Can I trust a cell phone to report an accurate and precise signal strength?

My company builds and deploys an IoT device that currently uses a 3G modem. There are a number of these devices in the field and I'd like to improve our process when choosing sites.

Most phones support a mode to report the signal strength in dBm. So I can take an iPhone that uses the same network, disable LTE, and I'll get a number. It's not clear to me however if this number is meaningful, accurate, or precise.

Should I purchase a dedicated meter? If so what specs should I pay careful attention to? Any advice on a good measurement procedure once I have selected a number-giving device?

Thanks for reading.

Yes, you can trust a 3G cell phone (or modem) for signal strength measurements, with a +/-1dB accuracy. Have to be inside of the dynamic range of the receiver, and about 3dB above the sensitivity level.

yeah but i would not try to HOLD the cell phone in my hand! The antennas are built into where you hold them.

This is interesting! How do you access that measurement mode on the Iphone?

1. Different phones report different signal strength on the same network at any given place and time.

2. Signal strength depends on the relative orientation of the phone and I do not know how to get the reading in dBm.

3. Any device you decide to buy should be tested with a reliable desktop meter IF you wish the readings be reliable - precision is more important than accuracy.



How do you get the cell phone to display the signal strength in dBm? Is there a specific app for that?

I am bit worried about installing many apps because ALL want to access the contact list and photos!

Even if the measurement displayed by the phone was precise, I think it would only be useful for relative measurements (like for observing antenna sensitivity profiles, path losses, etc), not for deriving accurate field strengths at a given location. Consider that these devices are working with modulated signals, so a simple "dBm" measurement isn't even straightforward.

What exactly do you want to derive from these measurements?

Take care that the SS indicated is with the antenna, not the field strenght.
If you have to trace the field strenght, you need a calibrated antenna and a calibrated receiver.
On the legal point: how can you show the results, when you do not know antenna gain, direction of reception, disturbs from the surrounding surfaces(reflections) and all the chain is not certificated and calibrated ?
If you do it for youself it could be interesting, but if you are working for a company this is not the way.

i am not sure what you mean when you say "a 3G Modem". are you ssking signal strength of an LTE cell phone signal, or are you instead talking about in-building WLan 2.45 GHz signal strehth? THe later has a hundred ways to test it easily and cheaply.

For the ones who are wondering how to see signal level in dbm in an Android Phone you can go to setting and select the status. Under there you can see signal level of gsm network.