So, I purchased BNC compression fittings for my RG11 and connected everything directly (direcTV client box and 3 year old Sony 4k TV)

Initially it tested fine, and as far as lag goes, it was no problem!

Knowing that HDMI likes to stop working after it hasn't been used a few days (BTW what the hell is that about), I went back to the jobsite and tested it again. The first time, the screen was blank (no "no video signal" message on the TV) but then the picture finally locked in after about 30 seconds.

I tried switching video sources and powering up and down the system to test. On one attempt it gave me a white screen with horizontal lines at the top, but I could hear audio.
On the second time, it presented me with a black screen and no audio - but I do not get a "no video signal" message, so the TV seems to think it is locked onto something.

I'm assuming this is because I am at the end of the wire length spec. By any chance can this SDI signal be amplified?

As I'm writing this, I'm thinking maybe the DirecTV box is doing that annoying thing where it defaults to 480i and maybe this unit is not spec'd for 480i.