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Apple's upcoming iOS 14 update introduces multiple design changes, including a new look for the hidden Field Test Mode feature on the iPhone.

As noted on the MacRumors forums, Apple has overhauled Field Test Mode to provide more useful information at a glance.

ios14fieldtestmode.jpg
Field Test Mode in iOS 14​

There's now a Home section with LTE Cell Serving Info, along with a menu section that has other details like device info and breakdowns of LTE, UMTS, and GSM functionality.

Much of the info available in iOS 13 and iOS 14 is the same when it comes to Field Test Mode, so the change is primarily related to design and making it easier to navigate through the hidden app.

Field Test Mode is designed to allow iPhone users to access in-depth information about cellular signal and cellular connection. Field Test Mode is designed for engineers and cellular operators and most people will not need to use it on a regular basis.

ios14fieldtest.jpg
Field Test Mode in iOS 14​

You can access Field Test Mode on an iPhone by opening up the Phone app, inputting *3001#12345#* and pressing the phone button. It won't make a call, but will instead open the Field Test app.

Field Test Mode was formerly useful because it could turn the cellular signal bars into a numerical measurement, but that is not something that works on modern iPhones with recent versions of iOS.

ios13fieldtest.jpg
Field Test Mode in iOS 13​

It can still sometimes be useful to see cellular signal represented as a number, and that's still possible on iOS 13 and 14. After entering the Field Test app, tap on LTE (from the main menu on iOS 13 or the menu list on iOS 14) then tap on "Serving Cell Meas."

The measurements that read "rsrp0" and "rspr1" are your cellular signal strength in decibel-milliwatts. These numbers are always negative, and a lower negative number is better than a higher negative number and represents a stronger connection. Numbers range from about -50 to -130. Closer to -50 is a strong signal strength, and when you get to around -100, that's a poor connection that's spotty with slow data speeds if a connection can be made at all.

Article Link: iOS 14 Includes Redesigned Field Test Mode
 
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apparatchik

macrumors 6502
Mar 6, 2008
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-130 is a lower number than -50, and is more negative, though. Rather than “a lower negative number is better,” it’s more accurate to say “a less negative number is better.”

I was about to point this, definitely confuse wording, -130 is lower than -50, “higher negative” is not the best way to put it, -50 is both negative and higher than -130, so, it is a higher negative number than -130 in a sense. I think a number is either negative or is not, talking about degrees of negativeness instead of the number being higher or lower period is imprecise. So, higher numbers are better in terms of receiption, period. No need to say more than that them being negative is expected.
 
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ApfelKuchen

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Aug 28, 2012
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We need a manual for this field test so people can understand exactly what is what!
Yep, because this is a clear case of "a little knowledge is a dangerous thing." It's the kind of info one might see in a professional telecommunications test instrument. It's not a go/no-go test, it's quantitative measurement. Unless you know what every measurement means and how various measurements interrelate, it's nearly useless. But an end-user can latch onto one or two measurements out of the bunch and decide they have a problem.

Radio signal strength/signal quality measurements are particularly tricky, as strength and quality are affected by even small changes in the local receiving environment - moving as little as a few inches or slightly changing the angle of the receiving antenna can make a huge difference.

Consider the comments about whether -130 should be considered "lower" or "less negative." In the case of signal strength, -50 is a stronger signal (better) than -130. However, if we were talking about a noise measurement, -130 would be better than -50. Still, this doesn't tell us whether -130 is good enough.
 
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Ion-X

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Oct 23, 2017
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I was about to point this, definitely confuse wording, -130 is lower than -50, “higher negative” is not the best way to put it, -50 is both negative and higher than -130, so, it is a higher negative number than -130 in a sense. I think a number is either negative or is not, talking about degrees of negativeness instead of the number being higher or lower period is imprecise. So, higher numbers are better in terms of receiption, period. No need to say more than that them being negative is expected.

As a math teacher, explaining that a negative number with a higher absolute value is lower than a number with a lower absolute value is one of the most confusing things I do! Our language almost isn’t set up to describe these things clearly.

Technically, what you suggest is accurate, but when looking at negative numbers most people just consider the absolute value and would say that -130 is “bigger” than -50. So using an analogy of a number line and saying that numbers closer to 0 (or in this case -50) are better is probably the most helpful strategy. The most important thing though is to not use inaccurate language like lower is better when in fact higher is better.
 
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compwiz1202

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May 20, 2010
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-130 is a lower number than -50, and is more negative, though. Rather than “a lower negative number is better,” it’s more accurate to say “a less negative number is better.”
First thing I noticed. They could also say numbers of less magnitude represent stronger signals.
 
