GSM Problem after flashing ROM

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http://forum.xda-developers.com – Dear friends, I have a Samsung Galaxy Note. I tried flashing several custom ROMs. Then I figured out that my GSM modem loses signal every now and then and I have to restart the phone every couple of minutes. (Going to flight mode and returning back also works). I thought it relates to Custom ROM, so I get back to the stock ROM, but didn't solve the problem. I tried flashing different modems using Odin, but all of them are losing signal... So currently I can't use my phone :( I live in Iran and tried the following modems: XXLA1 XXLA3 XXLA4 (My friend's Galaxy Note official ROM uses (HowTos)