Signal conflict?
in [Repair]
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From: Jamie on 7 May 2010 19:40 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.php?gclid=CJqVu-CYwaECFRRM5Qod0QigAw
From: Jeroni Paul on 7 May 2010 20:29 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.
From: mm on 14 May 2010 16:40 On Fri, 07 May 2010 19:40:52 -0400, Jamie <jamie_ka1lpa_not_valid_after_ka1lpa_(a)charter.net> 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.php?gclid=CJqVu-CYwaECFRRM5Qod0QigAw 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.
From: mm on 14 May 2010 16:44 On Fri, 7 May 2010 17:29:47 -0700 (PDT), Jeroni Paul <JERONI.PAUL(a)terra.es> 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.
From: Jeroni Paul on 17 May 2010 15:50
> 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. |