Humble request: When you ask a question, tell the reader what you are trying to accomplish first, and then provide the details, not the other way around. I really hate reading such questions started at the bottom.
Any reason you don't want to disclose the brand and model number? There are literally hundreds of different mutations of RG-6/u with a wide assortment of characteristics and deficiencies. Sometimes, I'm thankful the Radio Shack is gone as their RG-6/u was abysmal with an outer braid that was more decorative than functional, and a foil layer that had a small but leaky slot due to lack of foil overlap.
Try a terminating resistor, not a short or open. See: "Coaxial Cable Leakage"
I'll spare you my rant on what I think of measuring signal levels in S-Units:
3 S-Units = 0.8 uV 6 S-Units = 6.3 uV At 6 dB per S-Unit, that's quite a range of leakage.
Yep, because you've created a loop where the coax is grounded at both ends. If you want to ground the far end, you'll need an isolation xformer at the receiver with no continuity between the shields.
Same problem as before, except instead of 200ft of RG6 from receiver to ground, you now have a shorter length of coax involved. It still a ground loop, just a smaller one.
Ok, you have leaky coax. Dig out the data sheet and calculate the shielding effectiveness of your RG-6/u cable. The reason I wanted to know the signal level in uV at the receiver is so that I could calculate the shielding effectiveness. If you could provide a reasonable guess for the field strength of whatever radio station you're using for testing in mV/meter, and since we know the coax length, I could calculate how much I would expect the center conductor to pickup through the shielding.
These might help (or be of interest): "AM Radio Field Strength Measurements with Confidence"
Field Intensity and Power Density:
Note that EVERYTHING assumes that the coax is properly terminated. Forget about testing with opens and shorts on the end of the coax cable.
Methinks (not sure) that's because the chokes don't do anything once the RF leakage has arrived at the center conductor.
That might help if you isolate the grounds across the isolation xformer.
Note the insulation between each shield: If it really is leakage, it certainly will help. If you ground alternate shield layers to each end of the cable, then there are no ground loops. It probably also has lower leakage at 1MHz, but I'm too lazy to look it up. Might be worth a try.
Terminating the far end should have helped. Perhaps it's not really leaking through the RG-6/u but rather directly into the receiver through the case?
Terminate the receiver input with just a 50 or 75 ohm termination. Make sure it's shielded. If it still leaks, then try to determine if it's leaking through the AC power line, or directly through the plastic case. If necessary, put the receiver inside a metal box, and see if that helps. If the power line leaks, try running the receiver on a battery, or add a power line filter: In other words, forget about the RG-6/u until after you've leak proofed the receiver.