|
Sets made before about 1970 were not designed to operate with adjacent channels, since the FCC never assigned them to the same market.
The bandpass circuits in the tuner still pass a significant amount of energy from the adjacent channels into the mixer, which can result in all sorts of unwanted products, many of which are visible in the picture.
Cable, of course, uses all the VHF channels. For this reason many early sets will not operate well with a cable input, even if the tuner is hit with the proper level. I was in the cable TV business from the mid 60s, and it was always a challenge to get the older sets to work decently.
The solution is to use some device that outputs only one channel, such as a VCR, cable box, or standalone modulator.
|