Multiband GSM
From ShadoWiki
Check with your provider to see if you can take advantage of one band (say your voice is on one band and the data is on another, or both just on one band) and cater to the band you want to improve.
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Single Band GSM
For those of you lucky enough to know for a fact that your GSM phone uses, simply follow the directions for the sprint 1900 antenna but replace the 1/4h measurements with these:
* 850 MHz = 3.3"
* 900 MHz = 3.12"
* 1800 MHZ = 1.56"
* 1900 MHz = --> Just follow the Sprint 1900/GSM 1900 plans.
Remember the pen casing should be a little more (1/4") than 2 times the 1/4h measurement.
Dual Band GSM
Folks in Europe and the Pacific Rim probably use 900MHz/1800MHz, and by using a slightly longer antenna than the Sprint 1900/GSM 1900 (use 1.56" insead of 1.47") you guys can cover both freq's.
In the USA Dual Band GSM usually means 850MHz/1900MHz. Here you run into probelms... because they arent even multiples of each other you have to make compromises. Do you favor one freq at the expense of the other, or try to build an antenna that favors neither. I reccomend building a Sprint 1900/GSM 1900 .
Tri Band GSM
In the USA this usually means 850MHz/1800MHz/1900MHz, but really could be any three of the 4 GSM freq bands. My reccomendation would be to follow the Sprint 1900/GSM 1900 plans and use 1.56" as the 1/4h measurement. This splits the difference. By building a 1800MHz antenna you are only 100MHz off the 1900 MHz band, doable with reduced performance, and 100MHz off the first multiple of 850MHz (850*2=1700 MHZ) again doable with reduced performance. 1800MHz is also a the first harmonic of 900MHz and would cover it just fine if you use that freq.
Quad Band GSM
These Phones can use any of the GSM Frequences 850MHz/900MHz/1800MHz/1900MHz. If you wanted to try to cover all 4 of these frequencies then my reccomendation would be to follow the Sprint 1900/GSM 1900 plans and use 1.56" as the 1/4h measurement. This splits the difference. By building a 1800MHz antenna you are only 100MHz off the 1900 MHz band, doable with reduced performance, and 100MHz off the first multiple of 850MHz (850*2=1700 MHZ) again doable with reduced performance. 1800MHz is also a the first harmonic of 900MHz and would cover it just fine.
The GSM Solution
Unless you are targeting a specific frequency that you know to be used by your provider, there is a trick into making a "SPY 2.0" antenna work on your GSM phone. nonobeez from the forum has reported that he has had success with a custom antenna on a GSM Treo 650.
nonobeez: "hehehe... my GSM phone works great!!! I can stream 160kbps audio streams great (at night). right now I am getting 3-4 bars on the bart train. drops to 0 in the tunnels, but the LED stays green except on the long tunnels. the key to GSM is to stick to 1900 only."
The probable reasoning behind this is that the phone selects the best availiable frequency to use, and by giving it a good frequency range to select from it will select from that frequency. To accomplish this simply pick a freq range that your service provider does use, nonobeez and myself (spymongoose) recommend using the Sprint 1900/GSM 1900 frequency, and build the antenna.
