As part of its iPhone 4 review, AnandTech took an in-depth look at the iPhone 4’s antenna and its signal issues, finding that “cupping the bottom left corner and making skin contact between the two antennas does result in a measurable difference in cellular reception,” but adding, “RF is a strange beast.” According to the review, standard signal strength for a UMTS 3G phone can range from -51 dBm—standing underneath or extremely close to the tower—to -113 dBm, the lowest amount of signal the phone can have before disconnecting entirely. Interestingly, AnandTech found that the iPhone 4’s bars map signal differently than one might expect, with more than 40% of the range of possible signal levels—from -99 dBm to -51 dBm—reported as five bars. The four bars indicator begins at roughly -99 to -101 dBm and three bars at -103 dBm, with two bars extending down to -107 dBm, and one bar covering all signals lower than that.
Based on AnandTech’s tests, the iPhone 4 exhibits a maximum signal drop of 24 dBm when held in the left hand and crossing the black strip at the bottom with the palm. When held naturally, but without making contact with the open palm, a drop of nearly 20 dBm was seen; when held naturally inside a case, that number dropped to 7 dBm. For comparison, the iPhone 3GS experienced drops of 14 dBm, 1.9 dBm, and 3.2 dBm, while the Google Nexus One scored losses of 18 dBm, 11 dBm, and 8 dBm, respectively. Despite the drops, the review finds that the iPhone 4’s antenna is actually improved from the iPhone 3GS, with the new handset showing an improved ability to perform calls and receive/send data when at the one bar signal level, and when encased, it was able to find and/or hold on to a signal in spots where the iPhone 3GS failed to find to do either.