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littlepud

macrumors 6502
Sep 16, 2012
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We need a manual for this field test so people can understand exactly what is what!
I find it strange that it doesn't look like iOS at all.

A manual and a nice interface are both completely unnecessary. The labels and meaning for each value are all in the UMTS/HSPA/LTE specifications defined by 3GPP, the standardization body that writes the cellular network specs. Anyone who truly needs to work with the Field Test Mode (i.e. an RF engineer working for a mobile carrier or a cell-site / base-station manufacturer) would already know what to do with all of the output. This is not a feature meant for end-users (like most on the forum here) and is not really useful beyond being a technological curiosity.
 
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twolf2919

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Aug 26, 2014
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Yep, because this is a clear case of "a little knowledge is a dangerous thing."...

Maybe, but it can also be extremely useful - even if you don't know what one or two numbers are about. Case in point:me! We moved to a new house whee my T-Mobile cellular connection showed "No service". But by looking at the field test screens, I saw that there actually was a signal - it's just that the iPhone interprets it so weak as to constitute "No service". Knowing this, I was able to get cellular service by installing an antenna on the roof - again using the field test mode to point it in the best direction - and an indoor amplifier (and indoor antenna). Now I have service. And the only measures in field test mode I used were rsrp0 and another one that measured quality rather than strength but whose name I already forgot again :)
 
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apparatchik

macrumors 6502
Mar 6, 2008
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As a math teacher, explaining that a negative number with a higher absolute value is lower than a number with a lower absolute value is one of the most confusing things I do! Our language almost isn’t set up to describe these things clearly.

Technically, what you suggest is accurate, but when looking at negative numbers most people just consider the absolute value and would say that -130 is “bigger” than -50. So using an analogy of a number line and saying that numbers closer to 0 (or in this case -50) are better is probably the most helpful strategy. The most important thing though is to not use inaccurate language like lower is better when in fact higher is better.

Yeah, "values closer to 0 represent better reception" sounds like the clearest way to describe it, Ive never heard 120 as a "higher positiveness/more positive" number than 50, the whole positiveness/negativeness concept, both mathematically and as a figurative resource seems wrong to me.

The fact that reception measurements in this context are negative is secondary and irrelevant to the fact that higher numbers represent better reception, as long as you grasp the basic concept that -50 is higher than -55, there's no need to say more than that.
 
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melgross

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Jan 23, 2004
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Im getting around -105 to -110 here in my dining room, as it changes, but have no problem with a signal. Signal loss gets tricky below -120.
 
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ApfelKuchen

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Aug 28, 2012
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Between the coasts
Maybe, but it can also be extremely useful - even if you don't know what one or two numbers are about. Case in point:me! We moved to a new house whee my T-Mobile cellular connection showed "No service". But by looking at the field test screens, I saw that there actually was a signal - it's just that the iPhone interprets it so weak as to constitute "No service". Knowing this, I was able to get cellular service by installing an antenna on the roof - again using the field test mode to point it in the best direction - and an indoor amplifier (and indoor antenna). Now I have service. And the only measures in field test mode I used were rsrp0 and another one that measured quality rather than strength but whose name I already forgot again :)
Yes, if you're considering a cellular signal booster, you can put this to good use. I found a very good article about using Field Test Mode at a site that's in the business of selling boosters (although the article seems to have last been updated around iOS 9 - following their instructions on how to replace the cellular bars in the Status bar with a Db reading did not deliver that result in iOS 13.6 on an iPhone with Face ID). But once you get past that fairly straightforward application, you need to know a whole lot about cellular technology and the specifics of your provider's network.
 
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Stridr69

macrumors regular
May 8, 2012
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ja9G0HvnRH-Ds9YaKcV1TA.jpg
ja9G0HvnRH-Ds9YaKcV1TA.jpg

Too bad that iOS doesn't allow the use of apps like this one. However this can be used as a reference.
For example -101 dBs = RSPO on iOS. The lower the number, the better the signal.
LTE+=CA status IS in use. This particular app dosen't show total Mhz bandwidth in use, unfortunately(like another app that I use shows 3XCA:20x5x5MHZ for a total of 30 MHz
The number 66 on the upper right is the frequency band band in use. Don't see it on the examples given here in this thread. S/B freq_band_ind 66
Fc=Actual frequency used, in this case 2145 Mhz(2.145 Ghz)

Reference only folks, but fun to use...
 
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