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Signal conflict?

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.

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Reply to
mm
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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 .

Reply to
N_Cook

[...snip]

Two choices:

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

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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:

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or

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Reply to
UCLAN

Wrong sig! Sorry.

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.)
Reply to
mm

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.)

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.

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.

Reply to
mm

put a attenuator in the line ?

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Reply to
Jamie

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.

Reply to
Jeroni Paul

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.

Reply to
mm

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.

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

Okay. That is helpful. Thanks again.

Reply to
mm

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.

Reply to
Jeroni Paul

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