I am using an AIS SIM  card and on the packet it says Super Play 4G . I want to buy an external roof antenna to boost the signal . On the AIS web site it shows their 4G frequencies as -----

 

900MHz – 1800MHz – 2100Mhz 

 

I can't find just one external antenna that covers all the AIS 4G frequencies . So it looks like I have to use only one frequency .

 

How can I find out which frequency of external antenna I have to buy to match my current AIS SIM card. 

 

Thanks 

AIS will sometimes indicate the band in use along side the 'carrier label'.

For instance, on my smartphone it displays "AIS 2100" to indicate I'm connected to a 2100 cell tower. 

There are quite a few Android applications which can identify the currently used (and nearby) 3G and 4G signals. I would try a few of those with your AIS SIM installed, in/around your home, to identify which tower/service might be serving you.

 

example: https://play.google.com/store/apps/details?id=com.wilysis.cellinfolite&hl=en

 

But there are quite a few which should work.