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I want to force my cellular modem to transmit at maximum power so that I can see if that is the cause of microSD card crashes that I have been experiencing in an embedded application.

My modem is a ublox U-260, and the AT command manual for it is here.

I know that the modem "throttles" its transmission power based on the intensity of the received signal (from the cell tower) so you can force the modem to transmit at maximum intensity by putting it somewhere with poor cell reception.

I have been unable to get my cell reception to be bad, however, as there are a number of cell phone towers nearby.

So, seems to me there are two options:

  1. Physical solution: Attenuate cellular signals arriving from cell tower to modem via some type of physical solution

  2. Software solution: Force the modem to transmit at maximum power levels regardless of strength of received signal by configuring it to do so via AT command (software solution)

So, anyone out there know how to implement one of these solutions? I have tried building a faraday cage around the modem by lining the enclosure that it's in with aluminum foil and attaching an alligator clip to mains ground.

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A microwave oven acts as an easily accessible and highly effective Faraday cage at RF wavelengths. Place the phone in one. Perhaps unplug the oven to avoid accidents.

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    \$\begingroup\$ This might work in practice, but a microwave oven is actually not a (broadband) faraday cage, as there's no electrical contact sealing the door . Instead, the door mates via a frequency-specific structure which won't be right for all mobile bands. \$\endgroup\$
    – Chris Stratton
    May 2, 2018 at 13:59
  • \$\begingroup\$ Microwave ovens do operate in the same frequency range as cell phones, though. \$\endgroup\$
    – Hearth
    May 2, 2018 at 14:32
  • \$\begingroup\$ @Felthry Not really. Microwave ovens are ~2.4 GHz; cellular bands are 800/850/900 MHz, and 1.8/1.9 GHz. The latter two are closer, but not that close. \$\endgroup\$
    – user39382
    May 3, 2018 at 17:00
  • \$\begingroup\$ A microwave oven will only block the ovens operating frequency . If you put a cell phone in a microwave ( that is not operating at the time obviously) it will still receive cell signals and will ring inside the oven same with cordless phones as well. The door seal acts like a very sharp notch filter at 2450 MHz. Everything above and below will pass. I have already experimented with that. \$\endgroup\$
    – Old_Fossil
    Jul 8, 2018 at 6:54
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Software solution

I can assure you that this absolutely will not be possible. There are strong regulatory and type approval requirements on transmit power, and the user is no way allowed to change it arbitrary to his/her own target.

Outside of custom debug test firmware where someone modifies the source code and compiles themselves, changing the transmit power from what the radio controlling software calculates to be appropriate is impossible.

I worked over a decade at Ericsson developing and maintaining AT commands, and I am sure that none of our phones ever had debug AT commands for changing anything significant related to radio (and none of those debug commands would ever be part of a released product).

I once met a colleague that had a phone with modified test firmware that allowed him to change the call priority on regular phone calls (as far as I remember 1/high is used for emergency calls, 2/medium is used for normal calls and there is also a third low priority), but again outside of custom test firmware you modify and compile yourself, there is no way to do this on normal phones.

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