When you scan wifi, this does not related too much to your antenna. Because your antenna is only used receive signal. Whether you can find more signal really depends on the hotspot’s antenna TX power. Your big antenna can only detect sightly more signal because its RX is slight better.
Usually for using high gain antenna, you use a pair. One is used in the hotspot side and one is used in the client side.
Quick additional question , If I add something to boost my receptor TX power from 18 dBM (GL-AR150) to something bigger like 30 dBM like this: External USB WiFi adapter Tube U (N) Alfa Network , will I improve the range or this won’t do anything better as the limiting factor is the hotspot side ?
( I only control the receptor side of things, I’m on a sailboat and I use this to connect to coastal wifi hotspot )
I use external antennas on many GL units. Many have SMA connectors already on them, and others have u.fl connectors inside where you can modify the unit to have a u.fl to SMA cable. Many GL units accommodate this by making punch out holes available for the antenna.
Something like this
Edit: watch out for RPSMA!!
Can make a great deal of difference. If you are particularly good with RF cables you can try something like this for extreme range -
Many people make their own -
I have achieved range over 1 mile with 20 foot pole and external antennas with GL products.
This being said, you can also make things not work at all by connecting incorrectly or damage your unit. I started with Mango’s because they were inexpensive and small … YMMV. Search a lot and you may find a reliable solution for you.