In post #98 of this thread
http://talk.maemo.org/showthread.php?t=31284&page=10
I try to address a comment made by Christexaport as to the inter-workings of the 2100mhz band.
Now it's got me to thinking;

1) Can a knowledgeable person inform us of the differences between UMTS Band I and UMTS Band IV?
2) T-Mobile-U.S. does use both the 1700 and the 2100mhz bands for up and down 3G transmissions, correct?
3) Is the 2100mhz capability of the N900 compatible with both the U.S and the European/Asian protocols?

I would assume that the answer to #3 is "yes," but I would like a technical explanation.

It is not as simple... Please take a look at this.

EDIT: To add a bit to this... The downlink (tower to mobile) bands are compatible between North America and Europe, but the uplink (mobile to tower) are different. The T-Mobile USA uses the 1700MHz band for this, while AT&T uses 1900MHz band as far as I know. In Europe the uplink is slightly below 2000MHz. (And then there is the European 900MHz band that is used in many rural areas.)

Here's the skinny. TMobileUSA uses both frequencies, and you can't get by with just one, because one is for up and the other down. We in the US call 1700/2100 TMobile 3G because they are the first to use this frequency, and currently the only ones with a network deployed afaik. (This is why I confuse some by calling the N900 a TMobile device. In the Americas, its the only carrier that can provide consistent 3G.

at&t uses 850/1900, and uses each frequency on the up and down. Some markets are purely 850, some are 1900, and some have both, so you can get by with one of either bands, but connections are hit and miss. The N900 supports none of its 3G frequencies anyway, just EDGE data, so its a nonconversation.

I'm only stating what I've "learned" from investigating this myself over the years, but the 1700/2100 for AWS won't be compatible with the 2100used in Asia. The reason why is this:

UMTS IV is what Americans call AWS or TMobile 3G. It uses 1710 - 1755 MHz on upload channels 1312 - 1513, plus 1662, 1687, 1712, 1737, 1762, 1787, 1812, 1837, and 1862,

...and 2110 - 2155 MHz on download channels 1537 - 1738, plus 1887, 1912, 1937, 1962, 1987, 2012, 2037, 2062, and 2087.

Now UMTS I is what the world considers IMT 3G . It uses 1920 - 1980 MHz on upload channels 9612 - 9888,

...and 2110 - 2170 MHz on download channels 10562 - 10838.

So unless the WCDMA radio in the N900 can handle 1710 - 1755 plus 1920 - 1980 on upload channels 1312 - 1513, plus 1662, 1687, 1712, 1737, 1762, 1787, 1812, 1837, 1862, and 9612 - 9888,

...AND 2110 - 2170 MHz on download channels 1537 - 1738, plus 1887, 1912, 1937, 1962, 1987, 2012, 2037, 2062, and 2087 PLUS 10562 - 10838,

...it won't cover all of the markets everyone assumes. This is why I still think Nokia must expect a subsidy from TMobileUSA somewhere down the road, or are using this as a measure to see how fast it will sell in the US on TMobileUSA with no subsidy.

So the 900 is just for European, Australian, New Zealand, and Asian 900 MHz markets and TMobileUSA, based on frequency. Or its not AWS at all, and just a weird combination of frequencies. Or maybe Nokia has expanded the width of the radios to adress the problems of compatibility between UMTS I and IV.

So we can assume the 900 MHz is GSM Band VIII, for Europe, Asia, Australia, New Zealand.

We can also assume the 1700 MHz is for Canada and the USA.

The question no one has asked Nokia is whether the 2100 MHz frequency is Band I AND IV compliant, or only Band I, or only Band IV. Any Nokians have the inside scoop?

There is no reason why the radios should not work in each market. They are tunable via software, and as long as the frequency is in the "band" of frequencies (ie the "2100" band, the "850" band, etc) it will work just fine since the antenna is of proper geometry to properly receive signals in that slice of spectrum.

The frequencies chosen by Nokia were to "harmonize" as many markets as possible with a single device configuration in order to reduce launch costs. If T-mobile picks it up on subsidy, so much the better. If you'll notice, the N900 being offered on the U.K. site is 900/1700/2100 as well. Does it make more sense that there is a single device capable of working across Europe/Asia as well as North America/AWS, or do you really think that they made two separate versions with the EXACT same 3g bands built-in...which would only work in one market or the other (with the european version having a useless 1700 radio). As I've pointed out in other threads...Occam's Razor rules the day. 2100 is 2100 is 2100 as far as the hardware is concerned.

Most of the world's 3G operators use 2100mhz UMTS:

http://en.wikipedia.org/wiki/List_of_UMTS_networks

I think a brief glimpse of this list should make it crystal clear of what kind of 2100mhz Nokia would and should support on any of their 3G handset.

I agree, Texrat, but only if the WCDMA radio supports both bands and applicable channels.

"...AND 2110 - 2170 MHz on download channels 1537 - 1738, plus 1887, 1912, 1937, 1962, 1987, 2012, 2037, 2062, and 2087 PLUS 10562 - 10838, "

I'd always been told that the TMobile 2100 wasn't compatible with the "Asian" 2100, but I'm not for sure.

I don't think they have made a separate device for markets outside of the US, but unless the 2100 MHz radio supports Bands I and IV, which no one has confirmed so far, I expect they would. Otherwise Asia is also shut out.

I'm also shocked that they have left at&t and a majority of the 3G Americas markets untapped. It doesn't look like Nokia intended any Americans to have the N900, but the AWS inclusion says at least a small, albeit good, part of the US was important.

As far as offering the N900 everywhere in its current configuration, I and many others will buy it with or without 3G connectivity, and maybe Nokia knows that. The original Maemo tablets had no 3G either, but they sold ok. As long as it has wifi, it has a place everywhere. I don't even plan to use a SIM when mine arrives.

But that's Band I, not Band IV. Can one radio cover both bands? It should, as Texrat says, but can that be confirmed? Because some TMobile hardware won't work in Asia, I've heard.

Baseband UMTS chips tunable via software? That's news to me. Do you have a link?