In sci.electronics.repair, on Tue, 18 Feb 2020 11:46:44 -0800 (PST),
"Ron D." wrote:

You need to post what you have.

If it's from yesteryear, I suppose it;s a channel 3/4 combiner possibly with an RF amplifier.

It used to be really easy to take the output of a VCR run it to one of these and combine ATSC RF channel 4 with the TV feed not containing channel 4 and just select it on your TV. It was like $20.00 USD or less.

To handle other devices, you used an RF modulator to take composite video and convert to NTSC channel 3 or 4.

Now it's way harder and way more expensive to convert to ATSC. levels will be lower, but there would be better immunity to dropouts.

ATSC 3.0 which is coming soon will make everything that you do obsolete anyway.

Only my DVDR tuner is digital. The output is analog, so I'm using Ch. 3
everywhere.

Thanks all. I started another sort-of related thread.