Cell Phone Booster Units – What They Are and What they Can and Can’t Do

Have you ever felt a sudden attack of panic because your phone shows no signal? Here’s a way to minimize such concerns.

The good news for most of us is that while driving around our local urban/suburban area, to and from home/work/shops, we seldom experience any issues with cell phone service or getting a good signal.  If we do, it is usually no more than a few seconds before our car moves into a better coverage area, and as likely as not, we don’t even notice the brief outage.

Even out of town, as long as you stick to the interstates, you’re probably fine with good signal coverage most places.

But when you go into rural areas, off the interstates, away from the towns, and especially into hilly territory, your cell phone signal becomes less guaranteed.  If you have a problem – stalled vehicle, flat tire, whatever – you may find yourself with the double problems of being unable to call for help and not having anyone else drive by.  And that is the bad news – we’ve become more dependent on our phones than we realize, a realization only truly appreciated when we can’t get signal.

And, in obscured reality, even the most developed of towns and cities often have small “black spot” areas – that is certainly true where I live, in a Seattle suburb and not far from Microsoft’s World Headquarters – an area you’d expect to be perfectly covered by all the service providers, but which astonishingly, is not.

Those of us longer in the tooth may remember the early cell phones that required external antennas on our vehicles.  Then there were cell phones that had antennas that would extend out of the cell phone body.  Now there is neither.

But this isn’t because phones have become “better” at sending and receiving signals.  The underlying physical laws of radio transmission and reception haven’t changed, although receivers are perhaps a bit more sensitive and selective these days due to digital filtering.  Instead, what has changed is that in much of the country, there is better coverage, with more cell sites closer together, meaning our phones can make do with less efficient transmit/receive functions, because they don’t need to communicate so far to reach a nearby cell tower.  But as soon as you get away from the high density of cell sites in populated areas, a modern phone will struggle to connect to the increasingly distant towers and soon will lose all connectivity.

In weak signal areas, you’ll also notice your data speeds slowing down, and for many of us, these days the quality of our data connection is more important than the quality of our voice connection.  People don’t realize that the reason data might be slow is not due to their phone or network congestion – as often as not, it might be due to a poor/weak signal between their phone and the cell tower it is communicating with.

Back in the “good old days” – before Apple changed cell phone design priorities from functionality being most important, and instead made appearance the major criteria – there were usually ways you could plug an external antenna into your phone.  A simple change from relying on a tiny antenna on the phone in your pocket to using a scientifically designed antenna on the roof of your car could double the phone’s range.  That’s no longer possible, the same as changing a battery is also no longer possible, because it is “prettier” not to have a removable case and not to have an external antenna connector.

Fortunately, all is not lost.  If you travel in weak signal areas, there are devices known as “boosters” that you can add to your vehicle to “magnify” the cellular signal, giving you better connections over longer range.

This article explains what they are and how they work.  It also helps you to understand if one might be useful for you, and just how much extra range you might get from one.

A note to people who know a lot about radio theory – yes, I know I’m using the wrong terms loosely in this article.  That isn’t because I’m ignorant.  I’m a highest level Amateur Extra licensed operator and VE myself (NZ9G).  I am deliberately misstating and simplifying the complexities of radio propagation and antenna theory for the purpose of clarity of concept, not due to ignorance at my end.

This article is intended as an introduction to our companion article which reviews the latest and greatest Wilson weBoost Drive Reach Cellphone Signal Booster.  The concepts in this article of course apply to all signal boosters, not just to the Wilson products.

Cellular Signal Boosters

A cellular signal booster makes weak signals stronger.  It can’t however take a signal that is too weak or totally non-existent and make it into a good signal.

A booster makes weak signals stronger in three ways.  The first is that it has a better quality and larger antenna than your cell phone has.  This makes it better able to “hear” very weak signals, and equally means that your phone’s own transmissions are sent out more “strongly” so they can in turn be heard further away by cell towers.

The antenna in your cell phone has an “efficiency” rating of probably somewhere between -2 and -10 dBi.  The Wilson antenna with the unit we review has a rating of  between +1.1 and +2.0 dBi (the rating varies depending on the frequency band; higher frequency bands have better ratings with this antenna).

We’ll not explain what we mean by “efficiency rating”, and indeed will even try to avoid explaining the term dBi (Google it if you are interested).  The two points to appreciate are that higher numbers are better than lower numbers, and each difference of 3 dB (or dBi or dBd) represents a doubling in receiving/transmitting ability.

So, all other things being equal, a typical mobile signal booster’s better antenna gives you at least an immediate doubling of receiving/transmitting ability.

The second way that the booster gets a better signal to your phone is by taking its better antenna out of the vehicle and placing it on the roof.  This further boosts the efficiency and effectiveness of the antenna.

