miketinte wrote:
I want to overlay an image or text (perhaps through CC programming?)
on all channels of my home's cable system (NTSC). What's the simplest
way to do this? Has anyone done something similar to this before and
can offer some sage advice?

Sort of...

http://www.decadenet.com/bob2/bob2.html
$79.95 each.
You program the text from your computer's serial port.
You would put one on each TV after the cable box, because it
has to work on baseband video not RF. I think this is the
simplest way and much cheaper than trying to do something with
each RF channel.
-Dan Barlow

Thanks for your response.

I was kind of going for a DIY (or solder yourself) type project.
Mainly because of costs involved with the pre-fab solution. Basically,
I want to display this image OVER the television show that is being
watched without any interruption. The trick here is, I want to inject
this image into the main splitter of my home's cable TV system. We've
gone almost totally DVD, so only one of the TVs in my house is a VCR
and anything involving a VCR is out of the question. How feasible is
this still?

miketinte wrote:
Thanks for your response.

I was kind of going for a DIY (or solder yourself) type project.
Mainly because of costs involved with the pre-fab solution. Basically,
I want to display this image OVER the television show that is being
watched without any interruption. The trick here is, I want to inject
this image into the main splitter of my home's cable TV system. We've
gone almost totally DVD, so only one of the TVs in my house is a VCR
and anything involving a VCR is out of the question. How feasible is
this still?

I would say possible but even more expensive.
The signals in the cable aren't "lined up" in such a way that
you can affect all of them at once.

You would have to somehow separate out each channel, get it down
to baseband NTSC, detect sync, put in either your closed caption
message or your overlay, convert back to rf, and combine each
channel at its proper frequency.

You can do the first part with a big pile of surplus cable boxes.
The overlay you can build yourself but it's a bit complex.
I did a quick Google search and there are a few projects out there
but most people have gone to using a PC video capture and output
card to do this kind of thing.

You can get a whole pile of RF modulators cheap as surplus too,
but the channels will all come out as 3 or 4.

Getting channels shifted back up to their original "address"
is going to be interesting. There are circuits to frequency-
shift a channel but they're not mass-market so they tend to
be quite expensive.

http://www.tonercable.com/Toner%20We...ON-OTM3550.pdf
http://www.multicominc.com/Manufactu...e/page%208.pdf

Then you use a big reverse-splitter to combine all the outputs and shove
it into your house's cable.

I don't want to discourage you, but this is in fact a lot more
complicated than you'd expect.
-Dan Barlow