Short spaced TV stations...

[old_tv_nut]

During the phase-in of ATSC, there were precise offsets applied to minimize interference into analog stations. This was needed because of ATSC's use of a pilot carrier near the lower edge of the 6 Mhz channel. Offsets were controlled not only for co-channel, but anylowe r adjacent NTSC channel as well. ATSC 3.0, like DVB, uses COFDM, with multiple pilots at the same level as data scattered over the band, so the signal is very noise-like and no visible pilot beats would appear in an analog set. Of course, precision lock between ATSC transmitters is required if they are part of a single-frequency network (use of multiple transmitters to cover an area with a single broadcast on the same frequency), just as it is/would be with DVB.

[old_tv_nut]

Analog NTSC co-channel stations were offset by 10 kHz, which turned the interference from a wavering picture into horizontal sine wave "venetian blinds."

At least one company sold a filter that plugged into the back of a monochrome TV CRT (and the socket then plugged into the filter), which contained 10 kHz traps for the grid and/or cathode leads.

I don't know the electrical details, but I have seen pictures of one. Thought I might have a picture, but can't find one.

[ppppenguin]

Band planning for digital TV systems is very different to analogue. As others have said, a COFDM signal is very much like white noise over the entire channel. Single frequency networks are possible though not always used. There is no particular need to worry about adjacent channels.

If you're using analogue TV RF signals in your system (vintage or otherwise) then try to avoid any local digital channels. They look like white noise to an analogue set and a strong local digital signal can give you a very noisy picture. We suffered this problem at the Vintage Wireless Museum, London, when a new COFDM multiplex started up from the main high power TX at Crystal Palace little more than a mile away. We had to change to a different channel at the museum.

[Robert Grant]

Originally Posted by old_tv_nut

Analog NTSC co-channel stations were offset by 10 kHz, which turned the interference from a wavering picture into horizontal sine wave "venetian blinds."

At least one company sold a filter that plugged into the back of a monochrome TV CRT (and the socket then plugged into the filter), which contained 10 kHz traps for the grid and/or cathode leads.

I don't know the electrical details, but I have seen pictures of one. Thought I might have a picture, but can't find one.

To be effective, it would also need a 20kHz trap for when a plus offset and a minus offset station collide.

[Robert Grant]

Originally Posted by zeno

In the good old NTSC days WESH was the most common DX station
to be picked up in New England. Always in there with the slightest
sporatic-E. No other did this, it would be random from certain areas.

73 Zeno
LFOD !

I wonder if you lived in Hartford or Philly.

WEDU (Tampa, channel 3) was ultra-common, too, but WFSB or KYW have have drowned WEDU out.

Sporadic-E propagation in the VHF-Low TV band strongly favors paths of 1,000 miles (1,600 km), not much further, and not much shorter. If a TV DXer gets a station 350 miles distant, he/she will brag about it.