Much of the cell phone wireless signal works on a more-or-less “line of sight” type of concept.  If your antenna can see the cell tower’s antenna (minor obstructions are okay, major ones are not), there’s a good chance the two units will be able to talk to each other.  But if there are buildings and other structures blocking the direct visual sight of each antenna to/from the other, then their ability to talk to each other will massively reduce.

Simply taking the antenna out of inside a vehicle (which has lots of metal shielding, blocking many radio signals from passing through) and taking it outside the vehicle is a tangible improvement.  Mounting it higher up – even just a few feet higher on the vehicle roof – gives it even better line of sight and to further away places.

These first two enhancements are admittedly low-tech.  But they’re also very important.  Because the third way a signal booster makes weak signals stronger is that it takes what it “hears” through its outside antenna, amplifies it, and then transmits it through its inside antenna.  The better the signal it hears (ie receives) the better the quality of signal it retransmits.

Think of this like the amplifier on a PA system.  Turn the volume up (ie use a booster) and whatever the PA system’s microphone (outside antenna) hears gets blasted out the speakers (inside antenna).  If the person speaking into the PA is a long way from the microphone (ie a weak signal poorly received) then the PA system will broadcast so much background noise that what the person is saying will be heard loudly but not clearly (because all the background noise has been amplified too).  Have the microphone move closer to the person speaking (ie get a better antenna) so that it hears the person better (receives a better signal) and the quality broadcast through the speakers (internal antenna and to your phone) doesn’t just get louder, the speech gets clearer too with fewer distracting background noises also being picked up and amplified.

That is why a booster unit will only help if it can receive some signal in the first place.  Just like a PA system won’t help if the person’s voice it is amplifying is on the far side of a busy road from the microphone, no signal booster will help if there’s no discernable signal to start with.  With the PA system, you just get traffic noise, with the booster, you just get random electronic noise.

What the Cellular Service Provider Coverage Maps Don’t Tell You

So, noting that the booster needs to have some sort of a weak signal to start with, does that mean that if your phone can’t get a signal, will a booster be of any help?  Does it mean that if your carrier’s coverage map shows no signal at a location, a booster will be useless?

Yes and no.  For sure, if the booster was connected to the antenna in your phone, it would not provide any real value at all.  But, that brings us back to the point we looked at before – the better quality more efficient external antenna that provides the input to the booster.  It can still “hear” a faint signal long after your cell phone antenna has failed to pick it up.

And that’s the hidden “bonus” that isn’t revealed on a typical carrier’s coverage map.  It shows you the typical area that a typical cell phone with its typical internal antenna will pick up usable signal.  It doesn’t show you the extended area which a unit with a better antenna mounted on a vehicle roof would still keep picking up usable signal.

Note also there is no formal standard (that we’re aware of) that the wireless companies much use to define when coverage goes from satisfactory to unsatisfactory, and sometimes the maps might be a bit optimistic (or even a bit pessimistic).

How Much Extra Range Will a Cell Phone Booster Give You?

For most of us, this is one of the key questions we want (need!) to know the answer to.  How much extra range will you get by using a good booster?  The short answer to that is “it depends”.  There’s not an exact scientific answer.

The longer answer is that it depends on how/why the range of the cell tower is limited.  There are likely to be one of two reasons that might apply.  Other reasons also exist but are less common in low density coverage areas.

The first limiting reason is that the signal gets blocked.  For example, you go down into a valley and lose the all-important “line of sight” link to the cell tower.  If this is the reason why the usable signal ends where it does, then any booster/every booster is not going to make much difference at all.  The signal is being blocked by the obstacle, and you can’t boost no signal.  The booster might give you an extra 100 yards of coverage, maybe, while the signal drops down to almost zero, but that is all.

The second reason is that while the cell tower remains in direct (theoretical) line of sight, the signal gets progressively weaker the further away you travel, and it reaches the point where it is too weak to support a connection.  In this case, the booster will make a big difference.

So, what does it mean to make a “big difference”.  It might possibly double the distance that you can get a usable signal from the tower, maybe even more.  But that distance varies, especially depending on the tower’s frequency and beam shape and transmitting power.  Maybe the tower had a one mile range and so you get one or possibly two more bonus miles of range.  More likely, the tower has a 5 – 10 mile range and so you get perhaps another 10 miles of range on top of that.

There is an interesting maximum range, set by the GSM specification to 35 km (22 miles) at which a phone can communicate with a tower, no matter how clear the signal.  This theoretical maximum is due to the need for precise timing and synchronizing of the signals between the phone and tower.  Even at 186,282 miles per second (the speed of light and radio waves), the unavoidable propagation delay that increases with distance becomes a problem (which gives you a sense for how these things are timed down to fractions of a milli-second).

Not all but most cellular service is subject to this specification, although we’re told by Wilson Electronics that they’ve seen up to 30 miles of range achieved by a phone using one of their boosters, so there are cases where your range can extend quite extraordinarily.

