i think you are misstating a device or a jack.8dalejr.fan said:
rf out of a vcr can go directly into a cable/antenna input of a tv set.
you may mean video/audio out on dvd/vcr into rf modulator.
i don't know your unit but all vcr i've seen have an rf out and
except for the earliest ones a video/audio out. if it's a
dvd/vcr then the couple i've seen all have rf out.
the rf modulator would be needed for dvd player which only
have video/audio out to go into older tv which didn't
have video/audio input.
whenever you put stuff/devices in together you will deteriorate
the signal by both decreasing it and adding noise/interference.
every device, piece of cable, adapter, splitter causes deterioation
of the signal.
if you use the tuner in the tv to select channels then the signal
may be weak and give a grainy picture. if you use the vcr to
select channels (and in your case, with no video/audio inputs
on tv just antenna/cable input, so tv is tuned to channels 3
or 4 (in USA)) then you may get better picture for two reasons;
the vcr amplifies the signal and usually vcr tuners are much
better than tv tuners (especially older sets).
like others have said the flicker you see when swithching off
vcr is not a problem.