GSM Monitor Station

Details and FAQ on the UltraATA Chicago GSM Monitoring Station

I am currently running a live stream capturing the final days of the T-Mobile US GSM network in Chicagoland. I am located out of McHenry County, and my goal is to capture the GSM shutdown in my area.

What SDR am I using?

I am using a Nooelec NESDR with an E4000 tuner chipset. Unlike most RTL-SDRs, the E4000 tuner allows me to tune up to ~2180 MHz, and capture T-Mobile's 1900 MHz GSM signal.

How long will the stream last?

This stream will run continuously 24/7 until the GSM network is no longer being broadcasted in my area. GSM is expected to shut down on August 3rd, 2026 at approximately 00:00 - 05:00.

What are you seeing?

You are viewing 3 of T-Mobile's GSM channels as a waterfall view. The top graph shows physical RF signal strength in a 2.4 MHz window. The 3 bumps are individual 2G GSM channels, and the wide signal next to it is T-Mobile LTE B2.

The bottom view is a waterfall, showing the signal over a short amount of time. Strong signals are indicated in red/orange, weak signals are indicated in yellow/light blue, and the noise floor is dark blue.

What are you hearing?

You are listing to one T-Mobile GSM channel demodulated with AM. With this configuration, you are able to audibly hear traffic on the GSM network, and you will be able to tell when the signal drops to static.

What is that rumble noise?

Due to tower placement, my nearest T-Mobile site is over 3 miles away! This introduces interference for two reasons: multipath interference and overlapping cells. In GSM, each cell is supposed to utilize its own dedicated ARFCN. Unfortunately, T-Mobile only has 6 ARFCNs available, and there are more than 6 towers in my area.

Additionally, due to my distance from the nearest site and the obstacles in between, there is a phenomenon known as multipath interference that can be observed. Multipath interference occurs when a signal (usually narrowband) reflects off of buildings and other surfaces, and hits the receiving antenna later than the original signal. In my stream, this is observable as a low rumbling noise that fades in and out depending on the environment. Multipath interference is particularly an issue with TDMA-based networks (such as GSM)