Sidebar Sidebar
Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.

iPhone 4 reception issues - an alternate theory

L

laser345

macrumors newbie
Original poster
Jun 9, 2008
27
0
Firstly, I apologise if this is mentioned elsewhere. I did of course search with the usual tools but couldn't find anything that seemed to answer my question. Please point me in the right direction if an answer does exist somewhere.

Secondly, the question...

The well publicised reception issues seem to result from touching the black strip on the bottom left corner of the iPhone. This is explained as being a result of bridging the gap between the WiFi/GPS and GSM/UTMS antennae. This being the case, why does bridging the equivalent gap on the top left of the iPhone not elicit the same response? I've tried this several times and can't replicate the problem I myself observe by touching the black strip area on the bottom left.

I'm basing this on the keynote speech where Steve showed iPhone 4's steel band being divided into two different antennae meeting at the bottom left and top left.

My hypothesis, the reception issues are not in fact caused by bridging the gap on the bottom left, but are simply a result of covering the antenna which happens to be located towards the bottom left of the phone.

Thoughts?
 
sensible suggestion although im sure everyone on here will shoot you down straight away because they are all wireless communications engineers and know everything there is to know about the iPhone 4 issue.

Although, as a slight counter argument, why would a bumper solve the problem. Yes obviously the bumper is plastic and probably non-reactive to the electromagnetic waves and therefore it in itself does not cause the problem. But if it was just about covering the cell antenna then surely holding the phone, bumper on, in the same manner would produce the same symptoms, which it doesnt.
 
I assumed that the bumper just acts to move your hand (essentially a bag of conducting liquid) further away from the antenna hence reducing it's ability to interfere with the signal.

Further evidence to support my theory, I tried covering the area around the black strip (bottom-left) with a non-conducting electrical tape and still got the same signal loss when the area was touched. Surely this suggests the problem is not caused by bridging the two antennae?
 
RTigay said:
Because the different sections are different antennas. The bottom left bridges the one that all your cellular data goes through, that's one you really don't want to have not working correctly. The top gap does not mess with the cellular data.
Click to expand...

Surely that can't be true? The steel band is made of two antennae, WiFI/GPS and GSM/UTMS, hence there must be two points where they meet - bottom-left and top-left.
 
laser345 said:
I assumed that the bumper just acts to move your hand (essentially a bag of conducting liquid) further away from the antenna hence reducing it's ability to interfere with the signal.

Further evidence to support my theory, I tried covering the area around the black strip (bottom-left) with a non-conducting electrical tape and still got the same signal loss when the area was touched. Surely this suggests the problem is not caused by bridging the two antennae?
Click to expand...

There are two issues, only one of which Apple is addressing.

1. Brdiging the gap, lengthens the antenna causing it to no longer function properly.

2. The one Apple will own up to and does effect every cell phone to some extent.... Covering the area around the antenna. The more interference you have around the antenna the lower your signal will be.
 
RTigay said:
Because the different sections are different antennas. The bottom left bridges the one that all your cellular data goes through, that's one you really don't want to have not working correctly. The top gap does not mess with the cellular data.
Click to expand...

His point was that whether you bridge the top gap or the bottom left gap, you are still bridging the two antennas.
 
laser345 said:
Surely that can't be true? The steel band is made of two antennae, WiFI/GPS and GSM/UTMS, hence there must be two points where they meet - bottom-left and top-left.
Click to expand...

You are correct. I did make a mistake there, my other post still stands though.
 
laser345 said:
Firstly, I apologise if this is mentioned elsewhere. I did of course search with the usual tools but couldn't find anything that seemed to answer my question. Please point me in the right direction if an answer does exist somewhere.

Secondly, the question...

The well publicised reception issues seem to result from touching the black strip on the bottom left corner of the iPhone. This is explained as being a result of bridging the gap between the WiFi/GPS and GSM/UTMS antennae. This being the case, why does bridging the equivalent gap on the top left of the iPhone not elicit the same response? I've tried this several times and can't replicate the problem I myself observe by touching the black strip area on the bottom left.

I'm basing this on the keynote speech where Steve showed iPhone 4's steel band being divided into two different antennae meeting at the bottom left and top left.

My hypothesis, the reception issues are not in fact caused by bridging the gap on the bottom left, but are simply a result of covering the antenna which happens to be located towards the bottom left of the phone.

Thoughts?
Click to expand...


From what I understand it is MUCH more complicated than that. I read an explanation that was highly complex which I can't find now and unfortunately I am not an RF antenna engineer. But it is something to do with the nodes of an antenna. It is wrong to assume that any point of an antenna is the same. Imagine a standing sine wave. At a node on the antenna you will get peak voltage, which is probably the bottom left. Conversely at another point you will get peak current where the voltage is zero, perhaps the bottom right.

So I am assuming that the point of metal on the antenna where the voltage peak is, is more likely to be affected by the skin contact and bridging to the other antenna.
 
It might be that touching the tip of the antenna can cause problems. On other phones since you can't be sure where exactly the tip of the antenna is it maybe harder to replicate the problem consistently. Either way l still think it's a design compromise that Apple made, not design flaw.
 
laser345 said:
I assumed that the bumper just acts to move your hand (essentially a bag of conducting liquid) further away from the antenna hence reducing it's ability to interfere with the signal.

Further evidence to support my theory, I tried covering the area around the black strip (bottom-left) with a non-conducting electrical tape and still got the same signal loss when the area was touched. Surely this suggests the problem is not caused by bridging the two antennae?
Click to expand...

