Signal bars on a cell phone are usually not an accurate measurement of cell phone signal strength. Bars are like a gas gauge: They tell you the general range but not the actual amount of signal you're receiving. Two different brands of cell phones, using the same carrier, placed next to each other, might show different numbers of bars.
Some carriers brag that they have "more bars" in more locations than their competitors. When your carrier knows you have enough signal to make a call and talk, bars can be displayed any way they want and you won't know the difference.
Take a look at the notification bar at the top my Samsung Note 5 screen: The signal indicator says I have 4 bars (circled in red). To most people that says "very good signal." But is it, actually?
The signal your phone receives from a cell tower is measured in decibel-milliwatts (dBm), a unit of electrical power in decibels (dB), referenced to 1 milliwatt (mW). There are three things you need to know to understand how decibel-milliwatts work:
So, what is considered strong or weak cell signal?
Most smartphones can display the cell signal dBm reading. Using this number is much more accurate than looking at "bars."
(Notice how the phone above is receiving −95 dBm of signal, which is "fair," even though the number of bars at the top—circled in blue—is supposedly showing full strength!)
To see the signal strength reading on an iPhone, follow these steps:
This will put your iPhone into Field Test Mode :
The bars or dots at the left side of Status bar at the top of the screen will be replaced by a number showing the iPhone's received signal strength in dBm:
This change is permanent until you reverse it. To return your display to bars or dots, repeat step 1 (above); once you're in Field Test Mode, tap Back to Phone at the top of the screen, and your phone will be back in its original display state.
The signal strength you receive from a cell tower will increase and decrease, even if you aren't moving. At rest, you'll frequently see fluctuations around ±5 dBm. The fluctuation is primarily caused by two factors:
Because of shifting usage loads, signal strength from a cell tower to your phone is constantly changing. If your cell signal is −95 dBm, you can usually make a call without any problems. If your −95 dBm signal fluctuates down to −100 dBm because of the load on the tower, you might drop the call for a moment, but be able to redial and resume in a few seconds.
You can be close to a cell tower, but still have a weak cell signal. Many building materials—including concrete, metal, low-e glass, wood, and plaster—will reduce or block cell signal from entering into a building and reaching your phone. Stucco with wire mesh, metal roofs, large logs, and vapor barriers in attics also impede cell signals, resulting in weak cellular reception.
Even if you're outdoors, dense forest, bluffs, and hills will reduce or block cell signals. Low areas around lakes, rivers, and gullies can have problems—there is a signal, but passing way over your head.
Dense urban areas with tall buildings have a different set of problems: Sometimes the top floors of buildings, 40–50 stories up, can't get a good cell signal because towers are broadcasting at a lower elevation.
Sometimes you can see your carrier's tower down the road or off in the distance, but you still have weak 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 highways where cell signal broadcast is mostly concentrated toward the highway and hardly at all behind the tower.
Directional sector antennas used on cell towers broadcast the broadcast of signal only in certain directions. Just because you can see the tower does not mean that it sees you.
It's also possible that the tower nearest you is operating for a different carrier than the one you're using.
Different frequencies carry different distances. Carriers that use the 800 MHz frequency range can broadcast their signals more than twice the distance of carriers that use 1900 MHz frequencies. There are only so many FCC licenses available for each band of frequencies, and when they are all claimed, carriers have to use other frequencies. 800 MHz also has better penetration capabilities than 1900 MHz, so cell signals in buildings may be stronger with 800 MHz. If you can find out which frequency your carrier uses in your area, you might be able to discover the reason behind reception issues you're having.
Another factor is the channel-access technology: Some carriers use the GSM ( Global System for Mobile communications ) protocol, while other use CDMA (Code Division Multiple Access ). CDMA broadcasts farther than GSM. In the United States, Verizon, Sprint, U.S. Cellular use CDMA, while AT&T and T-Mobile are GSM carriers; in Canada, Bell, Telus, and SasTel are CDMA carriers; Rogers, Fido, and Wind use GSM. (This, by the way, explains why you can't take your Verizon phone and activate it on AT&T's network: Every cell phone has a radio that works either on GSM or CDMA, but not both…usually.)
These apps will display your cell phone signal strength and other details about your connection.
These links to third-party software are provided "as is" without warranty of any kind, either expressed or implied, and such software is to be used at your own risk. Powerful Signal will not be liable for any damages that you may suffer in connection with downloading, installing, or using such software.
The representatives at Powerful Signal can help you determine why your cell phone signal may not be as strong as you need it, and can help you find a solution to your problem.