I managed to sort the flickering it was due to a firmware conflict, did a firmware upgrade and its cured the problem.. I'll have a look at the gains on the modulator thanks...
it goes to quad as there are loads of equipment that needs the camera feeds its all linked in with thermal images, remote video unit, also a second set of coax for each camera for some reason? looks like he had two dvrs at some point who knows why? I love sorting out other peoples work haha! not!
Cheers bud
Kev