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Signal mysteries finally solved.

L

LobsterDK

macrumors member
Original poster
Jun 24, 2010
69
0
In case everyone hasn't read it yet, Anandtech has a review of the iPhone with a detailed signal strength analasys. This makes things so much clearer. The dBm to bar scale chart is about midway down the page.

http://www.anandtech.com/show/3794/the-iphone-4-review/2


The bar display "bug" was really screwing people up and distorting their perception on what was happening. It has appeared that some people weren't affected by the issue and some where, and it appeared to depend on location. The entire reason for that confusion was the logarithmic scale for the bars. Yes, in fact, every single iPhone 4 is affected, but the effect is far less dramatic than previously thought. Roughly 20db attenuation. 5 bars went from -91dBm to -51dBm. So you could be at the high end of that, touch the spot, and still be in the five bar range. But if you were at the low end of 5 bars at -91dBm and touched the spot, it would still attenuate the same 20dBm but the bars would drop to 1 or 2 because of the ****ed up scale.

And while I can not verify the veracity of this next bug, I have read in a few different places (if I can remember where I'll post links) that there is a problem in the frequency switching code. It get's hit with the attenuation by touching the spot, the signal drops 20dBm, drops to a point where the phone goes on a fruitless quest to change frequency/towers but doesn't. It kinda gets stuck in limbo. And when it does that, it will eventually drop the call because it thinks it's lost the signal entirely even when there is a usable (albeit low strength) signal that's still there. This same behavior that's dropping calls is whats causing data transmission to completely halt when it drops suddenly, and then pick back up if the attenuation is removed.

If you combine that bug with the totally ****ed up bar scale, you get the exact situation we are seeing. Some people don't seem to have it (high signal, they have it, it just doesn't show in the bars because of the scale), those who DO seem to have the problem and jump from 5 bars to 1 bar (again, screwed up scale, it's the same 20dBm loss as those who are staying at 5 bars), and finally, dropped calls for some because it's fruitlessly hunting for a frequency change and gives up.

This turns out to be nowhere near as bad as it looked. Don't get me wrong, the antenna design is a gigantic bag of FAIL. You still get the 20dBm attenuation from touching the spot. But the effects of the attenuation where greatly exaggerated in the display and a second bug made it look like your signal was dying completely when you touched that spot.
 
LobsterDK said:
In case everyone hasn't read it yet, Anandtech has a review of the iPhone with a detailed signal strength analasys. This makes things so much clearer. The dBm to bar scale chart is about midway down the page.

http://www.anandtech.com/show/3794/the-iphone-4-review/2


The bar display "bug" was really screwing people up and distorting their perception on what was happening. It has appeared that some people weren't affected by the issue and some where, and it appeared to depend on location. The entire reason for that confusion was the logarithmic scale for the bars. Yes, in fact, every single iPhone 4 is affected, but the effect is far less dramatic than previously thought. Roughly 20db attenuation. 5 bars went from -91dBm to -51dBm. So you could be at the high end of that, touch the spot, and still be in the five bar range. But if you were at the low end of 5 bars at -91dBm and touched the spot, it would still attenuate the same 20dBm but the bars would drop to 1 or 2 because of the ****ed up scale.

And while I can not verify the veracity of this, I have read in a few different places (if I can remember where I'll post links) that there is a bug in the frequency switching code. It get's hit with the attenuation by touching the spot, the signal drops 20dBm, drops to a point where the phone goes on a fruitless quest to change frequency/towers but doesn't. It kinda gets stuck in limbo. And when it does that, it will eventually drop the call because it thinks it's lost the signal entirely even when there is a usable (albeit low strength) signal that's still there. This same behavior that's dropping calls is whats causing data transmission to completely halt when it drops suddenly, and then pick back up if the attenuation is removed.

If you combine that bug with the totally ****ed up bar scale, you get the exact situation we are seeing. Some people don't seem to have it (high signal, they have it, it just doesn't show in the bars because of the scale), those who DO seem to have the problem and jump from 5 bars to 1 bar (again, screwed up scale, it's the same 20dBm loss as those who are staying at 5 bars), and finally, dropped calls for some because it's fruitlessly hunting for a frequency change and gives up.

This turns out to be nowhere near as bad as it looked. Don't get me wrong, the antenna design is a gigantic bag of FAIL. You still get the 20dBm attenuation from touching the spot. But the effects of the attenuation where greatly exaggerated in the display and a second bug made it look like your signal was dying completely when you touched that spot.
Click to expand...

Edit: sorry I didn't read your entire post. I think you are def right, especially the second part. I can deal with a little attenuation, just not the total data loss. The second part is what I believe is fixable in software and apple should make a statement that it's coming instead of pull the crap that they have with the iPad wifi issue....I give them until tomorrow (genius appointment). If not, it's gonna be painful, but I can't justify keeping a flawed phone. No matter how much I want it....
 
