The Sound of Science - "Cell Phones"

Mar 22, 2019

J: I'm Jeremy Benson from NIU STEM Outreach and I'm in the studio with Kate Powers. This is the Sound of Science on WNIJ.

K: Hey Jeremy, I have a question from Steven for you today about our cell phones, and to be quite honest it is a question that I have as well!

J: There is a lot of cool technology in our hands these days - I'll see what I can do to answer.

NIU STEM Outreach

K: Steven, and I, want to know why our cell phones can pick up phone calls without interference from other cell phones? And even without interference from radios, WIFI and all sorts of other devices.

K: I know that all of these technologies use radio waves to transmit information, correct?

J: That's right. And let's start with the big differences: Different technologies are assigned different frequency ranges. FM radio is transmitted using waves with frequencies between 88 to 108 MHz.

K: Oh, so WNIJ is being transmitted here in DeKalb at 89.5 MHz? And when you say frequency of the radio wave you mean how fast the wave is oscillating, right?

J: Exactly. Different antennas are tuned to pick up different frequencies. Cell phones communicate in two different bands: 1850 to 1990 MHz or 824 to 895 MHz. When you make a call your cell phone connects with a local tower and is assigned a specific band within those ranges. The tower makes sure that no other calls are being transmitted on the frequency that your call is using.

K: But there are so many cell phones, and Bluetooth devices and WIFI routers. How are there enough different frequencies for all of them?

J: Well, there are obviously millions of devices out there transmitting info via radio waves. But they aren't all transmitting right here and right now. The same frequency can be used by a different cell phone across town, as long as it is using a different tower to access that frequency. But there can be interference! Interference is what creates dropped calls and bad service. That is especially true if you are on your phone as you move from one cell tower to another.

K: I get the feeling this is a very complicated subject Jeremy, but thanks for beginning to explain it to me. Keep your questions coming to stemoutreach@niu.edu. This is the Sound of Science on WNIJ.

J: Where you learn something new every day.