Yesterday I read an article on the BBC website about the letter Apple have issued regarding the reception issues with the iPhone 4. When I read the letter I was immediately suspicious about their intentions to release a software fix that would try to fix what appeared to be a hardware interference issue.

Here is a summary of what I have learned about the issue:

1. Apple have admitted that holding the iPhone 4 causes reception issues:

Apple: To start with, gripping almost any mobile phone in certain ways will reduce its reception by 1 or more bars. This is true of iPhone 4, iPhone 3GS, as well as many Droid, Nokia and RIM phones.

2. Field Test, an application to measure signal strength (RSSI) and other quality metrics (including SNR) has been removed from the iPhone 4 (and iOS4). Yet it was available for the 3GS.

3. Reception measured in bars is not standardised – it varies by manufacturer – thus 5 bars on one phone does not correspond to the same signal strength or quality as 5 bars on another. According to the findings reported in this article on AnandTech the iPhone bars correspond to the following signal strengths:

5 bars: -99 dBm to -51 dBm (best reported)

4 bars: -101 dBm

3 bars: -103 dBm

2 bars: -107 dBm

1 bar: -113 dBm (lowest without disconnecting)

Notice that over half the range is attributed to 5 bars. You could argue that this was done as a marketing ploy to demonstrate how good the reception was on the phone. Note what Apple said in their letter:

Apple: Our formula, in many instances, mistakenly displays 2 more bars than it should for a given signal strength…

Users observing a drop of several bars when they grip their iPhone in a certain way are most likely in an area with very weak signal strength, but they don’t know it because we are erroneously displaying 4 or 5 bars. Their big drop in bars is because their high bars were never real in the first place.

And they confirm that the fake bars will now be replaced with larger bars to maintain the feeling you have great reception…

Apple: We are also making bars 1, 2 and 3 a bit taller so they will be easier to see.

4. Although Apple won’t admit it, the antenna design is flawed when considering signal strength

Apple: some users have reported that iPhone 4 can drop 4 or 5 bars when tightly held in a way which covers the black strip in the lower left corner of the metal band. This is a far bigger drop than normal, and as a result some have accused the iPhone 4 of having a faulty antenna design…

We have gone back to our labs and retested everything, and the results are the same— the iPhone 4’s wireless performance is the best we have ever shipped.

Whilst Apple say the wireless performance is the best they have ever shipped, the signal attenuation is considerably worse than the 3GS:

AnandTech: 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.

The article reports that the worst attenuation with the 3GS was 14.3 dB

AnandTech: Holding it naturally, I measured an average drop of 20 dB.

In this case, the article reports that the attenuation for the 3GS was 1.9 dB and goes on to state that for the antenna to be effective in it’s current design it should have had an insulative coating or a case.

AnandTech: The fact of the matter is that either the most sensitive region of the antenna should have an insulative coating, or everyone should use a case. For a company that uses style heavily as a selling point, the latter isn’t an option. And the former would require an unprecedented admission of fault on Apple’s part.

On a similar note, BBC News quotes Stuart Miles:

Why, for the first time, has Apple released a bumper for their phone…?

5. However, the Signal to Noise ratio has improved:

AnandTech: From my day of testing, I’ve determined that the iPhone 4 performs much better than the 3GS in situations where signal is very low, at -113 dBm (1 bar). Previously, dropping this low all but guaranteed that calls would drop, fail to be placed, and data would no longer be transacted at all…

It’s readily apparent that because the iPhone 4 works almost perfectly fine at -113 dBm, it has much better sensitivity. The deciding factor for reporting the signal quality metric is then SNR, something Apple and other handset manufacturers will have to move to eventually instead of just power.

I believe this is what Apple are referring to in their letter:

Apple: we continue to read articles and receive hundreds of emails from users saying that iPhone 4 reception is better than the iPhone 3GS.

Conclusion

In summary it appears that whilst the Antenna design is a step forward in terms of sensitivity and reduced SNR, the lack of insulation results in reduced signal strength when the phone is held. This will remain a problem regardless of how many bars are displayed on screen after the software update.

AnandTech: 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.

Of course if your not happy you can always return it and buy an HTC Desire!

Apple: For those who have had concerns, we apologize for any anxiety we may have caused……you can return your undamaged iPhone to any Apple Retail Store or the online Apple Store within 30 days of purchase for a full refund.