IF loop on modulator

[zenith2134]

I have got a number of agile modulators in use as short-range NTSC broadcast beacons. I have tried replacing the coaxial cable in the IF loop(s) with F-connector-to-phono-jack adapters & then using a high quality CVBS cable instead. It seems to have a better image quality on high contrast scenes this way.
Any reason this would be less than advisable? FWIW, the cord lengths are all under ~1 ft.