Can band 12 b and c blocks interfere with band 12 a block?


    I have a complicated and specific question.

    Is it possible for AT&T band 12 B and C blocks to interfere with T-Mobile's band 12 A block?

    This is the scenario behind the question: One of my favorite vacation places is the Pennsylvania Grand Canyon. My retired aunt and uncle have a cabin near a small town called Oregon Hill that I often visit. There's a big T-Mobile tower approx 10 miles North-Northeast in a small mountain top town called Antrim. I get about one bar at their cabin from this Tower. AT&T only has 3g 850mhz service at my aunt and uncle's Cabin. My father is a member of another cabin, and the same Tower is approx 16 miles northeast from this cabin. This cabin is about 200 yards from the top of the mountain, and if you walk to the top, other than leaves from the trees blocking you, you are directly within line of sight of that Tower. At the top of this hill AT&T has 1-2 bars of LTE coming from a tower who-knows-where. I am on a T-Mobile Galaxy S7, and when I go into my service mode info page through the dialer app my phone shows that it detects the T-Mobile tower with strength around -100 dbm.  The tower that my phone dectects has the same physical cell identity as the tower in Antrim, but it cannot connect to it. After about 30 seconds of saying no service and showing in the service mode app that it is detecting the tower at Antrim, the physical cell identity changes for a few seconds, displaying the physical cell ID of the AT&T tower, then everything goes to emergency calls only on the AT&T tower. Even if I go to the network operators section in settings and do a network search, T-Mobile comes up, but when I attempt to select it says unable to connect to T-Mobile network. (This all happens at the top of the MTN near the 2nd cabin)

    The more complicated question is why am I able to connect to the Tower in Antrim at my aunt and uncle's cabin, without a direct line of sight to it, and at the cabin that my dad is a member of I cannot connect to the tower but we do have a direct line of sight to it.

    The same thing happened when I used a Moto x pure, and iPhone SE in the same locations.


    I apologize again for writing something so long, but hopefully I provided as much information as possible.

      All replies

      • stevetjr

        well may not be able to answer your question entirely but can clarify some of what you pointed out.  First thing is Band 12 is strictly A block 700.  AT&T saw to this because they didn't want the "regional carriers" (before TMO got their Band 12) to be able to roam on their network so they came up with some bogus studies that the A block was harder to filter yada yada yada, so they got their 700 holdings banded desperately into Band 17.  However after TMO and some other carriers got the FCC to look at it and the FCC started probing AT&T saw the writing on the wall and backed off and made their Band 17 towers capable of interoperatbility with Band 12 but they still maintain their Band 17. 


        As for why you can pick up the tower when non line of site the only thing I think it could be is which way the antenna's are aimed or it could be that the AT&T tower is fooling your phone into thinking it can connect so it ignores the TMO tower.  One thing about Band 12 is that it is a secondary channel and the phone will always try to connect to TMO's primary Band 4 (Band 2 in a small amount of markets).  One thing you could try is turn of roaming while your there and see if that gets it to look for native TMO towers.

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          • cowbob24

            Okay. The antenna aiming makes sense, and next time I go up there i will have to try disabling roaming. Hopefully that will solve the issue! I've fiddled with the band selection settings on my Galaxy when I was near the tower and I'm pretty sure it's a band 12 only tower, but I'm not positive.

            So when a phone is searching for LTE on band 12 it will search band 17, as as well?

              • dragon1562

                I would also guess that it has something to do with how the antennas are aimed. Also your phone shouldn't try to connect to other carriers networks since the software has been modified by T-mobile to work a specific way.

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                • tmo_mike_c

                  Hey there! It looks like you got some really good advice and suggestions from our fellow members. I'd just like to add that I don't imagine AT&T's band would interfere with the T-Mobile band. Your connection would depend on the phones capabilities and your distance from that tower. With the "unable to connect" error, it could mean that tower could be going through some upgrades and may not allow access for some time. I'm curious if there are any other folks there with T-Mobile that are able to connect to that tower. If it's just happening here, we may need to get engineers involved with a Service Complaint but trying to disable roaming first the next time your there is a good idea.

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