How to Use Phone Field Test Mode

Here at OptConnect, one of our goals is to provide you with enough resources to have better success in all your installations. Did you know that cell phones are a highly versatile tool that can be used to help you identify cellular connections at various locations? Some phones have built-in tools to gather this information while others may utilize free or paid apps.

These signal checks at any given location are what we typically call a “site survey”. These site surveys can be highly useful in current and future deployments. All phones are different so the steps may vary depending on your model.

Industry Standards for Measuring Cell Signal Strength

The standard industry measurement for cellular signal strength is decibel milliwatts, or dBm. You can find this measurement on your iPhone only when you’re in field test mode. So how do you enter field test mode?

Accessing Field Test Mode

There are different ways to enter field test mode, depending on which version of iOS you’re using. Keep in mind that the steps may differ slightly due to the model of iPhone and cellular carrier.

Using Field Test Mode on iOS 11 and Later Versions

Follow these steps:

  • Turn off the phone’s WiFi connection

  • Open the Phone app

  • On the keypad, dial *3001#12345#*

  • Press call

You should now see the field test mode menu. To view your phone’s signal strength in dBms for the nearest cellular tower:

  • Select LTE if given the option. On some iPhones, you may be taken directly to the next step.

  • Select Serving Cell Meas.

  • Select rsrp0.

Selecting rsrp0 tells you the strength of the signal you’re receiving from the nearest cell tower. If you choose rsrp1, you’re getting a reading from a further tower.

If you are using iOS 14 and later, then the hidden field test mode interface has been redesigned. To access field test mode on iOS 14, you follow the same steps listed above. You will then be taken to a dashboard where you can see your LTE dBm reading and other metric data.

Using Field Test Mode on Older Versions of iOS

Follow the instructions above if you’re using an older version of iOS through AT&T or T-Mobile or an iPhone with an Intel chipset.

If you’re using an older version of iOS through Sprint or Verizon, or an iPhone with a Qualcomm chipset, you need to first turn off LTE:

  • Select Settings.

  • Select Cellular.

  • Select Cellular Data Options.

  • Turn Enable LTE to the off position.

To view your phone’s signal strength in dBms for the nearest cellular tower:

  • Select 1x EV-DO.

  • Scroll to Rx AGCO.

Measuring Signal Strength

Typically, the strongest signal you can obtain on your iPhone is -50 dBm. If you have anything less than -100 dBm, you likely won’t have any service.

Here’s a quick guide to signal strength:

  • Excellent: -64 dBm to -50 dBm

  • Good: -65 dBm to -84 dBm

  • Poor: -85 dBm to -100 dBm

  • Very weak or no signal: -110 dBm

For full functionality, aim for a signal strength between -50 dBm and -80 dBm. This should provide a reliable connection for calls and data transfer. If your cell strength falls below this range, you might want to consider a cell signal booster in your home to ensure more reliability.

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