T-Mobile Nokia 5G21 Interesting Discovery

[Murphy625]

If you have a Nokia 5G21 router from T-Mobile, you might be interested to find that the square white wall wart transformer that is uses to provide 12vdc power is very noisy.. and if placed too close to the unit, it will tax you almost 5 to 7db in SNR.

I discovered this accidentally while diagnosing speed/signal quality issues. Decided to break out the toughbook laptop and take my modem for a ride to the tower.. I quickly discovered that the modem didn't like the modified signwave 12v to 120vac inverter I was using.. It would power up, connect to the tower with 4 bars, but I couldn't get internet because the SNR was 0.

So came home, checked the wall wart transformer for voltage and found it right at 12.4 volts.. Wohoo! Easy solution, just plug it into the aux power outlet in my vehicle.. So drove back to tower, shut off vehicle so the modem wouldn't see the 14.4 volts from the alternator, and plugged the modem in directly to the battery.. Nice fast internet.

Came home, put it back on AC power and noticed my SNR was bouncing between 4db and 10db... sometimes going to 12.. So on a whim, I decided to get a 12 volt battery and plug it into that.. WOW.. Instant 5 to 7 db gain on the SNR Ratio.. Now it bounces between 18db and 12 db.

My average download speeds went from 20 and 25 MB/s to 40 to 50 MB/s, and my upload doubled from 3.5 to 7..

Plugged the modem back into the white boxy wall wart, and my SNR went back down to the old levels and downloads went back down to 25 range..

Wohoo! I don't know if that was my problem, but it sure seems to have made a significant difference.. another 24 to 48 hours will tell the whole story..

I know one thing from experience, my HF Ham Radio does not like high frequency power supplies.. When I plug my laptop in next to the radio, I can actually hear the transformer.. it makes a buzzing sound in the Ham radio frequency bands.

[Murphy625]

UPDATE:
Still playing with it.. Finding that the increase in SNR might be because I'm testing at night an its an hour later..

Not clear yet.

[Didneywhorl]

Very interesting discovery! Thanks for posting it here, love it!