Assuming you've aimed the antenna in the proper direction and there's not a huge obstruction immediately in front of it, you should be getting at least something with the ANT751, even on your porch. I suspect you have a bad coax or improperly terminated connector or balun.
Even if you solve your almost obvious cabling/connector problems, the antenna really needs to go on the roof, not the porch. You can buy antennas until you're blue in the face, but there is not a magic antenna that will solve the problem of putting it in a bad location (dead spot).
You need to get someone who knows what they're doing to install your antenna in the right location and do it correctly. Or sub to cable. But for what you would pay for a few months of cable, you could pay someone to properly install your antenna for you.