mm wrote in message
...
What should I do about signal conflict (overload?) between two
sources, both on co-axial cable? Is there an easy way to weaken a tv
signal in a co-axial cable?

I have two inputs to my maybe 10-year old analog tv, selected with an
A-B switch, with co-ax input and output. One input A is from the
2-year-old DVDR with digiital output and an RF modulator in the other
room, and the other input B is a 1-year-old set-top box atop the set.

In the last week, when I am watching in the A setting and slide the
switch to the B setting to use the set-top box, there is an image for
a split second, and then the screen turns all blue. But when I
disconnect the A signal from the A side of the switch, the B side
works fine.

(This doesn't happen in reverse. The A signal will display fine when
the switch is on A, even if there is a B signal connected to the
switch.)

I've concluded that the A signal is combining with the B signal to
cancel both signals, or at least to change the signal such that the
static suppressor in the tv stops trying to display a picture and just
displays the blue screen.

When I disconnect the B and the A signals from the switch, it still
shows the A signal pretty well, I guess because all three co-ax cables
run side by side and the A signal must be stronger. Do you think the
signal is going right through the braid of the co-ax, or is it
sneaking out through the open end of the unconected F-connector?

Another clue is that I first noticed this a week ago, very soon after
the old RF modulator failed and I installed a Belkin brand RF mod. The
first RF mod lasted only two years. Maybe Belkin is a better brand
with a stronger output? Except now it is too strong for this setup.

Is there an easy way to reduce the signal strength of the A signal, or
can I get an A-B switch with greater separation? I"m using an RCA
brand (though identical switches are sold with other or no brand)
pretty compact A-B switch with a flat top and bottom that I like,
because it is stackable with more A-B switches. (At one point
somewhere I needed two of them.) I could change to another brand, or
change to a remote controlled Radio Shack A-B switch. Would that be
likely to help?


My original plan was to output one signal on channel 3 and the other
on channel 4 and use the tv remote to change channels, but iirc there
was interference between ch 3 and 4, and one or both didn't come in
clearly.

Then I tried just using a splitter to TV channel 3 and making sure
only one signal was on at a time, but one of the signals was too weak
iirc to work this way.

Then I got really cheap a device that, when a video game is on, it
takes the video game for input, and when the game is off, it takes the
other input. Unfortunately, this switching seemed to depend on some
sort of DC voltatage present in video game output, that isn't present
in either the set-top box or the DVDR output. (Does that sound right?)

So the A-B switch seemed straight-forward, but now this.

What would you guys do? Thanks.

--
Posters should say what U,S. state if any they live in. Why
do so many keep their state as secret as their own name?

IANAL. That is, I am not a lawyer.

Have you tried changing one or more of the modulator frequencies? usually a
recessed screw head near the connections, but put a sleeve over the
screwdriver before inserting .