4G LTE and Extended LTE antennas not working - is there a way to run diagnostics on the internal antennas?

[QuestionMark 0]

Message: Hello!
I am located in the USA, and have the PRO1 on T-Mobile's network. Per the specs, this is a 5-G capable phone, as well as 4G LTE. We reside in an area where T-Mobile supports 5G, 5G Ultra, 4G LTE, and Extended Range 4G LTE. There are multiple, overlapping towers / antennas serving my home location. All antennas on each tower are broadcasting all frequencies.

Here are the bands / Frequencies in combination that the network supports:
LTE: Band 71 / 600mHz
Extended Range LTE: Band 12 / 700mHz
AWS (hot spot and internet): Band 5 / 850 mHz
Band 2 & 4 / 1900 and 2100 mHz
5G: piggybacks on the Band 71 / 600mHz
5G Ultra: Band 41 / 2500 mHz

As you can see, when comparing the specs for the phone, it appears all bands except band 71 are supported.
Preferred Network Type is set to: LTE/TDSCDMA/CDMA/EVDO/GSM/WCDMA
Enhanced 4G LTE Mode is toggled on
Automatically Select Network is toggled on and set to fast.t-mobile.us
The carrier shows both towers broadcasting all signals, and antenna directionality indicates dual coverage for my location.

The signal icon in the upper right corner of the screen has always shown 4G LTE -- until recently. Now it simply shows 4G and the signal seems to fluctuate from 1 bar to 4, sometimes dropping to no bars. Same physical location within my home office as always. We've already tried swapping the SIM card. No improvement. It's as if the device is not connecting on the LTE bands, and has fallen back to EVDO - the older 4G protocol.

1. This is an unlocked device - so - is there a diagnostic we can run on the phone or from another device to diagnose which bands / frequencies are operable and in use?
2. Can you elaborate on the antennas in the device - SN 3736ff88 - are the specific band/frequency combinations listed above supported?
3. Is there just 1 antenna for multiple frequencies/protocols, or a separate antenna for each protocol?
4. Is there a diagnostic to determine whether a hardware failure has occurred - perhaps 1 antenna has failed and that might explain the fallback to 4G ?
5. Any other ideas that come to mind would be very much appreciated !

[EskeRahn 5,469]

The Pro1 (nor the Pro1X) has never claimed to support 5G,,,,
But some frequency bands have been reused by carriers for 5G

[claude0001 1,352]

On 12/13/2024 at 5:56 PM, QuestionMark said:

Per the specs, this is a 5-G capable phone

Nope, it isn't.

On 12/13/2024 at 5:56 PM, QuestionMark said:

The signal icon in the upper right corner of the screen has always shown 4G LTE -- until recently. Now it simply shows 4G

My Pro1s (still on LineageOS 16 and located in Germany) generally indicate "LTE" or "LTE+", which are different variants of the LTE protocol. In areas where network coverage is bad, my phones drop to "EDGE" (2G, still available in Germany). You are supposed to be able to somewhat influence the protocol switching behaviour using the "Preferred network type" system setting, but I've never seen much effect while playing with this. For practical purposes, "4G", "LTE", and "LTE+" are pretty much equivalent, and indicate the Pro1 is operating at the fastest protocol family it is capable of.

Note that even while being connected via a (theoretically) fast protocol, your effective data transfer speed may still be reduced for other reasons (weak or noisy signal, too many other users on the same tower, throttling by provider). 

On 12/13/2024 at 5:56 PM, QuestionMark said:

It's as if the device is not connecting on the LTE bands, and has fallen back to EVDO - the older 4G protocol.

Note that pretty much any network protocol may be transmitted over any physical radio-frequency band. As older protocols are phased-out, their frequency bands become free for carrying new ones. Also, usage of frequency bands differs from country to country, as this is governed by national authorities. The same band that may be used for LTE in the US may still be occupied by 2G in Germany, or 3G in Scandinavia.

EVDO is part of the 3G family of network protocols. I believe it was shortly (and deceptively?) marketed as "4G" by some US networks ages ago, but not in the rest of the world as far as I know.

On 12/13/2024 at 5:56 PM, QuestionMark said:

Now it simply shows 4G and the signal seems to fluctuate from 1 bar to 4, sometimes dropping to no bars. Same physical location

The RF hardware of even a fully functional Pro1 is far from stellar. Using any App able to display the actual signal power of the radios, you'll see that the latter is rarely above -100 dBm, even if all bars are displayed in the screen corner. If your data transfer speeds are OK and your VoLTE works without interruptions, be happy and done with it. Sadly, there just isn't much safety margin in the radios for f(x)tec phones. When I'm on the move (Germany) LTE network interruptions are common with all three of my Pro1s.

If your connection used to be better at the same location, I'd just assume they changed something on the antenna towers. As @EskeRahn suggests, they might have fully or partly (via DSS) repurposed some RF bands from LTE to 5G. As a result, your Pro1 effectively would not be able to use those frequencies any more, and be forced to revert to one of the remaining LTE ones (which might have lower signal-to-noise). Not much you can do about that.

On 12/13/2024 at 5:56 PM, QuestionMark said:

Is there just 1 antenna for multiple frequencies/protocols, or a separate antenna for each protocol?

The actual antenna is the (segmented!) metal back of the phone itself. Depending on the carrier frequency, RF signals are picked-up from (or injected into) it at various locations via spring connector electrodes. The latter are distributed over three so-called "antenna" PCBs, named "main", "diversity" and "wifi/gps". The first two work in tandem to provide mobile-network connectivity. See the corresponding patent https://patents.google.com/patent/US20170117614A1/en for technical details.

Edited Monday at 03:09 PM by claude0001