Samsung Galaxy GT-i9100T SII - 850MHz optimised handset Telstra - Optus reception problems

The Samsung Galaxy GT-i9100T

Shortly after the release of the original Samsung Galaxy SII (GT-i9100), a model purportedly optimised for the Telstra NextG network was relased. The designation for this SII is the i9100T.

Apart from modifications to the software and user interface, no other physical changes are visible. The only give-away sign is the printing of the Telstra and NextG logo on the back cover.


Problems when used with other networks

Most i9100Ts sold by Telstra and their authorised dealers are not locked to the Telstra network. In some cases, the handsets are sold outright, and those customers have used them on networks other than Telstra. With no network lock, the only main annoyance was the pre-loaded Telstra apps and other bloatware. These apps can be removed by loading a different firmware, or by rooting the phone.

Soon, many non-telstra users of the i9100T noticed the signal reception was not as good as it should be, and 3G / celluar data speeds were dismal. In many cases, instead of utilising HSDPA, the phone defaulted to the slower EDGE or GPRS, even when 3G networks were available. However, with a Telstra SIM card inserted into the i9100T, data speeds were normal. The tests were verified by installing the non-telstra SIM card into an 'international' version of the SII (the non-T i9100), where data speeds were noted to be normal and 3G networks were able to be utilised. The SII is a quad-band UMTS phone. So what is going on here?

Telstra's tweak on the i9100T deliberately degrades performance on non-850MHz networks?

It has been noted that when using a non-Telstra carrier in vicinity of a large city centre or CBD where most other telcos run an 850MHz network, network speeds were acceptable and 3G (UMTS) reception is available. This is the case with Optus' 900Mhz and Three's 2100MHz networks. However, when further away, 3G reception drops off markedly and eventually falls back to the 2G (GSM) network.

There have been reports the modem firmware on i9100Ts have been custom-made by Samsung at the request of Telstra. Some users claim that by re-flashing the modem firmware with a non-Telstra version solves the problem. Conflicting reports say otherwise, where it makes no difference.

The secret lies in the hardware. There is an antenna/USB/microphone circuit board assembly at the bottom of the phone, below the battery compartment. The board connects to the radio (on the main board) via a short coaxial cable. There are contact springs on the board to make a connection to the actual antenna element, which consists of silver traces on the speaker box assembly.

On the international i9100 handset, the board effectively has a direct connection between the coax and the antenna element. But on the i9100t, there is an extra component in between the coax and element. This seems to be a bandpass filter of some sort, that favours the 850 and 900MHz frequency. Any other frequency bands (1900, 2100, etc) will be severely attenuated.

But why use a bandpass filter? Maybe Telstra thinks that the other frequencies are generally useless because their NextG network runs primarily at 850MHz. By blocking other frequencies and only letting 850 pass through freely, it could improve the signal-to-noise ratio for use on the NextG network.


Papillon, Sat, 20 Jul 2013 12:09 am: Reply
Having almost reached the end of a post paid two year contract with Tel$tra with the Samsung Galaxy S2 I9100T handset on a MRO I've been thinking of switching to a more cost-effective carrier but numerous forums and this post warn me otherwise.

In fact, Tel$tra itself acknowledges that it has tuned the I9100T to UMTS 850 RF sensitivity - read the 'Testing times but it’s worth the wait' section in it's news article:

What a pity!

Jaya, Tue, 30 Jul 2013 12:33 am: Reply
Comment posted from IP Address has been hidden.

Alfred, Mon, 13 Jan 2014 11:41 am: Reply
I have a I9100T that works poorly on the Optus network. But, I also happen to have an I9100 version of that bottom circuit board. Wondering if replacing this board on a I9100T and flashing the phone with the I9100 modem will make my phone work with 3G on Optus network.

Or maybe it will blow up my phone's main circuit board.

Any ideas appreciated.


Denise, Sun, 06 Apr 2014 11:00 pm: Reply
Totally makes sense now why my daughters phone would only work on edge after changing to a Telstra sim as it was previously a Vodafone phone. It was fine with any Optus reseller.

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