This is not exactly new, but it is a handy tip for new iPhone users or simply to show off to your buddies how “geeky” you are. :)
Go to your dial pad, enter the following and followed by tapping on Call:
*3001#12345#*Editor's note: learn more by reading our ebook on starting your own iPhone repair & unlock business
This will launch Field Test Mode as shown below.
Take note of the number on the top left corner. That indicates your iPhone’s signal strength in dB-microvolts per metre (dBµV/m) or in decibels above a reference level of one milliwatt (dBm).
The lower the number, the better your signal is. e.g. -51 is full signal, -105 is no signal. For my case above: -74 is a pretty good signal.
You can toggle between the number and signal bars by tapping on the top left corner of your screen.
This is relatively useful to test whether the iPhone casing you’re using is actually reducing the efficiency of your iPhone’s antenna. For most parts, your iPhone casing shouldn’t interfere with the operation of its antenna.
Now for more technical stuff, when testing it in a 3G environment, it is possible to determine the frequency being used by selecting: UMTS Cell environment, then select UMTS RR info. The screen displayed will list the Uplink and downlink Frequency in code form.
Uplink frequency on the 850 MHz cellular band will list an Uplink Frequency code between 4132 and 4233 and a Downlink Frequency code between 4357 and 4458. If you are operating on the 1900 MHz spectrum the Uplink Frequency code will be between 9262 and 9538 with the Downlink Frequency code being between 9662 and 9938.
Kinda neat, huh? How’s your iPhone’s signal strength? Do share…