shreyas1 0 Posted April 11, 2009 Hello! I have run into an issue with a customer install using a Channel Plus modulator in a home. All the cable lines are home run, and are distributed. The incoming cable line and the modulated signal are connected together using a combiner, and then fed into an amplifier, then distributed to the home. I have noticed that when the modulator is running without the cable line hooked up, the signal is perfectly clear (running on ch 80). Once the cable line is added to the combiner, the modulated ch (80) shows a great deal of static. I'm unable to figure out what the problem is. Has anyone experienced this? I have tried multiple modulators, but it seems that the same issue occurs once the cable is introduced. Any help would be greatly appreciated! Share this post Link to post Share on other sites
DaveM 0 Posted April 11, 2009 I can think of two reasons this would be happening. The first is that even if the cable company doesn't broadcast on that channel, they have amplifiers all the way down the line that are doing their best to amplify whatever noise is on the line up to the "proper" value. You would get a great signal of the snow. The other is that even if you don't see a picture on the TV, they might have digital channels on it. You would need to scan the cable with a digital TV that has a menu to show what channels the broadcasts come in on. The only sure way to do it is to put a trap in line to notch out a section of the cable. You will loose any regular and digital channels within that range. That is what I did, and it works pretty well. I actually split the cable when it comes into the house, put the trap in line with one leg and combined the CCTV with it. That line runs to all the TV's in the house through an amplified splitter. The other line without the CCTV I've run with a separate cable run to a couple of the TV's with an A/B switch on it so if there is program on the notched out channels that I must see I can get them (hasn't happened in 2 years). In any case, be sure you either put an amplifier or notch filter on your cable line so you don't backfeed your camera out to all the neighbors TV's as well. One last thing, make sure that the signal from the Cable isn't so strong it interferes with the Modulator signal. A CCTV signal meter is great for this, or you can get a couple of variable attenuators from Radio Shack and turn the signal down on each feed until you start to get snow, then bump it up just a bit. Share this post Link to post Share on other sites
shreyas1 0 Posted April 11, 2009 I think I'm going to go the route with the notch filter. I spoke with the homeowner who said that the issue just started a few months back, so I'm going to assume that either the Cable co has put some digital channels on it, or like you said are amplifying the entire series of channels. Luckily, channels 75-80 are not currently being used on the homeowners TV's, nor do they have programming offered on them. Also, the current modulator is set to run on Ch. 80, which is even better. Thank you for your help. I'm going to order a: Leviton Passive RF Notch Filter 75-80 47690-NFA This seems like it will work. Let me know what you think though. I'm a little confused on what you mean by putting an amp or notch filter on the cable line to prevent distributing the signal outside of the home. Would using the notch on the main cable line, then combining it with the modulated signal and then feeding the amplifier and distributing to the home cause this ffedback? I'm assuming that it wouldn't, but please let me know if I have it wrong. I truly appreciate your help, I was completely stumped, but this seems like the most logical solution. Share this post Link to post Share on other sites
DaveM 0 Posted April 11, 2009 If you take the incoming cable and just combine it with the modulator signal the signal will go back up the cable line as well as down to the TV's. Close neighbors might be able to see your pictures. If you do this with a TV antenna it is possible to be "broadcasting" your channel at a very low power. If you put a notch filter in line it will block the TV channels coming in as well as your CCTV channels going back out. If you don't do a notch filter then putting an amplifier in line effectively blocks anything from going back out the other way. The filter you are looking at will not work well for channel 80. They spec it out as blocking 75-80, but it is not a very sharp cutoff. You will be able to put a signal on channels 76 and 78, or 77 and 79 with that filter as you will still get interference from the cable on 75 and 80. Reprogram the modulator to another channel and you should be good to go. Share this post Link to post Share on other sites
shreyas1 0 Posted April 12, 2009 That's what I figured when I started looking around at the different models. There would only be 1 actual channel lost, so that shouldn't be a problem. The modulator that is currently there is an older ChannelPlus, Model:4231. I can't seem to find any buttons on it to program the channels. It is a 2 channel modulator feeding channels 80 and 89. Any advice on where/how to change the channel settings? I'm assuming that it has dip switches inside, but I'd still be at a loss for what combination without the manual. Thanks again! Share this post Link to post Share on other sites
shreyas1 0 Posted April 12, 2009 Actually I was just messing with it on my workbench and managed to figure out the settings. The face comes off and there are 2 roll-selectors for each input. Looks like everything should be good to go form here. Thanks for all the help and advice! Share this post Link to post Share on other sites
scorpion 0 Posted April 13, 2009 Also note that there may not be any TV shows on selected channels, but the cable company may be using that channel for stuff such as guide info, or to control DVRs, and on demand video, and such. The modulator should have a dial to control the output level. The trick to this is to control the amplifier with the cable feed, and the modulator to get an even "teeter totter" effect. To much cable signal, and then you have snow on the modulated, and too much mod signal then you start killing digital channels, or hi def signals, and/or you lose video on demand, and guide functions. Share this post Link to post Share on other sites
scorpion 0 Posted April 20, 2009 http://scorpiontheater.com/wiring.aspx http://www.channelvision.com/ http://channelvision.com/ Affinity Digital Cable Combiner http://www.channelvision.com/products/index/88 http://www.channelvision.com/products/view/427/88 http://beta.channelvision.com/uploads/1215557281_P-0321_MixedSystem.pdf GUIDES: Diagrams and Layouts http://www.channelvision.com/files/guides/diagramsLayouts.pdf Filters and Digital Cable Support Guide http://channelvision.com/files/guides/Filters_And_DigitalCable.pdf Modulation Methods http://channelvision.com/files/guides/ModulationNotAvailable.pdf Satellite Guide http://www.channelvision.com/files/guides/satelliteGuide.pdf Share this post Link to post Share on other sites
