@David-TP Thank you so much for the information, Currently replacing both antenas with external antena will be costlier for me so i was thinking only add an extension cable to main antena only. and external antenas are very high priced and mostly not available in amazon so will it work if i add only one extension cable on main antena?

  @David-TP Hello theres update. im now using its antena outside and happy 10x than before. i took the risk of buying that cable wasnt sure it will fit but it actually does fit.

im now using its main antena outside only one thing is that using antena at that distant is not powerful and does not increase range much infact compare to placing router itself on the roof i get low signals but thats okay since i dont get Band 3 , 40 Inside my room at all. now using this method im able to get full signals of all avail bands inside my room with max TA. 

i placed my antena infront of my old DTH Antena Disk so the signals reflects from disk to directly antena and im getting max speed that i never imagined i could get ever in that area.