Why your new iPhone may see different signal levels as compared to an older iPhone or a different cell phone

Many people, upon purchasing a new iPhone, are surprised when they do a comparison and either see different signal levels on their new iPhone as compared to their old iPhone or as compared to a friend's Android device.

While there is some variation that comes down to antenna designs, most often this is due to the way the antennas on your local cellular tower are configured and calibrated.

I'll give an example using the US model iPhone and FDD-LTE frequencies; these are the frequency bands supported by three recent devices:

• iPhone 11: FDD‑LTE (Bands 1, 2, 3, 4, 5, 7, 8, 12, 13, 14, 17, 18, 19, 20, 25, 26, 29, 30, 66, 71)
• iPhone 12: FDD‑LTE (Bands 1, 2, 3, 4, 5, 7, 8, 12, 13, 14, 17, 18, 19, 20, 25, 26, 28, 29, 30, 32, 66, 71)
• iPhone 13: FDD-LTE (Bands 1, 2, 3, 4, 5, 7, 8, 11, 12, 13, 14, 17, 18, 19, 20, 21, 25, 26, 28, 29, 30, 32, 66, 71)

I've emboldened the differences between the iPhone 11 and 12, and bold/italicized differences between the iPhone 12 and 13.

When your device first communicates with a cell tower, it introduces itself and says "Hi, I'm here now."

The base station controller at the cell tower says "Great, you're an iPhone 13, let's see, you support FDD-LTE frequency band 21. That band is less congested than others because only newer phones support it, so use frequency band 21."

Now, if the cell tower is poorly optimized for operation on frequency band 21, your iPhone 11, which might be assigned to frequency band 17, could show full bars while your iPhone 13 has poor reception on band 21.

Your iPhone 13 can't just unilaterally decide to use band 17, the cellular network doesn't work that way.

This would result in your iPhone 13 having poor signals and perhaps even dropping calls where your iPhone 11 would work perfectly, all through no fault of your iPhone 13.

Further, you can't directly compare and say "My iPhone 11 shows four bars of signal while my iPhone 13 shows two" because bars are relative according to each phone's radio capabilities.

For example, for a signal level of -50 dBm (levels typically range from around -30 dBm to -110 dBm with values closer to zero being stronger) a device that couldn't properly handle any signal stronger than -40 dBm might show that level as "full bars," where one that could handle signal levels to -20 dBm might show it as perhaps just two out of four bars.

In a very real way, any cell phone is just a radio transmitter/receiver designed to meet certain specifications, and just as an FM radio tuner is no better than the signal broadcast by your local station, your iPhone can't compensate for any deficiencies in your carrier's cellular network.