i also followed your suggestion as you see in the picture of 7 round / turns on the outside antenna and 5 on the inside.
I made it. There may be a only a tiny improvement in signal. I found the strongest signal location to be the east side of my house. 15 meters of cable between the outside antenna and the inside antenna which i placed in the middle of my house ground floor on the ceiling. Any suggestions on how i might improve my results? If i shorten the cable will that improve my inside signal strength? its much too long.
DIY 2G/3G/4G wireless cell phone signal booster