Showing posts with label Blackberry. Show all posts
Showing posts with label Blackberry. Show all posts

Tuesday, January 26, 2010

How To Put Your iPhone Into Field Test Mode & Compare Signal Strength Bars To Actual Signal Levels

In a previous post I showed how to do Decibel (dB) calculations when both the input power and output power are known for a transmission system. We learned that a 50% decrease between input and output power results in a power loss of -3 dB with the negative sign indicating the loss in power.

These calculations work great if you know both the input and output power but - what if you don't know the input power? And, because dB calculations are made based on an output power to input power ratio, they really don't tell you much when it comes to things like actual signal strength. What's the solution? Something called a dBm calculation. dBm calculations are done in basically the same way we do dB calculations, the only real difference being we replace the input power value in the equation with a 1 mW constant:

Psignal in dBm = 10 x log10(Psignal in Watts/1mW)

Where Psignal in Watts is the signal strength measured in Watts. This equation can be simplified using some basic math since 1mW is now a constant, yielding:

Psignal in dBm = 10 x (log10Psignal in Watts) + 30

Pretty simple, the dBm level of a signal that has been measure in Watts is just ten times the base-10 log of the measured signal plus 30. It's actually so simple it's much more common to measure and indicate communications signals in dBm. In fact, you can take some measurements yourself if you happen to own an iPhone. Let's learn how.

The iPhone has the ability to go into something called Field Test mode. Once in this mode you can look at signal strength in both signal bars (what we are all used to seeing) and also in dBm. To put an iPhone into Field Test mode just punch in the following number on the phone keypad, including the "star" and "pound sign" keys:

*3001#12345#*

After you punch these numbers and symbols in, hit the Call button on the keypad and you'll end up with your iPhone screen looking like this:


Lots of interesting stuff here but - for now - let's ignore everything but the upper left hand corner of the screen. Take a look at where you usually see the signal bars and you'll see a negative number - this is the actual cell signal strength your phone is receiving in dBm referenced to 1 mW. In the above screen shot I'm measuring -113 dBm. Touch that signal strength number once and it toggles to the familiar signal strength bars:


Touch it again and it flips back to the strength number. You get the idea. What constitutes a good signal? Here's some rough signal strength guidelines:

Full Signal:-70 or lower
Optimal Signal:-70 to -75
Fair Signal:-75 to -85

Poor Signal: -85 or higher

Remember as a negative number increases in its numeric value it is actually decreasing with reference to zero. This means a -70 dBm signal is stronger than a -85 dBm signal.

This is interesting to experiment with - check your signal strength in different locations see and how it correlates to the numbers of bars you are getting. Does it match up? Not always based on my experience!

To exit out of Field Test mode on the iPhone just hit the Home button.

Have a Blackberry? (I don't so proceed with this one at your own risk) I've been told you can do something similar using the secret code Alt-NMLL to convert your bars to numbers. To convert back to signal strength bars just enter the same secret code again.

Have a phone other than an iPhone or Blackberry? Most phones will allow you to go into some sort of field mode to see actually signal strength numbers. Check your manual or do some searching on the web to find out how.


7/6/10 Update: This function appears to be disabled after completing the iOS 4 Software Update

Tuesday, December 9, 2008

Some Interesting Wireless Device Development Platforms

Last month the Rutberg & Co. Wireless Industry Newsletter asked the question Will 2009 be the year of the mobile app? I've been watching the different mobile development platforms fairly closely because these applications offer some great teaching and learning potential in our classrooms and some excellent business opportunities for our entrepreneurial students. The Rutberg newsletter lists four different device platforms:

Most developers consider the iPhone SDK king right now - Apple currently provides the richest development environment along with marketing and the App store where developers can sell their applications.

Googles entry involves the Open Handset Alliance, a group of more than 30 technology and mobile companies that developed Android.

Ovi was launched in late summer 2007 by Nokia as a "personal dashboard" for Nokia smartphones.
The company has launched the BlackBerry Developer Zone with resources and information for developers.

Each site offers the equivalent of an SDK along with other developer tools, white papers, forums, videos, etc. The Rutberg newsletter says it well - Apple pioneered the offerings of a compelling data experience to customers, a useful development environment for developers, and a meaningful business model for constituents throughout the ecosystem. Android is furthering the industry shifts through greater levels of openness and broader levels of industry involvement. Ovi and Blackberry are right there in the mix too.

If you currently teach computer programming you should take a close look at each of these development platforms.