Blog Post

iPhone 4 Attenuation Only Half the Story

Something about Apple’s press conference yesterday just didn’t sit right with me. Apple (s aapl) has put up a page with videos of various other smart phones displaying the same type of behavior when griped in a certain way. It also has put up a page where its explains its $100 million dollar testing facilities it uses for testing reception and signal in various conditions, just to let us know how much the company cares. Steve Jobs said that they love us. They seem to be doing the right thing by giving out the free bumper cases, but how they explained why the cases are needed in some instances didn’t quite cover everything. Attenuation is only half the story.

Way back when, a couple of lifetimes ago, I was a Radioman in the Navy, and as part of my education and advancement requirements I had to study antenna and wave propagation theory. For the sake of brevity, I’m going to over-simplify this to the point where real engineers might get a headache if they continue on, but here goes anyway.

Radio signals traveling through the air look like waves if drawn on paper. These waves travel at a constant speed, the speed of light, so to send more waves through on a signal, the waves must be smaller. The number of waves traveling along a signal is referred to as hertz, and the size of the wave is its wavelength. The antennas used to generate and receive these waves need to be the right size, and the right shape. Back when I was in the Navy, we were transmitting waves that required a 35 foot whip antenna because we were transmitting in the High Frequency (HF) range. As the frequency of the wave gets higher, the size of the waves and the antenna used to transmit and receive them become smaller, and more precise.

Cell phones operate in the Ultra High Frequency (UHF) frequency range, so the antenna that they use is much smaller than lower frequency transmissions. The iPhone 4 has two antenna that wrap around its case, one for cellular use and the other for Wi-Fi and bluetooth. The two antennas are separated by the small gap in the lower left hand side of the case, which Apple has identified as the antenna’s most sensitive part. This is true, in part because of the attenuation (or “blocking of the signal”) when you put your hand over the gap.

The other part of the equation that Apple is not talking about is that while your hand doesn’t make a particularly good medium for radio waves to travel through, it does make a fairly good electrical conductor. When you place your hand over that gap, you are actually bridging the two antennas together and making a larger antenna. A larger antenna that is not the right size for the frequency of AT&T’s cellular network, and the bars drop right off.

I don’t have the equipment on hand anymore to test this, but the video below, linked to by an expert on antennas (via Daring Fireball), seems to show the behavior I would expect. At around the 1:30 mark, a key placed over the gap drops the iPhone 4’s reception down from five bars to one, and the narrator says that eventually there will be no signal at all. When the key is removed, the bars return.

The free bumpers solve both problems for the iPhone 4. They prevent the antenna gap from being bridged by anything conductive, and they give a little more room between the antenna and your hand, to help with attenuation. Unfortunately, the bumpers do not address the actual design of the antenna. It may be possible for Apple to move the antenna gap to a different spot on the phone in future revisions of the iPhone. For example, why not put the antenna at the top of the phone where people are less likely to hold it? As answered by AntennaSys in the link above, physical placement of the antenna is mandated by the FCC. If bridging the antenna gap is the problem, it may be possible to move the gap to the bottom of the phone, but since that would change the shape of the antenna, I’m not sure if that’s possible or not. Anandtech has a beautiful solution using Kapton insulating tape, which makes the iPhone look like it’s been plated in gold. If Apple were to add a layer of insulation to the iPhone, that might alleviate the symptoms.

I’m not the only one who thought that Apple’s explanation seemed lacking. TidBITS writer Rich Mogull has a very detailed article where he draws a similar conclusion. If you’d like to know more about the issue, I’d suggest dropping his article into Instapaper. If you’ve got any ideas about the iPhone 4’s antenna “situation,” I’d love to hear from you in the comments. Especially if anyone can reproduce the key trick from the video.

76 Responses to “iPhone 4 Attenuation Only Half the Story”

  1. Hi guys! I’ve recently found this cool I-shop on the internet, called . It is based in UK and sells inexpensive good quality micro sim adapters and UNIQUE Idecal cases that Insulate iPhone 4 antenna, which reduce signal loss, and protect iphone 4 metal band from scratches. Highly recommend it!

  2. Geetika

    I am a first time apple user. I had always wanted an iPhone and now when I get one it has become my biggest nightmare. First I waited for my iPhone everyday for a month absolutely understand since new iPhone is so in demand. When i finally get it 2 days ago I realize I cannot get it to work. After several hours with AT&T my phone finally gets activated and then I find out that I cannot hear anyone on the other side and when I put the speaker phone on no matter if i keep it on the table or which way i hold it after a sentence I stop hearing the other person. Ok so I call AT&T all this after several hours have passed they tell me they cannot help. I ordered thru premier site so i have to call them. So i get on the phone and again after speaking to several people they cannot suggest a way to exchange a phone. They tell me I would be charged full amount$600 for the new phone and if and when i return the other iPhone and if they feel the other iPhone has a problem then they will reimburse me the money for the second I phone but there is no guarantee as the phone is too much in demand so essentially I could get stuck with 2 phones with technical difficulties one where i am stuck in a two yeR contract and the other where i have paid the full amount. And all this because they tell me that this problem is a very common problem with all I phone,s not to mention the amount of other problems iPhones are having so my question is why sell them? If you cannot get something as basic as Call clarity then why sell them at all. Even the phones wih no brand sold in china do not have such basic problems. So after all this when i do call the apple store to see if they can help me they discourage me as much as tehy can and tell me they can look at the problem but i cannot get an appointment before several days. And guess what something that i always dreamt to have now has become my biggest problem. I hope someone has warned me about the new phones followed by the bad customer service.

