Our iPhone 4 Signal Strength Tests

Does holding the iPhone 4 in the infamous 'death grip' actually affect signal strength or is it just a software bug, as claimed by Steve Jobs? Everyone seems to have their own word to say on the Antennagate issue, in what seems like a collective attempt to shoot Apple down. As several experts have now published tests confirming a hardware fault, we thought it was about time we tested the iPhone 4 for ourselves.

Software bug or hardware fault? DigitalVersus investigates!

The iPhone 4 drops signal strength when held in a certain way. Steve Jobs claims this problem results from a software bug that misrepresents the number of bars' signal strength. Last week, Apple released a software update (iOS 4.0.1) to correct 'the formula to determine how many bars of signal strength to display'. However, many experts, journalists and users have published tests that apparently prove that the problem stems from the phone's hardware rather than its software. The test published by the American consumer magazine Consumer Reports was particularly damning.

In our test of the iPhone 4, Florence Legrand reported that covering the 'danger zone' on the outer edge of the model we tested (effectively covering the small gap between the two antennae) never caused the iPhone 4 to drop a call. However, in the interest of publishing our test in a timely manner, we didn't get chance to investigate the problem further and in a quantitative manner. So, to get to the bottom of things once and for all, we've gone out and bought ourselves a second iPhone 4 from the SFR* shop (thanks Val). Let the tests commence!

*Note that SFR is basically the French equivalent of Vodafone (although owned jointly by Vodafone and Vivendi), as, for those of you who didn't know, our offices are based in Paris.

Problem: to what extent does holding the phone affect the connection bitrate?

To go about answering this question, we downloaded 1300 KB files at least three times in eight different test scenarios, based on different phone grips or locations. The two locations we used were the 4th floor of our Paris offices, where network reception is excellent (you can even see the GSM/3G aerials outside), and then shut inside the brand new sound studio (walls 30-40 cm thick) on the 3rd floor, where signal strength is much weaker.

The insulated sound studio

Results

Key:

• 3rd = test carried out in the sound-insulated studio on the 3rd floor.
• 4th = test carried out on the 4th floor with good network reception.
• The number before the B is the minimum number of bars displayed on-screen during the test.
• Normal = not touching the phone.
• Left = holding the phone in the left hand, covering the gap.
• Right = holding the phone in the right hand, not touching the gap.
• Paper clip = a paper clip stuck over the gap connects the two antennae.
• Tape = a bit of sticky tape stuck over the gap.
• 4th left 4B vs 4th left 3B: for the 4B test, we picked up the phone in our left hand as soon as the download started. For the 3B test, we had been holding the phone in our left hand for 1 minute before starting the download.

 

Observations

• With good signal strength: whether holding the right or left side of the phone or not touching the iPhone at all had no real affect on the bitrate when downloading files. Although not shown in the graph, we also saw that the Bumper had no impact on signal strength in good conditions.
• With poor signal strength: holding the palm of our hand over the gap for extended periods of time caused the bitrate to fall by 60%.
  

Interesting stuff, but what does it mean in real terms? Time for a few questions and answers.

Does the bitrate change when your hand covers the gap?

Yes, but only if the signal strength is poor or low to start with. In good conditions, like the 4th floor of our offices, placing the palm of your hand over the gap can sometimes affect the number of bars displayed on the screen, but the bitrate when downloading isn't affected. In our tests it remained between 130 and 160 KB per second.

However, when signal strength is low, like in our sound studio on the 3rd floor, and when keeping the palm of your hand pressed firmly against the gap, the download bitrate can drop. In our tests it fell to 60 KB per second, which makes for a drop of around 60%.

Is the bitrate proportional to the number of bars on- screen?

Yes, pretty much.

With only one bar of reception displayed, the connection wasn't very fast and the files sometimes stopped downloading completely.

With two bars, the bitrate climbed to between 55 KBps and 85 KBps.

With three, four or five bars, downloading took place at around 150 KB per second. In fact, we didn't notice any variation in speed between these three signal strength levels. However, this bitrate 'plateau' could be caused by restrictions imposed by the network operator. We'll try having a go with another iPhone 4 on a different network to see if we can get better results with four and five bars' reception.

Did holding the phone cause the connection to drop out completely?

Within the half-metre-thick insulated walls of our sound studio, all housed within our regular office walls, the network reception bars dropped down to two, sometimes even one, after covering the gap with our hand for around twenty seconds.

Very short signal drop-outs made the bitrate half as slow, but we still managed to download the files nearly every time. We actually carried out this test around fifteen times rather than just three times. The file failed to download twice.

Our tests therefore show that covering the gap does cause a drop in signal strength if the network coverage conditions aren't good to start with.

Does covering the gap with a bit of sticky tape fix the problem or make things worse?

It didn't change anything on our model.

And now, ladies and gentlemen, it's the moment you've all been waiting for, the £1m question ... is it a software bug or a hardware fault?

So is this problem caused by a 'software' bug that could potentially be corrected by iOS 4.0.1? The fact that the bitrate didn't change at all whether we had three, four of five bars of signal strength could suggest this. However, this can also be due to the fact that three bars' reception is enough to attain the maximum bitrate authorised by the network operator. To be honest, this seems like a more likely explanation to us, especially as with one or two bars' reception, the bitrate drops significantly when downloading (by 60% and 40% respectively)!

So with a signal strength that can be considered 'poor', our tests showed that the way you hold the iPhone 4 does affect the handset's network connection. But is the iPhone 4 affected to a greater extent than other handsets? That's something we'll test at a later date. For the moment, all we can say is that our tests point to some kind of hardware fault. Whether this fault is specific to the iPhone 4 or widespread in the market, as suggested by Steve Jobs, remains to be seen. Confusion seems to be mounting as some sites have recently published extracts from Nokia's user manuals telling users that covering the antenna can cause performance issues. In any case, we'll be carrying out tests on a selection of other mobile phones over the weekend to help us draw our own conclusions on the matter.

Conclusion

Based on the results of our tests this looks like a hardware fault rather than a simple case of 'phantom' signal strength bars.

Consumer Reports says it can't recommend the iPhone 4 to its readers. Does DigitalVersus think the same? Will DV continue to recommend the iPhone 3GS over the iPhone 4?

No, we won't be doing that. Our test results simply don't allow is to draw such a harsh and clear-cut conclusion. Plus, we like the iPhone 4 for its increased battery life, enhanced photo capabilities, HD video mode, improved responsiveness and sleek design ...

> Review: Apple iPhone 4

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