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Cell Signal Strength

What do bars mean?

Bars on a cell phone usually are not an accurate measure of cell phone strength.  They are like a gas gage, they give you an idea of what the signal is, not the actual strength.  You can have two different brands of cell phones next to each other using the same carrier and they might show different bars.  Some carriers have bragged they have more bars than anyone else.  Once the carrier knows you have enough signal to make a call and talk, bars can be displayed anyway they want and the caller does not know the difference.
 
The image to the right shows a Motorola Droidx in a metropolitan area with 3 out of 4 bars.  I took this photo while I was writing this web page.
 

 

What is the real cell signal strength?

Many cell phones, especially the newer smart phones, have the ability to display the cell signal dB reading.  This is a much more accurate number than the bars.  On most Android phones this signal reading can be found by pressing the menu button on the front of the cell phone, then selecting "Setting", scroll down the screen and select "About Phone", then select "Status", towards the bottom of the screen you can see the "Signal strength" display like in the image shown to the right.  You will notice a number with a negative sign in front of it.  This dBm number may periodically change while you view it.
 

 

What does the dB number mean?

The dB number is a measurement in relation to a milliwatt.  Usually these kind of numbers are measured with RF meters that cost thousands of dollars so the accuracy might be off a bit with a $200 cell phone, but it should be close enough.
 
The closer you are to your carrier's cell tower the closer to -40 this number gets.  The farther away from your carriers cell tower you get, the closer to -100 you get.
 

dB Signal - A basic guide

  • -50 to -60 (very strong, near a cell tower)
  • -60 to -70 (extremely good, rare)
  • -80 to -85 (normal downtown)
  • -90 to -95 (getting on the weak side)
  • -95 to -98 (weak, dropping calls)
  • -98 to -100 (bad, hard to stay connected)
  • -100+ (basically no usable signal)
 

Why does cell signal fluctuate?

Signals from cell towers fluctuate up and down around 5dB.  This fluctuation is caused by several diffeent things.  One of the main reasons for cell signal fluctuation is the load on the tower.  The more people using the tower, the weaker the signal.  You might notice the strength of your cell signal in a certain area change depending upon the time of day because of rush hour or lunch hour, etc.
 
Not only the number of callers, but smartphones and their ability to view and stream data can put considerable load on a tower.  These types of activities cause a cell tower cell signal strength to constantly change.  If your cell signal is -95 you can usually talk all day.  If your -95 signal fluctuates down to -100 because of the load on the tower, you might drop the call for a moment, but be able to redial and resume in a couple of seconds.
 
 

Concrete, Metal, Low-E Glass and Shadowed areas

You can be near a cell tower, but still have a weak cell signal.  Many building materials such as concrete, metal, and low-e glass reduce or block cell signal from entering into a building.  Stucco with its wire mesh, metal roofs, large logs, and vapor barriers in attics also impead cell signals and cause weak cellular reception inside buildings
 
When your outside, dense forest, bluffs, and hills do a good job of reducing or blocking cell signals.  Even low areas around lakes, rivers can have problems.  A lot of times in low areas, there is a signal, but it is above you.
 
Cities with there tall buildings have different types of problems.  Sometimes the top floors of buildings, 40-50 stories up can not get a good cell signal because towers are broadcasting at a lower elevation.
 
 

I can see my tower, but I have no signal.

Sometimes you can see your carriers tower down the road or off in the distance, but you still have a bad cell signal.  Just because you can see the tower does not mean that the tower is broadcasting in your direction.  This type of issue is more common along remote freeways where cell signal broadcast is concentrated up and down the freeway and not too much to the side.  Directional sector antennas are used on cell towers to direct the broadcast of signal in certain directions.  Just because you can see the tower does not mean that it sees you.  Also, are you realy sure that it is your carrier's tower.
 
 

Frequency and technology limitations

Different frequencies can carry different distances.  Carriers that use 800MHz frequency range can broadcast their signals more than twice the distance of Carriers that use 1900MHz frequencies.  So why don't all the carriers use 800MHz.  There are only so many licences available and when they are gone, other frequencies have to be used.  800MHz also has better penitration capabilities than 1900MHz, so cell signals in buidings may be stronger with 800MHz compared to 1900MHz.  If you can find out which frequency your carrier uses in your area, you might be able to answer some of your reception issues.
 
Another factor is the technology.  GSM vs. CDMA.  CDMA technology has the ability to broadcast farther distances than GSM.  Timing is a factor in this area.  The farther you are away from a tower seems to effect GSM more than CDMA.  Verizon, Sprint, US Cellular are CDMA carriers.  AT&T and T-Mobile are GSM carriers.
 
 

Summary

We hope that this information helps you understand cell signal strength and hope other variables effect it.  Powerful Signal (www.PowerfulSignal.com) has a complete offering of cell signal booster systems and components to help solve your weak cell signal problem.