Hi,

I am using sim900A module, for sending SMS , similiar to this:

http://www.aliexpress.com/store/pro...ard-better-than-sim300/835168_1328189947.html


1. problem is there is no datasheet available, all are either from china or taiwan

2. The antenna is very small. I have to increase the antenna length by 1m, is there antenna expander which I can use without losing the signal strength.

 

an antenna length of 1 mn would not work, the wavelength is much shorter. 900 mhz antenna is about 35 cm, and 1800 mhz is about 17.5 cm.
also, if you are in the US, it woluld be illegal to modify the antenna on the module.

 

1. then what is the maximum antenna lenght I could increase.

2. I have to modify the design for it. but current antenna is very small

Edit: as you had mentioned, is the actual antenna is maximum lenght I could have

 

Hello,

The used antenna is probably a helical type.
For "longer" antennas, you could have a look at the following sites:
http://www.tessco.com/products/displayProducts.do?groupId=253&subgroupId=21559
http://www.zdacomm.com/wireless-ant...ications/cell-phone-antenna-cellular-antenna/

Bertus

PS please obey the local transmition limits.