If the existing RG6 coax is intact, use it, why not?
Which antenna you are currently using? If not using any, make a DIY antenna such as Spider, and mount it on roof with temporary support, and connect to existing RG6 cable end at the roof. Do not add any amplifier. Connect room end of coax to your Dongle.
This way you can test with practically zero investment. Later you can go for further improvement by adding an amplifier and replacing Quick Spider by a commercial antenna.
QUICK SPIDER - No Soldering, No Connector
