GSM Field Test

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What Is GSM?

GSM stands for Global System for Mobile communications (originally Groupe Spécial Mobile). It’s the standard developed by the European Telecommunications Standards Institute (ETSI) to describe protocols for digital cellular networks used by mobile phones. As of 2014 it has become the default global standard for mobile communications.

What Is A GSM Field Test?

A GSM field test uses a cell phone to measure cellular signal strength in dBm (Decibel-milliwatts). One dBm is only one 1,000th of a Watt (power). Because cell phones operate at very low dBm and decibels can be measured at very low values, GSM network signal strength is measured in dBm.

Why Read dBm Instead of Bars On Phone?

The short answer is that bars on your cell phone are not precise and really aren’t designed to indicate signal strength any way even though that’s what most people think. If you are considering purchasing a product other than a cell phone that transmits data over a cellular network from a fixed location, you will first want to measure the signal strength in dBm where it will be located to make sure you have enough signal. A GSM field test does that.

To get a good grasp on why it's sometimes better to read dBm, you first need to understand what bars really represent. Bars on a cell phone give users a quick view of the approximate level of reception they are getting. Reception is how good your connection is and how well you hear your caller. Originating from the old Five-by-Five protocol, up to 5 bars show levels of reception.

Calculations done by your cell phone determine the number of bars shown. They are specifically designed to show levels of reception and are based on different factors, not just dBm readings. They’re not intended to represent any specific amount of dBM.

Bars indicate ‘no’, ‘bad’, and ‘good’ reception. How many times have you had a dropped call? Usually there are no bars, which mean ‘no’ reception. How many times have you told or been told “you’re breaking up”. That usually happens when there are only one or two bars, which is considered ‘bad’ reception. With three or more bars you usually have ‘good’ reception. Those are generally accepted meanings that experienced cell phone users live by.

It’s also important to know that different cell phones can calculate reception levels differently. That explains why your phone can show 3 bars while your friend’s phone shows 4 bars even though you are in the same spot. That’s also one of the reasons why a GSM field test might show low dBm while your cell phone is showing a lot of bars or vice versa. Bottom line, bars don’t give you a precise measurement of signal strength.

A GSM field test will give you a precise measurement of signal strength. Your cell phone operates off of a mobile phone signal and readily senses the signal in dBM. So to get a precise measurement of cellular signal strength you need to do a GSM field test so you can read it in dBm.

GSM Field Test Instructions

Position the cell phone carefully. Here are two important tips on that:

TIP-1: If you are checking cellular signal strength in anticipation of purchasing specialized equipment that transmits data via cellular networks, be sure to put the phone exactly where the antenna will be located. If the antenna is built into the device, then it’s important that you put the phone exactly where the device will be mounted. To be on the safe side, before making the purchase, we recommend finding out the manufacturer’s signal requirements in dBm and comparing them to your test findings.

TIP-2: For most accurate reading, set cell phone on a surface other than your hands and press refresh again. Sometimes holding the cell phone in your hands can affect the reading a bit.

Run the apps. To ensure accurate readings, carefully follow these instructions for Android phones and iPhones.

Android Phones:
First download a GSM field test app. Below are three that were available at Google Play at the time of this writing. They’re in order of our preference:

  1. Network Signal Strength
  2. GSM Field Test
  3. Network Signal Info
The following example is with the Network Signal Strength app. After loading and setting up per app instructions, start reading dBm at different locations. Each time you move to a new location press the refresh button.

With an Apple iPhone, you can get these readings without downloading an app. Just follow these steps:

  1. Dial *3001#12345#* (Your iPhone will then launch Field Test).
  2. Press the first arrow as shown in the diagram below.
  3. On next screen look for dBm.
  4. To terminate session, press and hold the Home button.

The Future

If you find a better app for performing GSM field tests or have some other thoughts on this procedure, we would love to hear about it. Please use Contact Us to get in touch.

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