5130 all of a sudden dual band??? Network mystery here......

[Thanh]

Hello :)

So i got this 5130, which is a GSM-1800 ONLY phone. I use a modified flash file, which still keeps it being a GSM-1800 ONLY, i guess :)

The SIM in that phone is from a GSM-900 provider (Thailand, "GSM advance" or "AIS", network codes 520-01) and the network actually USED is "DPC 1800" or "Hello", codes 520-18. This is possible because AIS bought that company a while ago and the two networks can roam with each other.

Yet on saturday,the following happened:
me and my boyfriend, who is using that 5130 at the moment, went to Mahboonkrong center in Bangkok. There, in the food court on the 7th floor, he wanted to make a phonecall, which he did. And after it, he placed the phone on the table, looked at it and then asked me "what the heck is that???".
I looked at the phone, and instead of the operator logo it displayed "TH 01". I know what that means - the phone seemed to have logged in to the AIS network, which SIM card is inserted. yet - AIS is GSM-900!
I took the phone, cranked up net monitor and went to investigate. And i found that in fact the phone was logged in to that network despite the fact it is GSM-900..!
A look out of the window (it was dark) made me discover the AIS tower just about 15 meters apart at the edge of the building. And i tought "maybe the signal is SOOOO strong that the phone "runs" on a harmonic wave" or something like that, and i kept the phone on the way home. But it hanged on to that network untill we reached our apartment, where in the lift it lost signal and at the room it logged back into the usual "DPC-1800" which then displayed the operator logo.
Now i did a phone call to AIS and demanded to speak with an engineer (which to my surprise was possible!) and that guy not only spoke english but also could assure me that AIS "nowhere in the entire country" uses GSM 1800 in it's own network!
Now, what on earth can cause a 1800-only phone not only to catch, but also to hang on to a 900 network??? This network (TH 01, or 520-01) never comes up on a manual network search.......

Or was there some sort of "frequency hop" caused by the athmosphere? I can remember this strange situation over a year ago, then with a 6510, where at my offce on a sunny day i had the name "Itineris" on my display, instead of my logo.... knowing Itineris as a french network, i was puzzled. I know that electro-magnetic waves can be reflected at the ionosphere, which enabled me as a CB-radio operator to have DX conversations, but normally a frequency of 900 MHz or let alone 1800 MHz can't be reflected anymore, and specially not if it is over thousands of kilometers! yet still my phone cought that net for almost 25 minutes, i wasn't able to make a call on it (beep beep beep) but i could send a SMS which got delievered with almost 3 hours delay!

Can anyone tell me what that was with my 5130..? I am thankfull for any information......

Kind regards......
Thanh

[maddog]

I know the engineer spoke to you but it really sounds as though they have brought in a few 900mhz transmitters. We have similar things here in the uk with O2 (generally 900mhz) but if you use a 5130 in the right areas it will say something like UK-10 on the screen and work but obviously thats just when you are near 1800mhz O2 transmiters.

[Thanh]

Hello :)
Thanks for the reply :) The situation reminded me of the german Telekom-network (T-D1) which was the first network at all that made use of the then-new ability of dual-band phones to automatically switch between fruequencies, when they introduced 1800 MHz towers in bigger cities as a "backup" of their generally 900 MHz network. But this one is different.

Not only did the engineer assure me that there are no 1800 MHz transmiters on AIS, but also - the phone kept this nework (AIS 900!) all the way from Mahboonkrong Center to Bangna, where we live, a distance, on road, of almost 25 kilometers. There are a few dozen towers to pass between the two locations, and only after losing network completely (in the lift of our place) it went back to the 1800 MHz system it normally used. And all the distance i let my boyfriend drive the car and i kept the phone in my hand, watching the netmonitor readouts to see if it will change from 520-01 to 520-18, yet it refused t do so, not even at receiption levels of -98 dB. Clearly, the network could not be received strong, not as it would on an equivalent 900 MHz phone, but still it hung on to AIS 900 all the way. And it wasn't the same tower, as the cell cordinates changed all the time. Also, no way that the Mahboonkrong tower could provide any signal in Bangna :) I think AIS would be happy if it actually could :))

Any other idea..?