So, to answer the question, and with some exceptions, the extra distance from a cell tower you’ll get with a signal booster can vary from almost nothing up to perhaps about ten miles in normal use.  In real world terms, it might mean the difference between going through dead spots and losing coverage without a booster, or staying online and connected even at the fringes of each tower’s coverage area.

Measuring Signal Strength

So, do you need a booster or not?

You’ll sort of know the answer to that question anyway – are you aware of losing signal and connection at times, or is everything working well and reliably?  More subtle is a question about if your internet speeds are consistently fast or sometimes very slow.

Many people think they can judge their signal quality by the number of bars of signal strength showing on their phone.  But these signal strength bars are more a marketing fiction than a reliable indicator of signal strength or quality.  There is no “standard” for determining what should register as five or four or any other number of bars.

Each manufacturer sets their own levels; indeed, some years ago Apple responded to complaints about poor signal receiving on one of their iPhones by simply changing the levels and the bars they corresponded to.  If a person sees four or five bars of signal, they are more likely to be happy (or at least accepting) of their call quality than if they see one or two bars, so many manufacturers show lots of bars, even for very weak signals.

The good news is that if you have an Android phone, there are a number of free apps that you can add to your phone that will provide you with a lot of technical information about the signal quality you are receiving.  The best of these is probably Network Cell Info Lite, or to give it the full name of the app, Network Cell Signal & WiFi Info Lite, by M2Catalyst, LLC.

Sadly, if you have an iPhone, you are stuck within Apple’s rigid system that doesn’t even allow apps to access or report extensively on the phone itself.  Here’s a way you can cajole your phone to at least share some data with you.

The key measurement is your signal strength in dBm – sometimes referred to as RSRP.  The lower this number, the better.  It is unlikely the number will ever be larger than -40, and unlikely you’ll see it drop much below -120.  Numbers greater than -100 (ie going from -100 to – 40) range from acceptable signal to great signal; when you start going below -100, you’ll be more liable to start experiencing problems.

Another interesting number to observe is the RSRQ number.  This is the Reference Signal Received Quality number, where again, the larger the number, the better.  Usually you’ll see numbers in the range from about -3 to -15 dB or so.

If you want to go wild and crazy, you can also look at the SNR or Sinr or CINR or RSSNR reading – the signal to noise ratio.  Again, the larger the number, the better, but this time, you’ll see positive rather than negative numbers.  Look for values over 8 dB, and ideally over 16 dB.

A booster will most improve your signal strength.  It will indirectly improve your RSRQ, and can’t do much for your SNR.

The Three Benefits of a Cellular Signal Booster

Most people can think of one benefit of a booster – better range, but seldom consider two other possible benefits.  In theory, there are three things you’d expect from a signal booster.  In reality, only two of them are likely to apply.

Better/Longer Range

This is the obvious benefit of a booster, and is discussed above.

Better/Faster Data

When signal quality drops, so too does the data bandwidth.  Our testing with the Wilson booster showed dramatic increases in data speeds.

There’s no easy way to say how much your data speeds might improve.  It depends on the speed you’re getting at present – if you’re already at close to the maximum speed that either your phone or the tower can support, you’ll not get much more speed with a booster.  But if you’re in a marginal area with speeds that have dropped way down, you might get as much as a ten-fold increase in speeds.

The speed increase also depends on how much data bandwidth the tower could make available to you if you had a better connection.  Our sense is that most of the cellular towers could never service all the phones connected to them if they all simultaneously requested fastest speed data, so the maximum speed varies depending on how many other phones are using the data at the time you wish to use it to.

Better Voice Quality

This is the interesting benefit that you’re unlikely to experience.

If you had an analog type connection between your phone and the cell tower, like an AM radio, then better signal would definitely mean better voice quality.  But with a digital connection, the sound quality tends to stay surprisingly confident as the signal gets weaker, then, all of a sudden, it just stops entirely.  The “magic” of a booster isn’t so much in making poor quality connections better, but rather in stopping your phone from dropping signal entirely.


Signal boosters can’t work miracles, although at times, it might seem like they are.  They can help improve weak signals, potentially increasing the coverage area when you’re in areas of marginal signal coverage, and their improved quality signals often translate to dramatically faster data speeds.

If you’re unaware of any limitations or challenges with your phone, then there’s no point in getting one.  But if your phone is often dropping calls, and if your data speeds are terribly slow, you should first use a signal measurement app to see if you have good or poor signal strength.  If the signal strength is good, then it is unlikely a booster will help.  If it is poor, a booster might dramatically improve your connection.

Several different companies manufacture cell phone signal boosters.  Wilson Electronics is a well respected American company and we have tested one of their weBoost units, reviewed here.  We can’t speak for other brands, but you do have choices, including SolidRF and SureCall.  If/when choosing a signal boosting unit, make sure it supports the wireless network and frequency bands that your phone supports.

2 thoughts on “Cell Phone Booster Units – What They Are and What they Can and Can’t Do”

  1. What about indoor signal boost antennas? Are they worthwhile; which is best. I think a more widespread problem.

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