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I'm helping my brother hook up a home network. He currently has cable internet service to one computer and digital cable TV to the remaining jacks. His current coax branching goes like this. Head end connects to a directional coupler Regal RDCT10-6. The output port has an Arcom WHP-5/13 return path "window" filter. This then feeds an amplified splitter that sends the TV signal to 8 rooms. The "tap" port of the coupler reduces the signal by about 6.5 db. The tap is then connected to a line amp that boosts the signal before that branch goes to his cable modem. Now this seems confusing to me. Why would the cable technician use a tap that decreases the signal and then add an amplifier to boost the signal? I'm not sure what the signal boost of the amplifier is. If it were 10 db, I guess that line would have a net increase of 4 db. But do cable internet connections require that precision of signal level? I'm tempted to do the following: Replace the directional coupler with a simple splitter that will only lose 3.5 db to the modem. Remove the line amp to the modem and see if everything will still work. What do people think? Is this a good idea or should I leave his setup alone?
I also am curious about the "window" filter that was placed before the TV runs. I believe you're supposed to place a high pass filter to help prevent noise ingress from ruining the upstream cable signal. I'm not sure, but maybe that filter also helps prevent the modem from degrading your TV signals. But why a "window" filter? Should I replace that with a high pass filter instead? Thanks.
No, leave the window filter in place. It will pass return signal from any set-top-boxes installed (between 5-13MHz) while preventing anything else outside that passband from entering the return path. A high-pass filter is not selective and would block all signals, wanted and unwanted, from entering the return path.
I'd leave the 6db directional coupler in place and remove the line amp. The amp shouldn't be needed unless your technician is trying to cover up a problem. This is the way my modem is set up and is a common installation practice throughout the industry.
Can you get to the modem's diagnostic page at http://192.168.100.1/ and read the up and down signal levels and downstream S/N?
Thanks buckifan. That makes sense about the digital set-top boxes. I guess they have to send return signals if my brother orders pay per view, etc.
Does that window filter also block unwanted transmissions from the modem to the TV branches, or would the window let that modem "noise" passthru.
I can check on the modem diagnostic page when I'm at his house, though I think he now wants to buy a new modem. He has been renting an RCA modem from Comcast for about 5 years. I think that modem has cost him about $180 so far. He'll probably buy a Motorola or a D-link modem at Best Buy today.
XrayDoc wrote:
Does that window filter also block unwanted transmissions from the modem to the TV branches, or would the window let that modem "noise" passthru.
The isolation between the directional couplers tap and out ports is very high so that would attenuate at lot of the modem's signal going toward the TV's. If the modem is using a return channel higher that 15MHz then whatever is left will be blocked by the window filter.
I can check on the modem diagnostic page when I'm at his house, though I think he now wants to buy a new modem. He has been renting an RCA modem from Comcast for about 5 years. I think that modem has cost him about $180 so far. He'll probably buy a Motorola or a D-link modem at Best Buy today.
I think a newer modem would be a good idea too. Here is Comcast's approved modems list.
so the "thorugh leg"of the dc goes to the modem and the tap goes to the amp-8way with a window filter before the amp? i would have got the boxes off of the amp to helo with the rdc but that's just me how many does he have? but the setup is the best for the modem....should be getting a ton of signal off of the dc..and an easy return..
