The external metal casing of the iPhone 4 also acts as an antenna. Users quickly found out that by covering up the slit in the bottom left side of the device they could reliably reduce the signal drastically, and often even make calls drop. Countless videos showing the problem at work popped up all over the web.
Apple has been remarkably dismissive. Via Steve Jobs' infamous emails, users were told to "hold the phone differently" or to buy those bumper cases (which Apple conveniently introduced alongside the iPhone 4...). On top of that, Jobs is stating that the entire issue is nothing more than "a few days of rumours" - while at the same time stating the company is "working on it". Mixed signals, bad PR. Maybe it's time to close that email address for at least a little while.
In any case, we didn't really have any proper testing done on this antenna issue. The problem is that those bars denoting signal strength are a bunch of arbitrary hocus-pocus, and don't really indicate anything meaningful when comparing different make/model phones. Luckily, the guys and girls at AnandTech got to work, and found a way to properly test the iPhone 4's reception.
AnandTech's Brian Klug and Anand Lal Shimpi managed to enable numerical signal strength reporting (dB) on the iPhone 4, and compared this figure with a 3GS and Nexus One while holding the phones in several different ways. They conclude that the iPhone 4 can suffer about 20 dB signal loss when held comfortably, and 24 dB when held very tightly (but this is uncomfortable). The 3GS suffers from far less signal loss (about 1.9 dB signal loss when held comfortably), whereas the Nexus One sat somewhere in between (10.7 dB signal loss when held comfortably). Remember that this is a logarithmic scale.
From these measurements, AnandTech concludes that Apple should either cover the antenna with insulative coating, or supply free bumper cases (which reduce the problem significantly). "For a company that uses style heavily as a selling point, the latter isn't an option," they write, "And the former would require an unprecedented admission of fault on Apple's part."
This is only half of the story, though. AnandTech also found out that while the iPhone 4 suffers from its external antenna design, it also benefits greatly from it. In areas with very low signal (-113 dBm), the iPhone 4 performs much better than the iPhone 3GS. "I can honestly say that I've never held onto so many calls and data simultaneously on 1 bar at -113 dBm as I have with the iPhone 4, so it's readily apparent that the new baseband hardware is much more sensitive compared to what was in the 3GS. The difference is that reception is massively better on the iPhone 4 in actual use."
So, this new antenna design and improved baseband hardware is a double-edged sword, AnandTech concludes.
"The drop in signal from holding the phone with your left hand arguably remains a problem," they write, "Changing the bars visualization may indeed help mask it, and to be fair the phone works fine all the way down to -113 dBm, but it will persist - software updates can change physics as much as they can change hardware design. At the end of the day, Apple should add an insulative coating to the stainless steel band, or subsidize bumper cases. It's that simple."
Finally, some good and well-done measurements of this problem. The web has been tumbling over itself about this problem ever since the iPhone 4 first made it into testers' hands, but I was reluctant to write about it until we had some actual hard science to actually qualify the problem.
Now that we do, the issue has become a lot clearer: there is a problem with the iPhone 4, but it's not as bad is some people make it out to be. Still, this problem is a design flaw, and Apple should do something about it. Steve Jobs declaring it all simple rumours really isn't doing the company any favours here.