Apparently, not very much, at least from an RF engineering viewpoint. Byrnand first identified potential antenna problems in a June 8 post on the Talk3G mobile phone forum. 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 percent of the signal strength from a 3G base station. So those Youtube videos that show the bars disappearing from the iPhone 4 when you hold it…? PCWorld did a pretty extensive, but completely unscientific, field comparison in downtown San Francisco of the iPhone 4 and the previous iPhone 3GS model. The improvement on upload speeds was even more pronounced.

This unscientific trial also specifically looked at what happened to iPhone 4 reception when the reporter held the phone as many do: in your left hand, with your palm covering the bottom left edge of the phone. The number of connection bars dropped from five out of five to only one or two. There are several issues, according to a couple of blog posts by Spencer Webb, the president and principal engineer for AntennaSys, a company that specializes in RF consulting and custom antenna design services.

First, iPhone 4, like almost every other modern cell phone, puts the cellular antennas at the bottom, where they are most likely to be covered by your hand. The reason is that the Federal Communications Commission FCC has strict limits on the amount of energy that can be absorbed by the human body from a handheld device, Webb says in his first post last week.

So the phone designers move the antennas as far away from the head as possible—to the bottom of the phone. Webb says in his post this week that the hand contact has two effects on any antennas. The fact of the matter is that cupping the bottom left corner and making skin contact between the two antennas does result in a measurable difference in cellular reception. But as we'll show, RF is a strange beast.

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When I set out to characterize and understand the iPhone 4's antenna issue, I noticed that reports online varied wildly. Some claimed that they were always able to recreate a reception issue created by cupping the phone, yet others reported no change at all squeezing the phone tightly. It isn't a matter of the dialer code, it's that Field Test has been completely removed from the applications directory in the filesystem. For those that don't know, Field Test variants exist on virtually every phone for purposes of debugging the air interface and baseband.

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Quality metrics like RSSI raw signal strength usually in dBm are reported alongside a wealth of other metrics like SNR and even what adjacent towers are visible to the phone for handing off. It's a tool usually buried deep in every phone because the amount of data would overwhelm normal mobile users, but is useful for engineers and curious but savvy users alike to find out what's going on with the cellular network. For whatever reason, Apple really doesn't want anyone running that tool anymore.

Just about everyone knows that although reporting signal strength in bars gets the job done, it's an absolutely worthless metric for comparison across devices and platforms due to lack of standardization. Further, iOS smoothes the quality metric with a moving average over as much as 10 seconds, masking how fast signal changes. There's also the matter of dynamic range, but more on that in a second.

Without any numbers at all it would've been impossible to understand what's going on with iPhone 4. But I found a way. Undeterred by the lack of field test on iOS 4, I was determined to enable numeric signal strength reporting in the top left where bars are normally displayed. If you've ever run a jailbroken iPhone and used SBSettings, or changed your carrier string, you've probably encountered the fact that iTunes will back up and restore the status bar configuration across OS restores. See where I'm going? I took my iPhone 3GS, downgraded to 3.

I ordered one almost a month ago, but it still hasn't shown up.

The real one is still inexplicably in the mail 15 business days later. Success ensued, and I had a numeric readout of signal strength on a non jailbroken iPhone 4. The results are interesting. Before we dive in, let's talk about dynamic range for a second. For a while, I've talked about how iOS reports the quality metric with a compressed, optimistic dynamic range.

On iOS, 4 bars begins at around to dBm. Three bars sits around dBm, 2 bars extends down to dBm, and 1 bar is dBm. To give you perspective, for a UMTS "3G" plant, dBm is the best reported signal you can get - it's quite literally standing next to, or under a block away from a tower. At the other extreme, dBm is the worst possible signal you can have before disconnecting entirely. With a few exceptions, signal power as low as dBm is actually perfectly fine for calls and data, and below that is where trouble usually starts.

How I recovered my iPhone's lost GSM signal!

However, you can see just how little dynamic range iOS 4 has for reporting signal; over half of the range of possible signal levels in dBm from dBm to dBm is reported as 5 bars. So, an entire day and more than a quarter tank of gas later, here are the results. Holding the iPhone 4 without a case, in your left hand, crossing the black strip can result in a worst case drop of 24 dB in signal.

As we'll show in a second, how you hold the phone makes a huge difference across every smartphone - and we've tested thoroughly in 5 different positions. Now, there are two vastly different possibilities for what happens to the bar visualization after you drop 24 dB.

Signal is above dBm in every single room, in most cases it's at dBm. When I incur that worst case drop of 24 dB from squeezing the phone, I fall down to dBm, which is still visualized as 5 bars. However, in locales that have less signal, but where iOS still displays 5 bars, the drop of 24 dB is visualized much differently.

For example, at another test location, signal without holding the phone is dBm, which is still displayed as 5 bars. Cup the phone, and you'll fall all the way to dBm.

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All the bars dramatically disappear one after the other, people think they've dramatically lost all the signal, and you know the rest. If you're at 4 bars already, which puts you on the low end of possible signal strengths , cupping the phone even more delicately is enough to push you the remaining 10 or so dB to cutoff.

If that is the case, we can help you replace the LCD as well. Symptoms of a defective or busted LCD can include lines through the display, lots of dead pixels, a white screen, black screen, or extremely dim screen. In some instances, you can see discoloration or bleed spots in the display. Considering the iPhone 3G and iPhone 3GS are both a few years old now, many users experience drastic battery loss after so many charge cycles.

Whether your iPhone is dying quickly or refuses to hold a charge anymore, a replacement battery can breathe plenty of new life into it. Symptoms of a dying battery can include short time spans off a charger before dying and in some instances, the iPhone won't boot up at all. If you're experiencing any of these, it's time to replace that battery. The induction flex is what controls your auto brightness ambient light sensor and proximity sensor. If your phone refuses to dim when auto brightness is activated or the screen doesn't turn off when it's against your face causing you to press buttons unintentionally while on a call, putting a new induction flex in can solve the issue.

The earpiece speaker is located inside the top of the display and is what you hear callers out of when on a call. If the earpiece has stopped working or creates bad feedback including high pitched tones, garbled audio, or low volume regardless how high you turn it up, it's probably time to replace it. The repair isn't too time consuming and will get your iPhone 3G or iPhone 3GS call quality back to where it should be in no time. Vibrator assemblies run on motors and occasionally those motors can burn out over time.

Whether your iPhone 3G or iPhone 3GS isn't producing vibration alerts at all anymore or they seem really faint, a new vibrator assembly can get you back to working order. Note: The 3GS in particular is prone to issues with the vibrator switch. This is not the same as the assembly. The switch issue typically is caused by a bad cable in the top left corner. Symptoms of this problem can be unwanted vibrations when pushing in the upper left hand corner of the iPhone. We'll have a guide coming on this in the near future.