# feeding modulated ch4 into cable stream with internet



## Jodean (Jul 17, 2010)

Ran into a problem at a house i was at.

It had the cable modem split in one room along with a tv.

The room was over a very tight crawl space. The tv was a 13" old old crt.

The guy didnt want me to run a coax on the exterior of the house.

Even if i had a cable to the room, i would have used a modulator anyway ( no video input)

What i came up with is to modulate the receiver output, stick the receiver in the basement and combine the ch4 modulation into the cable/internet line.

This is working and the cable system had no ch4

Are there any problems with this setup that would cause problems down the road?

I used the already there splitter/combiner


----------



## litzdog911 (Jun 23, 2004)

This can be tricky. How did you "combine" the Ch4 modulated signal onto the Cable TV coax?


----------



## RobertE (Jun 10, 2006)

I hope you installed some sort of filter/trap to prevent your modulated channel 4 from backfeeding into the cable system. Otherwise I believe your poor customer could be subject to some fines.


----------



## ndole (Aug 26, 2009)

RobertE said:


> I hope you installed some sort of filter/trap to prevent your modulated channel 4 from backfeeding into the cable system. Otherwise I believe your poor customer could be subject to some fines.


Ut oh batman :lol:


----------



## Jodean (Jul 17, 2010)

No filter, will one "out" backfeed to the other "out"? From mod back out to cable like that?


----------



## BattleZone (Nov 13, 2007)

Jodean said:


> No filter, will one "out" backfeed to the other "out"? From mod back out to cable like that?


Yes, absolutely!


----------



## wallfishman (Dec 31, 2008)

all the extreme splitters i have seen and used from the cable company arent diplexers they are just regular cable splitters. did it say combiner on it? the cable co doesnt issue combiners or diplexers because they dont want the modem diplexed. you are backfeeding that signal onto the plant. a neighbor or someone will have issues because of it and they will end up sending a line tech out there to determine where the noise on the line is coming from. they will narrow it down to their house and they will try to make contact with them and if they are not home they will tag their door and let them know there is a problem. they will then put a high pass filter on the line which will stop all 2 way communication shutting down their modem and all digital boxes until the problem is fixed. 
what is a tight crawlspace ? was it carpet in the room or hardwood floors? alot of tight ones like that i drill down and shove a bunch of wire down into the crawlspace and then reach in there with long lay up sticks to get it and pull it to you. 
ive never done what you did there, the cable company dont want you doing that, dirtectv dont want you doing it and its just going to create problems.


----------



## Jodean (Jul 17, 2010)

they will more than likely put some kind of filter on, they are cancelling the cable service. Not sure how they do that but i assume a fitler will pass internet only to the house. Assume filter will be at pedastal.

Not sure why you would want a diplexor in this situation, a combiner is what is needed. Most splitters are also combiners.


----------



## scooper (Apr 22, 2002)

The "better solution" if you have to share the cable is to do the diplexer route - at least your DBS signals SHOULD be out of the frequency range of the cable company - and place the DBS receiver in the same room as the TV.

My real preference would be totally separate cables, if that could be arrainged.


----------



## bigglebowski (Jul 27, 2010)

Cable TV splitters ARE essentially combiners also. Ive worked in headends for quite some time and when we need to combine signals we use standard splitters to do this. If you open up a device that is called a combiner, at least in the case of passive ones you will find if you open them up they are essentially a bunch of splitters working in reverse. The point is as long as what you are combining are different frequencies you should be OK. You will still have the same insertion loss values as if the signals were going forward through the splitter. Like 3db for a 2way and 9db for an 8way (approximating). 

As far as is this the correct way to have done the install, this is probably pretty safe. You would think that if a customer was getting cable modem only service that the drop to the house probably has a cheap shotgun style band-pass filter that is blocking "TV" channels like chs2-70s. So if any of the ch4 signal that you have created inside the house is likely to get killed before it makes it back through the filter into the neighborhood. This is also assuming that the mod you used is NOT a high gain modulator like you would use in a headend that put out 40+db. Now that might be strong enough to make it past the filter at the pedestal/telephone pole. It would probably be too strong for the TV too making the picture look distorted. I would bet that is not what you used anyway. 

The way to be absolutely sure would be to put a ch4 trap on the line before you injected your ch4 (before first splitter). For example its common in a hotel environment to have the local cable co as your TV provider to all your guest rooms. However you can get HBO/Showtime cheaper from another vendor via satellite. Usually you trap out a channel that is less desirable from the cable co and inject your channel onto the line. Wouldn't be a bad idea to consult cable co on that, they may even recommend the type of filter to use. In fact they themselves do things like this because most cable co premium channels require a STB, so at the insertion point to the hotel they will have the filter I am talking about trapping the channel, then they modulate the STB output into the mod. This way the guest sets dont need the STB to get HBO. This is what you did without the filter.

The filters that are designed to do this are pretty expensive, because they have to COMPLETELY remove the channel so when you inject yours it will not have interference. The filter that is used also has to match the total bandwidth of the system. So in a modern system the filter might need to be rated to handle up to 750Mhz+, whereas many years ago a filter that went up to 450 or 550 would have sufficed. The channels used for cable modem signals are likely to be up above chs70+. In your case one of those shotgun style filter made for ch4 would probably be good enough. They may be cheap enough to warrant doing. Or you could get another filter similar to the one they used (high pass, low block), that blocks chs below the cable modem frequencies. So like a $20 filter instead of a $800+ filter. 

If you had a signal level meter designed for cable channels and you had access to the pedestal where their filter was you could check for ch4 at the street. Disconnect the line with the filter attached and see what kind of reading you got on ch4. Now if there was no filter then I would agree more with the others that this would be a problem with neighborhood. 

This also assumes that the ch4 modulator in use isnt noisy and creating noise on other frequencies besides ch4. This can happen, but if the mod you are using is relatively low gain, this would be unlikely. The other issue that could cause a problem if the drop feeding the cable modem was already at the low end of the signal threshold, adding splitters/filters could bring the signal level below an acceptable threshold. Since this is really only a single drop that shouldn't be a problem.


----------



## Jodean (Jul 17, 2010)

scooper said:


> The "better solution" if you have to share the cable is to do the diplexer route - at least your DBS signals SHOULD be out of the frequency range of the cable company - and place the DBS receiver in the same room as the TV.
> 
> My real preference would be totally separate cables, if that could be arrainged.


No dbs signal at all.....only ch4 from the modulator


----------

