View Full Version : Injecting an analog CATV channel into a digital/analog hybrid system

10-18-2017, 01:27 PM
Well, back in the day, I would add my CCTV system and media player to my cable lineup on channel 88 and 96 by simply using an couple RF modulators and a 3-input cable combiner.

I had been running this setup since back in the day with no problems. Well, I cancelled cable about 8 years ago before it went digital. Now I finally decided to turn cable back on. Nowadays the signal is about half digital channels and half analog. The 88 and 96 come through just fine on the analog, just like they used to. But, it knocks out half or so of the digital channels. Is there a way I can fix this? Or is it just not possible to inject your own analog channels on a mixed digital/analog cable system anymore?

I don't know a whole lot about how these signals work, but I know many of you do, lol.

10-18-2017, 04:01 PM
Where are you, and what system are you on? Can you find on line a listing of actual channel use (maybe not)? I'm a bit surprised that the system is still half analog. If you are injecting only two channels, I think they should not wipe out a bunch of digital channels unless:
1) you are attenuating the digital channels too much in the process of combining with your signals
2) your setup is injecting your signals at too high a level, overloading something, and splattering the added analog across multiple channels
(2b) your modulators are producing harmonics that coincide with digital signals at higher frequencies

EDIT: to test for case 1, keep the combiner in place, but turn off your modulators - see if you are still losing digital channels.

Electronic M
10-18-2017, 04:39 PM
Are there analog channels on the cable that you don't like?...If so switch your modulators to use those and get the correct filters to remove those channels ahead of the injection point.

Nowadays if you have mixed signal cable anything not used for analog is likely being used for digital, and not just cable TV, internet, phone, on-demand, and other things get crammed down the pipe. If you receive any other services you could be jamming those too.

Be careful your not letting any of your local signal back feed down the line, or you could be interfering with other's service, and the cable co will come down on you hard if you do that (they will also, if randomly asked, discourage your system for fear it will interfere).

These days cable co's have filled their bandwidth to be competitive so finding a 'dead spot' to transmit is not necessarily practical.

10-19-2017, 09:51 AM
Be careful your not letting any of your local signal back feed down the line, or you could be interfering with other's service, and the cable co will come down on you hard if you do that

What could/would the CATV company do to come down hard? Would it be anything worse than disconnection of service? I'm not familiar with the laws regarding this, but I'm guessing there could be FCC fines, etc.?

10-20-2017, 08:40 AM
A splitter is a directional coupler (with equal loss on each leg). AND they make directional couplers with different values of attenuation in the "down" leg also.
If you are using a splitter as a downstream combiner, there is little or no energy returned to the upstream. It might be 60 db. down which is negligible.
It has to do with the way directional couplers work and the way energy flows thru the toroidal core.

10-31-2017, 10:45 PM
I would be worried about the signal getting out to the street and going to the neighbors TVs.Thats if there is faulty filtered pole equip passing the said .It could rise issues with the CC and the authorities and content providers if re transmitting TV programming. I would string another line just for that to be on the safe side.