- A warehouse has drivers and contractors.
- An office has employees, visitors and suppliers.
Those people are unlikely to be using one convenient mobile network between them. In that situation, improving several networks can make much more sense. There isn't a prize for boosting the greatest possible number of networks.
We design around who actually needs coverage.
What Are We Actually Boosting?
This is where the little signal-bars graphic on your phone becomes fairly useless. A mobile network doesn't consist of one single signal. Operators use different frequencies, different bands and different technologies, and those signals don't necessarily behave the same way when they meet a building.
You can have five bars outside and virtually nothing inside.
You can have one network working beautifully while another barely works at all.
You can have a perfectly strong-looking signal that still provides a pretty miserable service.
So when we carry out a mobile signal survey, we're interested in considerably more than the number of bars on somebody's iPhone.
Bars aren't engineering.
We want to understand what signal is actually available, which network it belongs to, how good it is and what happens to it as we move through the building.
Bigger Isn't Necessarily Better
This is probably worth saying plainly.
The most powerful mobile signal booster isn't necessarily the best mobile signal booster.
We're dealing with radio equipment operating alongside live public mobile networks. You can't just keep winding the gain up until everybody's phone shows five bars.
- The external and internal antennas need to be positioned properly.
- The system needs sufficient separation between them.
- The repeater needs to behave properly.
And the finished design needs to improve coverage without creating another problem somewhere else.
Modern compliant repeaters include technical controls intended to manage things such as excessive gain, unwanted emissions and oscillation. Ofcom's licence-exemption regime includes technical conditions designed to prevent harmful interference to mobile networks.
In other words: This isn't hi-fi. Turning the amplifier up to 11 isn't the objective.
Are Mobile Signal Boosters Legal in the UK?
Yes – provided you use the right equipment.
And this is probably the only part of this page where we need to talk much about Ofcom.
Ofcom allows certain mobile repeaters to be used without an individual licence provided they meet its technical requirements. Its current framework allows qualifying repeaters capable of supporting one or more mobile operators. Equipment that doesn't meet the relevant requirements can still be unlawful to use.
There is another distinction worth knowing.
Ofcom doesn't approve individual signal boosters.
It sets the rules and technical requirements. So when you see somebody advertising an “Ofcom approved booster”, we'd treat that wording with a degree of caution. Ofcom explicitly says it does not endorse or approve individual products.
We therefore talk about equipment being Ofcom-compliant or meeting the relevant licence-exemption requirements.
That's a more accurate description.
And that's probably as much Ofcom as anybody needs on this page.
So Which Mobile Signal Booster Do I Need?
This is usually the point where people expect us to recommend a model.
We won't.
Not yet.
Because before we can sensibly choose the equipment, we need to understand:
- which mobile networks matter;
- what signal exists outside;
- which frequencies are available;
- where the signal disappears;
- how the building is constructed;
- how much of the building needs coverage;
- where antennas can go;
- where equipment can be installed;
- and what you're actually trying to achieve.
Only then does choosing the booster make sense. Which brings us back to something we've said elsewhere on this site: You don't need to know which mobile signal booster you need. That's our job.
We'd much rather survey the building first and design something that works than sell you a box and hope for the best.
Survey → Diagnose → Design → Install → Commission → Test → Validate
