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.

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 .

mm wrote:

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.

[...snip]

Two choices:

1) [Best Choice] Get a programable modulator that lets you choose any channel.

http://www.channelplus.com/product_d...?productId=224

Set it to a much higher channel. Tune directly with with your TV tuner. Use
signal combiner for A and B signals. Trash A/B switch.

2) Get a better A/B switch.

Or do it all with:

http://www.channelplus.com/product_d...?productId=170

or

http://www.channelplus.com/product_d...?productId=225

On Fri, 7 May 2010 11:22:26 +0100, "N_Cook" wrote:



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.

Wrong sig! Sorry.

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 .

Thanks.

I just looked on the settop box and didn't find any screw. Not on
the RF mod either, but it has a slide switch for 3 or 4.

The on-screen Settings for the set-top box only permits 3 or 4. At
least afaicr. Before I buy what UCLAN suggested, I'd better check
again. Yes, only 3 or 4. This was a fairly expensive one, Dish TV,
70 dollars (coupon plus 30 cash. It has features the others don't.)

On Fri, 07 May 2010 12:12:19 -0700, UCLAN wrote:

mm wrote:

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.

[...snip]

Two choices:

1) [Best Choice] Get a programable modulator that lets you choose any channel.

http://www.channelplus.com/product_d...?productId=224

Set it to a much higher channel. Tune directly with with your TV tuner. Use
signal combiner for A and B signals. Trash A/B switch.

Wow. At first I didn't like this because it meant spending more money
than a switch would cost, buying a whole new device, but A) it's only
aobut 50 dollars, B) one device would solve the problem at EVERY tv
with a set-top box. Right now there is only one, but I have two more
boxes to be connected. (I always imagine that something I've
never bought costs a lot of money. I was amazed when I saw how cheap
plexiglas and lexan are.)

2) Get a better A/B switch.

Or do it all with:

http://www.channelplus.com/product_d...?productId=170

This is only about 5 dollars more. I have to read the manual more
closely and also think about if I'm ever going to have a second
source. Or just assume I might someday and buy it.

or

http://www.channelplus.com/product_d...?productId=225

Hey, this is even better. This one has 2, 3, or 4 inputs, depending
on which model one buys, and costs 30 dollars more (78 to 100) for the
one with 2 inputs, and 102 to 120 for the one with 3 outputs**, 125 to
145 for the one with 4 inputs.

**(Geekbro has it for 184 dollars. You really have to be careful you
don't overpay. I came across a digital camera last month whose price
ranged from 80 to 280 dollars, same model, none of them
reconditioned.)

And yet they look like the first one you gave. The sketch in the
manual reminds me that maybe I will have satellite some day, plus the
dvdr (which has an antenna), and with a VCR too (although I would have
plugged that into the DVDR, it's good to be able to plug it into this)
and have those 2, or 3 or 4, inputs on separate channels, and still
just use channel 3 for the settop box whereever there is one.

I'm never going to have a camera at the front door, but one of these
is still the best for me.


Thanks a lot.


Even though now it's almost obvious, it didnt' occur to me that they
would make an RF mod with a different channel output, much less an
almost any channel output, and even multiple inputs, and even at an
affordable price. Wow. I don't think I came across these when I
was googling for RF mods, but if I did, their names or blurbs didn't
explain why I would spend the extra money.

mm wrote:
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.

put a attenuator in the line ?
http://www.e-meca.com/rf-attenuator....FRRM5Qod0QigAw

The switch for channel 3 and 4 is the modulator output channel, set
one to channel 3 and the other to 4. You can use a mixer (a passive
splitter reversed will do) to connect them to the TV, now you can tune
each. If you are planning to get a third box you will have to look for
a modulator that outputs to VHF III or UHF.
Keep in mind that placing these devices to standby will usually turn
off their modulador leaving free channels for other modulators and
will reduce wasted power.

On Fri, 07 May 2010 19:40:52 -0400, Jamie
t wrote:

mm wrote:
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.

put a attenuator in the line ?
http://www.e-meca.com/rf-attenuator....FRRM5Qod0QigAw

Thanks. I didn't know for sure they had something like this.

I have saved your post. I may need one later.

But I also didnt' know about RF modulators that would output to almost
any channel.

That will solve my problem both at this tv and at any other one in the
house if I connect a set-top box. And I'll be able to change inputs
by using the tv remote, which I already have, instead of getting up to
switching with an A-B switch, or buying one that works remotely.

On Fri, 7 May 2010 17:29:47 -0700 (PDT), Jeroni Paul
wrote:

The switch for channel 3 and 4 is the modulator output channel, set
one to channel 3 and the other to 4. You can use a mixer (a passive
splitter reversed will do) to connect them to the TV, now you can tune
each.

Thank you for replying. I had to read this a couple times to
understand and that's part of the reaosn from my delay in writing.

Now, which is better? Should I just say thank you or say that I had
done this before and it didn't work. I think the signal was too weak
from one or both sources after having gone through the mixer/splitter
reversed.

If you are planning to get a third box you will have to look for

Yes, a second box, but only for another tv, so still only two signals
at most at any one tv.

a modulator that outputs to VHF III or UHF.
Keep in mind that placing these devices to standby will usually turn
off their modulador leaving free channels for other modulators and
will reduce wasted power.

Okay. That is helpful. Thanks again.

Now, which is better? *Should I just say thank you or say that I had
done this before and it didn't work. *I think the signal was too weak
from one or both sources after having gone through the mixer/splitter
reversed.

By your initial post I guess you are using an A-B switch because both
boxes output to the same channel. Isn't it the fact? If you already
set them to different output channel and they still cause interference
it is either because they output a lot of harmonics (low quality
modulators) or the TV tuner cannot filter an adjacent channel
properly. In this case the solution would be to plug an external VHF
III or UHF modulator to the one causing most interference.