The coax cable (wiring) from the antenna to the TV may be bad or going bad and /or the signal amplifier may be going bad. Either of these can cause what you describe. You need to find out where the problem is before you can fix it or you can spend time and money and still have the same problem. I just had the badley weathered exterior coax replaced only to find my antenna amplifier actually cut out what signal there was when it was turned on. Fix was to replace the amplifier. Still have the old antenna which does not have much to go wrong.