An explanation of why not all phones show bars the same way
It is easy to assume that different phones show you the same number of bars for the same signal strength, but it is not always true. Let us discuss how Apple iPhone and an HTC Android both display signal strength bars differently.
The number of bars on your phone are affected by more that just the signal strength. Each cell tower is shared by many users and the more people that use the tower, the lower the signal quality and this is called channel loading. Imagine you're in a crowded room and you're talking to a friend of yours. Their voice is the signal level that you try to listen to, but the voices of all the other people would represent channel loading. If your friend is speaking loudly, but so is everybody else in the room, then the channel loading is high and you still may not be able to hear them, but if your friend is whispering and everybody else is quiet, you might be able to hear them pretty well against the silence. Effectively this is like having very low channel loading.
To see the effects of channel loading and signal level, we can use a piece of test equipment to simulate the cell phone tower. For signal strength, we will adjust the pilot power or C-pitch. For channel loading we will adjusting ECIO. First off, we're going to try the HTC Android phone. When adjusting the signal level, it is easy to see the number of bars changing on the phone. Now we can go from the low channel loading to the high channel loading and we will adjust the signal level on the test equipment. Now we see that the number of bars seems to be tracking the signal level. It doesn't seem to care what the channel loading level is on the HTC. This gives me confidence that the number of bars I'm seeing is representative of the signal level the phone is receiving.
Alright, now we can try the iPhone. Upon changing the signal strength you will see that we do not see the number of bars change on iPhone. Now lets see what happens when we change the channel loading but not change the signal level at all. We have to wait a couple of minutes because the iPhone can take awhile to update the number of bars on the display sometimes. Thereafter, the number of bars drops, showing us that the iPhone is influenced by channel loading. Just to be safe, we will take the power level down and then we will take it down again and you will see that the number of bars displayed on the phone don't change. This tells us that iPhone cares more about channel loading than it does the actual level of signal that it is receiving.
If you would like to see an accurate measure of signal strength on your iPhone, put it in the test mode, tap on the number of bars to get the numeric signal level displayed. We suggest putting in a phone call and that way it will update more quickly. Now that we have the phone in the numeric power level mode, you will see the number drop as we drop the signal level, which is just what we want it to do. It is a negative number. The closer to zero, the stronger the signal. The closer to say -100, the lower level the signal. It is showing us the real power level is exactly what we want. Now we will bring the power level back up a little bit. Again it tracks exactly the way we want it to. This shows us how different phones can calculate the number of bars to display very differently. The HTC Android shows us the actual signal level, while the iPhone favoured the channel loading.