[Electron]

The antenna needs to be no less then 40 feet above ground. I use 3 channels as references. WSET 13 ABC at 20 feet the NM(dB) is minus -18.4 [Bad] , at 40 feet the NM(dB) is minus -11.8 [better] , at 60 feet the NM(dB) is mimus -10.5 [not much of a improvement and and buy it's self not worth going from 40 to 60 feet for].

The next channel is WBRA 3 PBS , at 20 feet the NM(dB) is plus + 30.3 [good] , at 40 feet the NM(dB) is plus +36.9 [better] , at 60 feet the NM(dB) is plus+39.2 [more better].

The next channel is WXFR 17 Fox at 20 feet the NM(dB) is plus +.4 [not good] , at 40 feet the NM(dB) is plud +9.1 [better] , at 60 feet the NM(dB) is 11.3 [much better].

So the antenna should be not less then 40 feet and up to 60 feet above ground. 40 or 45 or 50 feet will be fine.

And yes I recommend using the RG-11 cable.

The antenna must be higher. Getting the antenna higher is the most important action to take now. And use the antenna and amplifier you have now.