How bad is the iPhone 4's signal loss?

    The lower left-hand corner gap. Photo: Apple Inc.

    It's been nearly a week since Steve Jobs famously told a new iPhone owner with reception issues to "stay tuned," but Apple (AAPL) still hasn't solved the new device's Death Grip problem -- its tendency to lose signal strength rapidly when gripped across the gap on the left-hand corner where its two external antennas meet.

    But thanks to some clever work by a pair of engineers at Anandtech, we now have a pretty good idea what's going on when those signal indicator bars start to disappear.

    The report, signed by Brian Klug and Anand Shimpi, the tech site's founder, includes a quantitative analysis of the so-called attenuation -- or signal loss -- that occurs when the device is held four different ways: cupped tightly (the worst), held comfortably in the hand, resting atop a flat open palm and held naturally inside a case.

    The results -- with comparisons to the iPhone 3GS and Google's (GOOG) HTC Nexus One -- are shown in the chart below.

    Source: Anandtech

    As the chart says, small numbers are better; big numbers are worse. But to understand the significance of these results, you need a second Anandtech chart that assigns numerical values in decibels to the bars on an iPhone's display. See below:

    Since decibels are logarithms, a small drop in dB can mean a huge drop in signal strength. -51 dB is the best signal you can get on a 3G network; go beyond -113 and you lose contact entirely. According to Anantech, anything above -107 is usually perfectly fine for voice and data. But even a full five bars can be wiped out by the 24.6 attenuation you get from gripping an iPhone 4.

    "The results are pretty self explanatory," Klug writes about the attenuation chart. "Inside a case, the iPhone 4 performs slightly better than the Nexus One. However, attenuation gets measurably worse depending how you hold the phone. Squeezing it really tightly, you can drop as much as 24 dBm. Holding it naturally, I measured an average of 20 dBm.

    The drop in signal from cupping the device with a case on is purely a function of us being "ugly bags of mostly water." A material which happens to be pretty good at attenuating RF - thus increasing path loss between the handset and cellular base station. There's nothing Apple nor anyone else can do to get around physics, plain and simple. It's something which demonstrably affects every phone's cellular reception.

    But there's a silver lining. The stainless steel band that surrounds the iPhone 4 and serves as its antenna, Klug writes, is better than other cell phones', even with all the attenuation. And when he protected it with a case like Apple's $29 Bumper, he writes,

    "I felt like I was going places no iPhone had ever gone before. There's no doubt in my mind this iPhone gets the best cellular reception yet."

    Given all this, it's surprising that Apple has made it clear in instructions it issued to its telephone reps (and leaked to The Boy Genius Report) that it has no intention of offering free Bumpers to customers who complain about their iPhone 4's signal loss.

    Worse still, for an iPhone 4 owner like myself willing to spend $30 to solve the problem, there are no Bumpers to be had in New York City, not even for ready money.