Kind regards...
your Thanh

[Nanda]

You mentioned AIS buying the 1800MHz network. Maybe they have re-programmed some 1800MHz base stations to transmit as 520-01 (maybe they're simply re-naming DPC1800/Hello as AIS, just as T-D1 shows up regardless of frequency used).

[Thanh]

Hi N900anda! T

hank youy for the suggestion........ at first i tought so, too, as i have read the news that AIS will slowly "phase out" the GSM-1800 network because it's customers are running away due to no WAP, no MMS etc etc....... Yet the news did NOT say what AIS want to do with people who want to keep that network, such as myself. Maybe they give them new SIM's to be used in the 900 network and shut the 1800 down? Or, as you said, simply re-program the base stations to make them part of the "GSM Advance" net, which is the name of that 900-network frm AIS....
The situation is that my boyfriend is customer of GSM Advance, he got their SIM but using a 5130 at the moment, he uses the ability to roam within the GSM 1800 network. Now, i myself am customer of GSM 1800, having a SIM from THEM in my phone. I too use the roaming periodically, when at my office the 1800 is weak, my phone automatically catches the 900. But i see the change, my logo then disappears and it shows "AIS GSM" instead.
At that day, my boyfriend's phone clearly said "AIS" (TH 01) while mine kept displaying the logo - so i was still on GSM 1800 with their own base station. If AIS would have reprogrammed that tower, mine phone would have displayed "AIS GSM" instead, but it didn't........ and also the "TH 01" kept all the way down to Bangna, with terrible low receipton levels (net monitor rules!) but still staying connected......... While my phone also stayed in it's network, "TH 18" or "GSM 1800", with full bars shown.
Well, i guess this is a technical wonder of some sort, and next time we'll get there i will try to reproduce it.... and then check if the phone can manually change from that "TH 01" to "GSM 1800" and eventually back to "TH 01". Then i will know what happened........... hopefully :)

Kind regards....
your Thanh

[Thanh]

Hello again :)

I found out what it is, sort of. Been there again twice, once saturday, once tuesday. On sat had my boyfriend with me, 5130, netmoni on. Phone as almost predicted went into "Th 01" as soon as we reached the second floor of Mahboonkrong, and gave network "520 01" with a high receiption level. Well, it worked. On the way home i again watched the phone, again it kept that network till we reached home, then changed back to 520 18. Ok so far.

On tuesday i went there again due to some trouble with the activation of my new contract (CDMA). I had my own GSM 1800 SIM in a 8-year old Pioneer, definitely a GSM-900 phone, one of the first i guess. In the display was "Roaming" instead of "AIS" since it's a GSM 1800 SIM card, and it indeed roams on the 900 network. So, reaching Mahbonkrong, i turned that phone off and back on just to see what happens. Nothing........ after almost two minutes it came up with "DPC 1800"!!! I then had the "pleasure" to use this brick for several calls..... a phone with a totally downed battery, standby time 5 hours and non-stop talktime roughly 20 minutes, keeping a signal like a piece of rock and also similar heavy. Historic phone. But it kept the "DPC 1800" which then stated (manual network search!) "520 23" to my surprise. No worries. Mixed up totally, i tought. After half hour and few short calls the battery went flat and i kept it off for a while, and when i was done with my business, i am about to leave, and powered it up again. Again - two minutes waiting, and - DPC 1800! But as soon as i reached the first floor, the network got too weak and the phone returned to "Roaming" briefly before the battery went flat again.
Later that afternoon i again called the AIS guys and described the obvious mix-up and the engineer was very surprised, but he said they will look into it. Maybe the towers there are really screwed?

I have to explain something about Mahboonkrong. It is Bangkok's biggest mobile phone trading spot, with the fourth floor alone housing several hundred mobile phone stalls and shops. The dealers there sell phones in ALL available thai networks, that is AIS 900, AIS 1800 (DPC or "Hello"), AIS analog 900, Orange (1800), D-TAC 1800, D-TAC analog 800, Thai Mobile (Suthep) 1900, and Hutch CDMA. And at any given time there must be thousands of phones logged in to all of those networks, and of course ALL those networks have their towers on the roof of Mahbonkrong. Is it possible that they interfer with each other in a way that get's phones confused..?

Kind regards....
your Thanh