Coukos34 said:
While this article is interesting, it does not explain how I can hold that point on the phone and then try to run the speed test app, and it will fail.....no data! Sorry but people are grasping for straws.....
Click to expand...

Actually, the article DOES explain why SOME users get no data when the phone is held or touched in just the wrong way.

And the article in question is already being discussed HEAVILY in this thread:

https://forums.macrumors.com/threads/956142/

Mark
 
Coukos34 said:
While this article is interesting, it does not explain how I can hold that point on the phone and then try to run the speed test app, and it will fail.....no data! Sorry but people are grasping for straws.....
Click to expand...

Agreed, I don't care what someone says regarding signal strength, if I can hold the phone in my hand and have data rate go to 0, and drop calls, who cares.
 
sorry. but it's not location problem. I tested few other cities already. it's totally hardware problem. period. who the hell said that is location problem? how can you explain that I had the same problem when I was in S.F, and Chicago, LA, New York recently? location? that's ********.
 
So what about the people with cases, like me, that are still experiencing drops and low speed or NO data at all?
 
archurban said:
sorry. but it's not location problem. I tested few other cities already. it's totally hardware problem. period. who the hell said that is location problem? how can you explain that I had the same problem when I was in S.F, and Chicago, LA, New York recently? location? that's ********.
Click to expand...

So because you have "extensively" tested this if FOUR cities across the nation, it is obviously not location related. Nice troubleshooting skills :cool:
 
archurban said:
sorry. but it's not location problem. I tested few other cities already. it's totally hardware problem. period. who the hell said that is location problem? how can you explain that I had the same problem when I was in S.F, and Chicago, LA, New York recently? location? that's ********.
Click to expand...
It is a problem with the hardware design of the iPhone 4. The issue appears or not depending upon your location and how strong the cell signal is.

Not sure what the argument is here.
 
archurban said:
sorry. but it's not location problem. I tested few other cities already. it's totally hardware problem. period. who the hell said that is location problem? how can you explain that I had the same problem when I was in S.F, and Chicago, LA, New York recently? location? that's ********.
Click to expand...

I believe it's a location issue. In my home in Los Angeles. When I hold the phone in left hand I do drop bars but never a call. It can make this happen every time at home. Today I went out to do a few things a few miles from my home. And I test to see if bars would drop and no dice. I held it for 5 min to see and the bars never went below 5.
 
It is 100% location specific. At my office, there is no way to hold the phone and make it even drop a bar (3-4 bars). At my house (5 bars) by barely touching the lower left I can, with every iPhone4 I have tried, get the signal to fall to nothing and drop a call.



ash =o)
 
No matter what the bars mean, and no matter what the actual signal ratio is or any of the other wonderful mathematical equations people are throwing around, the fact remains that a whole lot of people have their phones drop calls or lose connectivity simply by touching it "wrong".

This is a problem that needs to be fixed. I have the death grip problem, but not as bad as some. Again, it doesn't matter what the bars are showing or how accurate that is when people are losing connection completely or dropping calls.

I think most of the people (including all these "engineers" and Ars) that are trying to explain away the problem are the ones not greatly affected by it. That's great for you, and if you're not having your phone drop connection every time you touch it in the wrong place, I can see how you would think people are overreacting, but that doesn't solve the problem.
 
Vertigo50 said:
No matter what the bars mean, and no matter what the actual signal ratio is or any of the other wonderful mathematical equations people are throwing around, the fact remains that a whole lot of people have their phones drop calls or lose connectivity simply by touching it "wrong".

This is a problem that needs to be fixed.
Click to expand...

+1

Apple=****ers
 
Location (meaning, proximity to a cell site and the strength of that signal) is absolutely part of the equation.

The MAXIMUM drop in signal they were able to achieve (by cupping the iPhone 4 in the hands) was 24dBm. Then you have to consider:

• 5 bars of signal strength ranges from: -51dBm to -91dBm (-51dBm is the stronger signal)

So, if you have, say, -60dBm of signal and you cup the iPhone and attenuate the signal by the full 24dBm, the signal drops to -84dBm. That is STILL within a full 5 bars of signal.

Conversely:

• The range from the weakest side of 5 bars to no service: -91dBM to -114dBm (-113dBm is the lowest you can go without losing service)

That's a range of only 23dBm.

Therefore, if you just barely have 5 bars of signal (-91dBm) and you cup the iPhone and attenuate it by 24dBm, that drops you down to -115dBm and, bingo, you just lost service. This, despite the fact that your phone showed 5 bars of signal!

So, LOCATION is important because different locations will affect the signal strength.

Mark
 
blubyu said:
So because you have "extensively" tested this if FOUR cities across the nation, it is obviously not location related. Nice troubleshooting skills :cool:
Click to expand...

Sprint finds that many cities valid to claiming they have 4g coverage and can sell 4g phones to people across the country..
 
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