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What Does "Signal Booster dB Gain" Number in Decibels Mean?

Jul 24, 2018

What Does

Let us examine what the positive number followed by dB means in specifications of any cell phone signal booster. Then we will examine what a negative number followed by dBm means when you measure cellular signal strength in your smartphone, or signal meter.

The bars on your cellphone don't say much.

When you look at the bars on a cell phone that indicate the signal strength, it is an easy way to get an indication of how good the cellphone signal is where you are. If you're struggling to make a call, you could even use it to find a place where the signal is better. The number of bars on your phone does however vary substantially depending on which carrier and smartphone you use.

While one carrier might only show 1 bar, another may show 3 bars, even though exactly the same signal strength is received and both signals have exactly the same speed. The reason for this is unfortunately because there's no standard that specifies how carriers and cell phone manufacturers must symbolize signal bars.

All cell phones do however have a way to display decibel (db) gain that is more technical and accurate. Decibels (dBs) is a unit of cellular signal strength measurement.

Gain is measured in Decibels and this is what those positive & negative numbers mean.

What exactly does a "cell phone signal booster dB Gain" value mean? Gain is stated as a positive number on cell phone signal booster kits. It denotes the increase in signal strength. For example, the lowest Gain boosters, our in-vehicle phone cradle signal boosters offer up to +23 dB Gain. Although we mention "lowest Gain" here, an increase in signal strength of even +23 dB is very significant. Please see the graph at the top to see how much even a +23 dB Gain increase boosts the signal strength. Our higher Gain in-vehicle wireless multi-device boosters offer up to +50 dB. The highest Gain cell phone signal boosters are home wireless multi-device boosters which offer signal Gain of up to +72 dB.

Decibel Milliwatts (dBm) detector software built inside all smart phones is used to measure signal strength being detected by that phone on that phone service carrier's network. It is a negative number. For example, here're three scenarios that will explain this better:

  • -50 dBm normally means that you have a very good signal (best signal for all practical purposes), and will show as full bars on your phone.
  • -80 dBm to -90 dBm is medium signal strength and would enable phone conversations, albeit user may experience occasional dropped call and minor static in conversations.
  • -110 dBm would mean that user will not have any signal reaching the phone, and is in a dead zone. In this zone, it may display "no service" and may show no signal bars. Attempt to make outgoing calls would result in redial suggestion, and incoming calls will go directly to voicemail.

Now you can see how positive number dB additions of up to +23dB, +50dB, or +72dB to those negative dBm numbers of -50dBm, -90dBm, -110dBm makes such a huge positive impact to those negative signal strength dBm figures. dBm denotes an absolute power level measured in decibels. It is referenced to 1 milliwatt (mW). To convert from absolute power "P" (in watts) to dBm, use the formula dBm = 10*log (P/1 mW). This equation looks almost the same as that for Decibel (dB). However, now the power level "P" has been referenced to 1 mW.

Understanding Signal Strength & Gain Values In Context of Using Your Phone.

Understanding Gain in Decibel (dB) & signal strength in Decibel Milliwatts (dBm) helps us understand how everything related to wireless signals work. This includes cell phones, cellular networks, and signal boosters. The signal increase versus dB Gain graph figures shown at the top apply universally to all cellphones and their service providers. When you experience very slow internet, lost connections, or dropped calls, it probably means you're close to the dead zone. The reason for this may be the distance from cell towers or obstructions along the way. See diagram below that illustrates this for you in context of dBm values.

Cellular Signal Strength in Decibel Milliwatts dBm Scale Excellent to Poor

Cell phone signal boosters are becoming increasingly popular as cellular devices. Just like smartphones, cellular amplifier kits are being used more often and in more variety of places such as homes, buildings, retail stores, and vehicles. Cell phone signal boosters amplify the dB level to be close to -50 dB. This results in better connection and signal on both 3G and 4G LTE. Signal Gain a signal booster kit offers is an increase of that current signal strength your mobile device experiences.

Using a Smart Phone to see the real Signal Strength in Decibels (dBs).

While professional tools such as a signal meter provides realtime accurate figures of signal strength from all carriers, a Smartphone can be used to get the job done. A couple drawbacks are that: 1) The smart phone will only detect signals of the specific service provider whose SIM card exists in the phone. 2) It may need up to 1 minute to update the signal strength number at each spot you wish to measure it. Now that you're aware of these two minor limitations, please follow the easy steps below to see the real signal strength in dB on your phone:

For an Android phone:

  1. Go to Settings.
  2. Tap on General.
  3. Select About Phone.
  4. Go to Status or Network.
  5. Your dB Value should be displayed.

