Oh, I read 'extension cord' and was thinking 110VAC.Yeah, we did that in college with RG8. We needed some power up on the 4th floor roof so we wired up the RG8 feedline. "Git 'er done!" LOL (Oh, can it, we were VERY careful!)
Being plain old RG-8U solid poly dielectric type it's not so good when you're looking at 30m of the stuff. You'll lose half the signal at 200MHz and at 800MHz you'll end up with less than a quarter of what went in.
I wouldn't recommend it for AC mains wiring but don't put anything past those crazy college kids. Braiding several lengths together like a heavy rope I managed to tow a 3,458lb 1957 Chevy with it 40 miles or so before the lead driver got a little frisky and we had to stop and splice it back together. Come to think of it we were "that age" at the time... hmmm.
It has already been settled that you're looking at the wrong cable for that long a run so why are you not looking for lower loss cable? Of course you won't overload the R20 with a big attenuator between it and a less than unity gain antenna... sheesh! One thing that hasn't been mentioned but should be, a hand held antenna sucks raw eggs to begin with, it is only used for portable because of its small size. Aside from low loss cable you need an antenna right for the job unless you want to end up with less than you started with.
It has already been settled that you're looking at the wrong cable for that long a run so why are you not looking for lower loss cable? Of course you won't overload the R20 with a big attenuator between it and a less than unity gain antenna... sheesh! One thing that hasn't been mentioned but should be, a hand held antenna sucks raw eggs to begin with, it is only used for portable because of its small size. Aside from low loss cable you need an antenna right for the job unless you want to end up with less than you started with.