Thread: 622 coax output w/ RF combiner

I have Comcast cable TV and am using an RF combiner to combine it with the TV2 modulated output form my Dish Network 622 receiver. Previously I was feeding the cable signal from a passive 2-way splitter into the combiner and everything worked ok. I got decent signals from both cable channels and the modulated channel 80. I needed to change my setup a little bit to accomodate another TV, so I added a PCT 4 way amp to my incoming cable signal, which then feeds into the combiner. Now the cable channels look great, but the TV2 modulated channel 80 has a rather snowy picture. Can anyone explain why this is happening? Is the newly amplified cable signal so strong that it is interfering with the modulated channel? If so, could I remedy the problem by strengthening the 622 RF output with an inline amplifier or a 1 port drop amplifier?

I was also beating my head on that one until I talked with a friend who's a Time Warner tech in their NOC.
Guess what starts at CATV channel 80? Yup, the digital channel lineup that TW and Comcast send. What you are seeing is bleed-though of the digital noise on your combined network.

The way out of it is to get a Channel Plus low pass filter that takes out everything above 64 (I think it's the LPF-480) and that should take care of your problem. The way to test it is to leave everything alone and just disconnect (for a second) the input cable from Comcast. If channel 80 magically clears up then that's what it is.

What you've done is amplified the entire cable spectrum with the PCT amp (which BTW is a great amp) which then causes the digital channels to scream onto the cable. Another way to test this is to set your modulator to the lowest or highest possible setting and see if you can clear the digital channels.

The Channel Plus LPF-480 is a nice filter because it blocks everything above 64 but it allows 96-99 as cable providers put special programming on their like the Big 10 network, etc.

Originally Posted by bookworm370

I was also beating my head on that one until I talked with a friend who's a Time Warner tech in their NOC.
Guess what starts at CATV channel 80? Yup, the digital channel lineup that TW and Comcast send. What you are seeing is bleed-though of the digital noise on your combined network.

The way out of it is to get a Channel Plus low pass filter that takes out everything above 64 (I think it's the LPF-480) and that should take care of your problem. The way to test it is to leave everything alone and just disconnect (for a second) the input cable from Comcast. If channel 80 magically clears up then that's what it is.

What you've done is amplified the entire cable spectrum with the PCT amp (which BTW is a great amp) which then causes the digital channels to scream onto the cable. Another way to test this is to set your modulator to the lowest or highest possible setting and see if you can clear the digital channels.

The Channel Plus LPF-480 is a nice filter because it blocks everything above 64 but it allows 96-99 as cable providers put special programming on their like the Big 10 network, etc.

That's because 96-99 are lower frequencies (somewhere around ch14), It's also why the modulator on DISH receivers don't offer those channels.

Duhh,,,, you're right of course. I had a brain cramp.

91-115mhz for those channels. Thanks.

Originally Posted by bookworm370

The Channel Plus LPF-480 is a nice filter because it blocks everything above 64 but it allows 96-99 as cable providers put special programming on their like the Big 10 network, etc.

I looked at that, but won't it also filter out my digital locals? I would like to be able to pass both the analog cable channels as well as the in-the-clear digital channels. How well do the notch filters work? I have read some reviews about the filtering bleeding into channels outside the notch range, which could also cause me problems.

It depends where in the network you put the filter. Are your digital locals coming from an OTA Antenna or Comcast?
If OTA then don't worry because they are on UHF frequencies. You'd put the filter on the Comcast entry point.

If they are being sent via Comcast then you'd have to find out just what channels Comcast is sending them on. But considering that before you amplified everything was working fine, I think you'd be Ok.

Are you combining UHF OTA with the CATV cable? Your original post didn't say anything about how you feed the OTA free-to-air digital locals.

Channel 80 CATV is at 559.2500-563.7500 mhz. The closest UHF OTA are channels 28 and 29 (not sure of your local digital mapdown) at 555.2500-565.7500 mhz (spans the channel 80 CATV signal. If no one is broadcasting on those 2 UHF channels, you should again be ok.

The digital locals are coming from Comcast. I'm not sure where all of them are located, but I do know there are some on 81, 116, and 117. I think the
Channel Plus NF-471

would do the trick, but I'm afraid that is is going to bleed over into channels 74 and 81, which could cause me to lose the Big Ten Network on 74 and my digital channels on 81.

You probably considered this, but did you just think about changing the channel 80 modulated channel to something like 76 or 77?

Originally Posted by bookworm370

You probably considered this, but did you just think about changing the channel 80 modulated channel to something like 76 or 77?

Yeah, I tried some other channels and still get an equally snowy picture.