Signal loss as of BARS or the dBm?
 
jonstatt said:
From what I understand it is MUCH more complicated than that. I read an explanation that was highly complex which I can't find now and unfortunately I am not an RF antenna engineer. But it is something to do with the nodes of an antenna. It is wrong to assume that any point of an antenna is the same. Imagine a standing sine wave. At a node on the antenna you will get peak voltage, which is probably the bottom left. Conversely at another point you will get peak current where the voltage is zero, perhaps the bottom right.

So I am assuming that the point of metal on the antenna where the voltage peak is, is more likely to be affected by the skin contact and bridging to the other antenna.
Click to expand...

This may be closer to the actual situation, do you have a link? Either way, I worry that a lot of people are being misled by the perceived importance of bridging the two antennae at the bottom-left - an act I don't believe is the cause of the problem.

For clarity, here is an image (taken from the keynote) to explain my point.
 

Attachments

  • iphone 4 bridging antennae.JPG
    iphone 4 bridging antennae.JPG
    52.1 KB · Views: 45
nohite said:
It might be that touching the tip of the antenna can cause problems. On other phones since you can't be sure where exactly the tip of the antenna is it maybe harder to replicate the problem consistently. Either way l still think it's a design compromise that Apple made, not design flaw.
Click to expand...

Yes exactly. Do you remember the days of CB radios that kids would play with before the Internet took off? Teenagers would have 30 foot antenna's in their garden and some would put a neon light on it that would glow when they transmitted. As you moved the light up and down the antenna it would either not glow, glow a bit, or glow more brightly, as you hit the voltage peaks along the antenna. Normally the tip was a voltage peak.
 
laser345 said:
This may be closer to the actual situation, do you have a link? Either way, I worry that a lot of people are being misled by the perceived importance of bridging the two antennae at the bottom-left - an act I don't believe is the cause of the problem.

For clarity, here is an image (taken from the keynote) to explain my point.
Click to expand...

I have been searching but I can't find it again yet. I will keep looking.

I do believe the bridging at the bottom left is a partial cause of the problem which combined with the shielding effect, compounds the issue. The reason I say that is because if I just touch my pinky at that bridge I can get the bars to drop quite quickly..and one little finger shouldn't be enough of a shield. If I put a cloth between the metal and my finger, then the signal doesn't degrade at all. If it was shielding, then it would degrade the signal.

Also by sliding my finger down below the bridge, the signal returns...above the bridge...the signal returns...only at the point that I touch both, does the signal drop with one finger.
 
RTigay said:
There are two issues, only one of which Apple is addressing.

1. Brdiging the gap, lengthens the antenna causing it to no longer function properly.

2. The one Apple will own up to and does effect every cell phone to some extent.... Covering the area around the antenna. The more interference you have around the antenna the lower your signal will be.
Click to expand...

Which is funny because when you hold it with your left hand you are only covering the WiFi/GPS/Bluetooth antenna... doh
 
Billy Mays said:
Which is funny because when you hold it with your left hand you are only covering the WiFi/GPS/Bluetooth antenna... doh
Click to expand...

Look at the picture a few posts up from yours...when holding it in the left hand you cover BOTH antennas with the palm of your hand.
 
jonstatt, if you happen to find that article again I would be very interested in reading it.
 
jonstatt said:
Also by sliding my finger down below the bridge, the signal returns...above the bridge...the signal returns...only at the point that I touch both, does the signal drop with one finger.
Click to expand...

Excerpt from a blog explaining your point a little futher:

"Another factor that may affect how much change different people are reporting is that different countries use different frequencies for 3G – AT&T uses 1900 and 850Mhz, (depending on location) while Europe uses primarily 2100Mhz. (With pockets of 900Mhz in a few countries)

At different operating frequencies the standing wave patterns on the antenna elements will be different, leading to certain points on the antenna being more or less sensitive depending on operating frequency. On some operating frequencies the bottom left corner may be an impedance maximum (voltage point) while at other operating frequencies it may not be. Touching a high impedance point of an antenna always detunes it far more than touching a low impedance point."

Source link
 
RTigay said:
jonstatt, if you happen to find that article again I would be very interested in reading it.
Click to expand...

Just found this, HUGE amount of information on wave propagation and antennae in particular. Some light bed-time reading!
 
Interesting....I just realized that you have to cover the entire lower left black strip to lose the connection. If I touch just the side of the strip with a finger (and not touch that tiny band on the top and bottom of the phone, my connection stays solid.
 
There's part of the antenna that connects to the steel band at the bottom left seam:

Steel_Contact.png

Photo courtesy of iFixIt.com

See that brass screw mounting point on the right? That's what brings the larger stainless steel band into contact with the antenna system. Interestingly enough, it's located right where the signal attenuation problems occur! (This is the back of the iPhone, so it's located on the lower right rather than lower left). When you bridge that seam whether it be with your finger or any conductive material, it shorts out the antenna! This is a small enough distance that it has an effect. This would explain why the signal attenuation does not occur at the seam at the top of the iPhone 4, near the headphone jack: because it's too far from this location for the current to be grounded to the Wi-Fi/Bluetooth/GPS antenna. That extra length makes the resistance too high for there to be a significant short across to the other part of the stainless steel band.
 
You must log in or register to reply here.
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.
Top Bottom
Back