For an iPhone:

  1. Switch to Phone Mode.
  2. Dial *3001#12345#* and make the call.
  3. The phone will switch to Field Test Mode.
  4. When you now drag down the notifications bar, the dB reading will be shown in the left-hand corner.

Why you need to understand dB Gain?

When deciding to buy a cell phone signal booster, one of the things you need to evaluate is the gain of the specific model.

dB gain is used to measure the amplification power of a signal booster. This means that a +11 dB gain is better than a +8 dB gain. dB gain is however not linear, but exponential. This means that there is a huge difference between gains of +8 and +11.

A +11 dB gain will in fact give you double the power of a +8 dB gain!

If the gain does up by +3 dB, the signal strength doubles. If the gain goes up by +10 dB, the signal strength improves by 10x, while a +20 dB gain translates to 100x more signal strength.

To give you some idea of the numbers, our in-vehicle phone cradle signal boosters offer up to +23 dB Gain, in-vehicle wireless multi-device boosters offer up to +50 dB, while in-home wireless multi-device boosters offer up to +72 dB.

Although it is logical that +72dB is better than +50dB, the power increase is however much more than what you might think.

As mentioned before, +3 dB gain doubles the power of the signal, while 10x the power is achieved with a +10 dB gain, and 100x the power with a +20 dB gain.

This means that in-building wireless multi-device boosters are 100 times stronger than in-vehicle wireless multi-device boosters are. This makes sense, as building signal boosters need much more power to cover a bigger area. There are however other factors that need to be considered, including interference from building material, and distance from the tower. The signal strength is therefore not a guarantee, but it will give you a good indication of what you might receive.

When you compare cell phone signal boosters, take note of the gain in dBs - it makes a big difference. The difference from +60 to +65 dB might not seem like much, but it delivers 3 times the signal amplification.

The table below shows the dB gain and the power increase for different signal booster types.

dB Gain Signal Power Increase
23 dB Power increases 200 times
50 dB Power increases 100000 times
72 dB Power increases 16 million times

 

Important consideration before purchasing any cell signal booster.

Please note that despite such amazing exponential multiplications, if there's no signal at the best signal strength spot where you would install your exterior antenna - A signal booster will definitely not work. Zero multiplied by infinity (∞) is still zero. Therefore, there must be some signal available for cellular boosting system to boost, for it to help with poor reception. If not, please contact us for other options available such as Small Cell and Active Distributed Antenna Systems (Active DAS) that provide signal through direct underground feed from the respective carrier network(s). Such complex cell tower simulating signal enhancement systems require service carrier collaboration and are typically more expensive plus require professional installation by certified installers.


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4 comments

  • This might sound like a bunch of goobledy gook (that’s what it seemed like to me when I first read it), but decibels are an important indicator of what strength cell phone signal you’re receiving. Make no mistake about it, if you have a weak signal, you’re likely to experience dropped calls, slow data uploads and downloads, lousy reception, and a larger drain on your phone’s battery as it struggles to pull in a decent signal. Don’t waste your time reading your phone’s bars, look at the DB levels as they mention here.

    Ricky Greene on
  • Zero times infinity still means zero. That’s an essential when it comes to cell phone boosters. If you are somewhere where there is no cell signal at all, a booster won’t help. If you are somewhere with a weak signal, you are in business as a cell phone signal booster will amplify the signal. This was informative in explaining why signal bars aren’t reliable. Not sure why this isn’t common knowledge, but most people (myself included) just look at the bars when it comes to gauging their phone’s signal strength.

    Tom Palmerston on
  • Now I have a good idea how to tell what kind of signal I’m getting with my cell phone. It’s been ridiculous looking at the bars and seeing if I have a strong signal or a weak signal. I’ve had three or four bars with poor connections and super-slow downloads and then the opposite with one bar. Not sure where things are going with getting Wi-Fi and cellular boosters. I’m certain I’ll be getting an interior cell phone booster for my home, but I may hold off on the Wi-Fi one.

    Dean Hamilton on
  • Holy smokes. This article really helped me understand not only how cell phone signal boosters work, but how to read your phone and see how a booster does its job (increasing an existing signal so your cell phone or other mobile device has the signal strength to do its job effectively). I want a cell phone booster to increase my signal so I can hear the person on the other line clearly and avoid dropped calls. Your phone has its own cell phone signal strength meter but it isn’t the signal bars. As this article makes clear, signal bars are next to useless and the only way to check your phone’s signal is to dig deeper. That will help you understand whether or not you need a mobile phone signal booster because you can check it over time and see if you’re getting a weak or a strong signal on a regular basis.

    Perry Ostrander on

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