Electronics > RF, Microwave, Ham Radio

Suggestions on circuit design for LTE-M

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diminatto:

--- Quote from: RadioNerd on January 19, 2025, 09:16:56 am ---Based on your description I would first check all components in the RF signal path.
Is everything electrically connected? all solder joints OK? All components oriented the right way? I would especially check the SMD coax receptacles. With these IPEX (or whatever standard it is) receptacles it can somtimes happen to mount them rotated by 180 degrees by mistake which will short the RF line...

--- End quote ---

There´s only one 0 ohm resistor in the path, already checked with a multimeter and everything is connected from the modem to the coax on the antenna. I soldered them incorrectly the first time lol, but they have a little indentation on them pointing the grounded side and now they are ok.

I have three samples with the same problem, i already reflowed them to discard bad soldering.

diminatto:

--- Quote from: diminatto on January 19, 2025, 03:00:16 pm ---
--- Quote from: Kean on January 19, 2025, 06:47:58 am ---Have you tried building and testing a second sample?
There is the possibility of an assembly issue, and you might want to rule that out.
You could also try extending the ground plane by scraping away some of the solder mask around the edges and soldering on some thin copper sheet/tape.

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I made three samples, they all have the same problem, gonna try adding some more ground.

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Tryed adding some more ground, still have the same problem. Didn´t have copper sheet or tape so i welded to a PCB.

diminatto:
A little bit more information i collected, if i try to connect to the network it answers me with reject_cause 15 "No Suitable Cells in Tracking Area". If i do a AT+COPS=? to list all the operators, it takes some time to give a response, but the command brings two, one of wich is the operator from the SIM card.

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