1957 Hotpoint interference when used on cable
 

Just got a 1957 hotpoint recapped and working.Model 14S202 UHF. Every cable channel,some more than others has intereference.It's clear as a bell when tuned in through a vcr. Is this the nature of some of these older tvs or will a tuner alignment help?So far I have gone through the IF alignment.It is about as close to the Sams shape and marker position as you can get and the picture is pretty darn sharp for a b/w tv.The sound is clear,no buzz and sync stable.

I haven't had cable for a lot of years; seems like shielding might be the biggest issue. I don't remember any special problems with a BW; when I last had cable I fought herringbone problems on all my sets, including the late models. I wouldn't expect that Hotpoint to be real tolerant of a marginal connection somewhere.

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make sure you have a good quality matching transformer on the set, good cables etc, agree with adjacent channel rejection, back in the day I seem to recal that most channels were always a couple channels away, example in sofla it was 4,7,10 for the CBS, NBC and ABC and a couple on uhf.

Have you tried a DTV converter box?

Portable TVs of the 50s were intended to work on a built in antenna so they had decent sensitivity. Channels assignments were alternated so adjacent channel and intermod rejection were not the primary design objectives. IF traps were fewer or often omitted altogether. The design served the intended markets quite well. What you see on cable would be expected in current conditions.

The VCR is operating with no other channels so it will not suffer interference. You could try padding the cable signal by about 20 db, or whatever it takes to keep just above the threshold of snow. That will reduce intermod and likely adjacent channel interference as well.

That's exactly what it is a herringbone pattern.

Checking the tuner alignment revealed that the tuner is very poor at rejecting adjacent channels even though the alignment is good.

Andy is correct about the poor selectivity of the tuners on older sets. In my earlier days(late 1960s, early 1970s), I lived in a part of Oklahoma where a relatively weak channel 9(CBS-OKC) was next to a very strong channel 10(ABC-Ada, Oklahoma). It was very common for the ABC channel to bleed into the CBS channel on the TVs of the time. This was over the air-not cable.

When I first used to read Consumer Reports magazine in the early 1970's, this was a frequent problem with sets they tested. They would specifically warn of likely problems with "cable TV systems that use all available channels". I guess that means some cable systems left adjacent channels blank at that time (and, of course, the system would have not gone above channel 13); when I first had cable TV in the mid-1980's, every channel was used.

To mostly get around this, I use a modern VCR as the cable tuner for the older TVs that have the biggest selectivity problem.

I have found that the RCA's with the Nuvistor RF amplifier seem to have pretty good selectivity, while cheaper sets like the GE Portacolor are very poor.

The early Hotpoint portable should be measured on second adjacent channel. All adjacent channel measurements should be 2 signal method with a modulated signal on the primary channel and continue to apply a second modulated signal on the adjacent (or second adjacent channel for older TVs) channel while watching (measuring) the measured channel for degradation. The difference in dB is the adjacent channel rejection characteristic for that receiver. For accuracy, there should be sound and color carriers as well. The result will vary widely from 2-13.

The original channel assignments left space between channels in the same markets. VHF was usually alternates. Four and five and 6/7 were exceptions due to band space between them. UHF was initially 6 channels apart. As cable became more popular, manufacturers had to improve selectivity so later TVs will perform much better on today's cable systems.