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The Surprising Truth Behind Cell Phone Bars and dBm

on 5th Aug 2019

dBm blog header

Ever wondered how to get the best measurement of your cell phone’s signal strength? Those coveted signal bars we’re constantly bending, twisting, and stretching to gain better access to?

They’re purely aesthetic. While they’re somewhat helpful to get a general idea of how strong your signal might be at any given location, it all depends on the algorithm your carrier or phone uses to represent decibels as cell phone bars.

While the friend sitting across the table from you might have three bars, there’s a good chance that your two bars are just as strong, if not stronger. It’s the carrier, as well as the make and model of your phones, that are out of sync — not your actual signal strength. This isn’t to say that those bars are useless - they’re just overly generalized and lack a universal starting point. In order to more accurately gauge signal strength — say, for the optimal placement of a cell phone signal booster — the key is less acrobatics and instead, a better understanding of decibels.

What is dBm?

The decibel (dB) is a relative scale used to represent the power and voltage strengths of electronic equipment, like signal boosters or the wires and cables that connect to radio and audio frequencies. Because the decibel is logarithmic and therefore a dimensionless unit, we apply the unit dBm, or decibel-milliwatts, as an absolute point of reference.

This means that power — in our case, signal strength — is measured in reference to one milliwatt, and can be calculated as ten times the log of the signal strength in milliwatts. The dB simply quantifies the ratio between two values, and those values are measured by dBm. So once the dBm has been established, only then can you measure any change in decibels (dB).

Its capability to express values both large and small in short form makes dBm the measurement of choice in radio, microwave, and fiber optic networks. In the world of cell phone signal boosters, dBm measurements represent the strength of a signal at any given location, as well as the amount of power an antenna is capable of amplifying.

dB, dBm, and Signal Strength

Typically, a strong outside signal would clock in somewhere around -50 to -70 dBm, while anything below -100 dBm would be considered weak (-110 means no signal at all). The use of an indoor antenna could boost that outside dBm signal exponentially — for example, an indoor antenna that is radiating -20 dBm can effectively cover about 3,000 square feet. According to the logarithm, the signal strength doubles with every third decibel, meaning that a dBm signal strength of something like -70 is actually twice the power of -73 dBm. The numbers may not make it look like a great change has occurred, but in reality, the decibels have grown exponentially.

How Do I Take dBm Measurements on my Phone?

When the strength of your cell phone signal matters most, skip the bars on your screen and opt for the master precision of dBm signal strength measurements. Whether it’s choosing the strength of your cell phone signal booster or figuring out where to install it for optimal efficiency, apps like Network Cell Info or inPocket Software make it easy to monitor and measure the dBm in real-time, everywhere you go. Android phones offer a decibel-reading function in their settings, while most iPhones can access decibel information by turning on “test mode”. Simply “call” the number *3001#12345#* from the keypad, and the dB reading will either appear in the top left corner, or can be found by sliding down from the top edge.

An accurate reading of your dBm signal strength will not only optimize the performance of your cell phone booster antennas and amplifiers, but you’ll also sound like a true tech wizard the next time your friends are flailing their phones around in search of those elusive bars.

Any questions? Feel free to leave a comment below:

How May We Help You?

Wilson Amplifiers is the leading provider of cell phone signal boosters. Cell phone boosters amplify 4G, LTE, and 3G signal for any phone with any carrier for home, office, or vehicle.

We seriously hate dropped calls and poor coverage, so it's our goal in life to stomp on spotty signal like the little roaches they are:

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