Another approach I've used successfully: attach a ground lead to the coaxial shield at the point where it connects to your equipment. Wrap the bared end of wire around the coax a few times & cable-tie it securely, or use a small hose clamp. The other end of the ground wire connects obviously to ground: use your AC wall outlet's plate-mounting screw, or perhaps a handy ground post on your preamp, etc.
Realize that inserting back-to-back baluns results in several dB of RF signal loss: check your picture quality before & after to ensure that it hasn't degraded.
Realize that inserting back-to-back baluns results in several dB of RF signal loss: check your picture quality before & after to ensure that it hasn't degraded.