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Why Do We Still Use Signal Bars?

by Travis Harvey | July 12, 2010July 12, 2010 10:10 am PST

In recent memory, nothing has stirred the reception pot like the iPhone 4.  It took less than a day to discover the death grip and the signal loss that came with it and little words came from Apple until they released a statement about their ‘shocking’ discovery that the formula used to display signal strength is “totally wrong.”  You know what’s totally wrong?  Relying on a five bar scale to determine how good reception is.

AT&T’s 3G signal ranges from -51 dB (strongest) to -113 dB (lowest functional).  As it stands, the iPhone would display five bars for any signal ranging from -51 dB to -91 dB.  That means that of the 62 dB range, the iPhone would display 5 bars for a drop in reception by 40 dBs.  Four bars range from -91 dB to -101 dB, three bars range from -101 dB to -103 dB, two bars from -103 to -107, and one bar from -107 to -113. (Reception according to AnandTech w/ handy bar graph.)


AnandTech put the iPhone 4 through its paces in different locations and discovered that the worst case scenario with the death grip is a drop of 24 dB in signal strength.  Depending on the signal strength you’re normally getting, this could result in a loss of all displayed bars.  They use the following example:

“However, in locales that have less signal, but where iOS still displays 5 bars, the drop of 24 dB is visualized much differently. For example, at another test location, signal without holding the phone is -89 dBm, which is still displayed as 5 bars. Cup the phone, and you’ll fall all the way to -113 dBm. All the bars dramatically disappear one after the other, people think they’ve dramatically lost all the signal, and you know the rest.”

Clearly there’s something wonky since a signal of -90 dB displays the same as one with -51 db.  Reception fluctuation in decibels isn’t linear so a drop from -51 dB to -61 dB isn’t as big of a hit to reception as a drop from -103 dB to -113 dB would be.  Of course it’s unlike that we’ll see dB readings replacing our beloved bars since most people would have no idea how to read them.  Wouldn’t it make more sense to display reception as a percentage of what’s possible?