  3. Hamranhansenhansen

    > I don’t have the equipment on hand anymore to test
    > this, but the video below, linked to by an expert
    > on antennas (via Daring Fireball), seems to show
    > the behavior I would expect.

    A major problem with this issue has been people looking at videos that “seem to show” something or other. Is this video in a 1900MHz cell, or an 850MHz cell? The 1900MHz cells are easier to block with a wall or hand, they were designed only to be used outdoors. There is way too much complexity for YouTube to be helpful at all.

    Me and my friends are having no trouble with iPhone 4. We find it has better reception than previous iPhones. And none of us have cases.

  4. Some people continue saying that the hand is not a very good conductor. While that may be true, it explains why holding the iPhone 4 so that your hand bridges the small gap in the lower left will cause the antenna to change its characteristics. If the hand were a good conductor, then it would not matter where you hold the iPhone 4, you would make a connection between the antenna segments. Take a piece of copper wire or other conductor and touch the opposite sides of the phone with the bare ends. The same drop in signal will occur. The key is only a convenient conductor. And all of this I have discussed since that notoriously long MacRumors article with its 2500-plus postings more than a week ago.

  5. Hashish al-Jihadi

    Okay let us stop beating this dead horse already. Steve has spoken. Antenna-Gate is officially OVER !
    Next iteration of iPhone will get antenna redesign because it is required for LTE radio. So this will soon be totally forgotten once we all move rapidly to 4G (WiMax -or- LTE).
    Bumper Case was an awesome and cheap solution, no recall was needed, Steve is hero once again, next iPhone will be even better, nobody returning iPhone4 because alternative phones are inferior. IT’S ALL GOOD PEOPLE. SHALL WE MOVE ON THEN. LET’S GO. I WILL SEE YOU ON THE OTHER SIDE.

  6. Apple still hasn’t got the guts to admit that they really screwed up.

    Instead, they adjust their software so that you don’t see the bars dropping any more.

    To bridge the gap until everyone has the 4.1 software, they give out free bumpers until september.

    Way to go Apple… you’re just lucky that the competition is still so far behind. In a year or two, this kind of screwup will really cost you…

  7. I don’t have an iPhone 4. Not yet. I’m bound to go for one once it is released over here in Switzerland. The past few weeks and the discussions in the US have offered me with quite some insight about the whole antenna issue. Now, don’t slate for coming across as slightly ignorant or foolish, but when you have a cell phone that sells more than one and half a million within the first two weeks of its release and then see an inofficial (?) number of 16’000 people having problems with the antenna and/or reception, it baffles me how so many tech sites can “make an elephant out of a fly” like we tend to say over here. Yes, it is an issue. To some. But the heated way this is being discussed and the coverage it is getting has me chuckling. Yes, I do expect Apple to come out with great products every year or so. But they’re not perfect. You can have the smartest bunch of engineers in the room (like the many PhD’s in Cupertino), they’re still prone to errors. Criticism where criticism is due, but keep it fair, peeps – like others have stated, I’d love to see more of Apple’s competitors’ products flaws exposed, as well. The way some bloggers and tech-nerds are dissecting every screw and chip in the iPhone borders on the obsessive-compulsive. I’d also like to point out that some, yes SOME, of the problems surrounding bad reception very probably also have to do with AT&T’s network coverage, which from my own experience, can be laughable at times. And they haven’t been there since yesterday. In these turbulent times, what strikes me most -and this is a more general observation – is that phones, like many other gadgets or accessories, are supposed to supplement a certain lifestyle or image and if the accessory suddenly doesn’t live up to the (high) expectations, especially with Apple because they’re oh so trendy if you want to believe the hype, it’s treated like a new form of a venereal disease – and people should be more concerned about the latter, really. Some folks just don’t seem to get their priorities right these days. Relax. Get a grip. Or get a free bumper.

  8. It gets boring! I can’t hear it anymore. I didn’t buy an iPhone (because of the carrier-enforcement), but I tested my Sony Ericsson Naite. Guess what: Apple is right. It’s the same with a non-iPhone.

    So please – stop that ennoying “news” about the iPhone antenna. If someone don’t like it – bring it back (jep, like in that song). I would like to read something new here besides.

  9. Apple does the only logical thing: solving the antenna problem for current iPhone owners (problem perceived, real, or imposed on you by media) and shutting up about future redesign. Talking about a redesign being around the corner would severely reduce sales, to state the obvious. And that would be pointless for the best gadget ever made. And for most of us, the best mobile phone as a phone we’ve ever had.

  10. Crusader

    My god some of you people are just missing the point. Apple products are supposed to *just work*, period. If I’m feeling anxious about using an iPhone 4 then Apple has seriously failed and that quality issue need to redressed. Not calling people names or “fandroids” or any other such nonsense. There is nothing magical about wondering if holding the phone in the “wrong” way is gonna drop your call.

  11. Wow, what a response! I hope I’ve answered most of your questions in my replies to your comments. I admit that it’s been a long time since my radioman days, and it’s quite possible that my theory is wrong. What I was hoping to spur here was a technical discussion about cellular antennas, their design, and how placing the iPhone 4 antenna on the outside of the case affects its use. Thank you all for taking the time to respond and share your thoughts.