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Network World - If I buy an iPhone 4, am I going to have big radio frequency reception problems, apart from being on AT&T's network?
It depends on how you define "big" and on a whole bunch of other variables, such as what 3G frequency you're on, maybe your body mass index and even whether your hands are sweaty. There have been a rash of complaints from new iPhone 4 users that when they wrap their hand around the phone to take or make a call the phone's signal strength indicator -- those bars on the screen -- can show a big drop.
What do those bars actually mean?
Apparently, not very much, at least from an RF engineering viewpoint. There's been an interesting discussion online about this issue. The consensus is that Apple's bar display of signal strength is highly relative: it's actually showing only a small part of the lowest end of possible signal strength, according to two bloggers, Steve Gibson, and Simon Byrnand. (Byrnand first identified potential antenna problems in a June 8 post on the Talk3G mobile phone forum.)
That seems weird, doesn't it?
Keep in mind that the five-bar display -- and this is true for all cell phones, not just iPhone 4, according to Byrnand -- is in effect "only supposed to give a relative indication of likely call quality -- any signal stronger than 5 bars whilst stronger, won't lead to better call quality so [it] isn't indicated to the user to keep things simple," he writes.
(According to Byrnand, the iPhone operating system used to have a very detailed signal strength reader, a hidden app that was activated by dialing a specific numeric string and capable of showing the exact received signal strength in –dBm. But it was removed from an early beta version of iOS 4.)
To get a good, clear conversation, Gibson says, you might only need 5% of the signal strength from a 3G base station. So the "5-bars" covers any signal strength from 100% down to 5%. "It's only when the received signal strength begins to drop below 5% that conversations suffer, calls get dropped, and Apple starts to take bars away from their 5-bar display," Gibson writes.
So those Youtube videos that show the bars disappearing from the iPhone 4 when you hold it...?
Gibson speculates that in those videos, the phone's signal strength is actually very, very low to begin with. So when you cover the antennas with your hand, or when your skin "bridges" the cellular and Wi-Fi antennas, it's enough to cause the signal to drop still lower, and that's when Apple's "five bars" becomes "three bars" or two or none.
So what's actually happening?
First, keep in mind that with iPhone 4, Apple integrated several antennas into the exterior stainless steel band around the phone's edge, which is "cut" in three places by a dark slot of insulation. During the phone's public unveiling, Apple claimed that moving the antennas to the outside of phone would actually improve reception.
It seems so, though other factors are involved, including the use of a glass back for iPhone 4 instead of the plastic in the 3GS model, and AT&T's ongoing cellular upgrade to High Speed Packet Access (HSPA). One blogger, an antenna design specialist named Spencer Webb, says the design change "probably improves" the uniformity of the antenna's radiation pattern "but only when the phone is suspended magically in air.”