RF Modulator + Low Pass/Notch Filter vs. Digital Cable Channels? - AVS Forum
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post #1 of 12 Old 01-03-2008, 09:01 PM - Thread Starter
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I'm revamping my home video distribution system and wondering about the best approach for using a RF modulator in the future. Currently I have a single HDTV fed from a Cox cable DVR box (SA 8500HD) next to the HDTV, and mirror the DVR output to multiple other SDTVs via a RF modulator (Ch 125) and a low pass filter, combined with the Cox analog channels, over the home coax distribution system. I expect sometime in the not too distant future to have a mix of additional TVs, some with clear-QAM capable digital tuners (and maybe some additional Cox digital STBs). Will the low pass (or notch) filter + RF modulator approach block some/all of the potential digital channel reception? If so, what other alternatives would I have for mirroring my DVR over my coax distribution system?

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post #2 of 12 Old 01-04-2008, 04:06 AM
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Will the low pass (or notch) filter + RF modulator approach block some/all of the potential digital channel reception? If so, what other alternatives would I have for mirroring my DVR over my coax distribution system?

It will depend on the frequency of your filter and modulated channel, if those frequencies are being used the answer is yes, if not no!!
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post #3 of 12 Old 01-04-2008, 07:16 AM
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As was written, it all depends. Maybe yes, maybe no. Not knowing what is going to happen with digital channels, you may find yourself changing channels on your modulator more than once.

If you wanted to spend a few hundred bux, you could get a Channel Elimination Filter for an analog channel you never watch (the lower the better) and get a modulator for that channel.

CIAO!

Ed N.
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post #4 of 12 Old 01-04-2008, 08:56 AM - Thread Starter
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I was thinking lower is less likely to be a problem, too. My current modulator is selectable from ch 77-125, and I've seen several notch filters for ch 77-78, so I'm thinking I'll try that for the time being and see what happens with Cox cable.

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post #5 of 12 Old 01-04-2008, 07:43 PM
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Originally Posted by ratz View Post

I was thinking lower is less likely to be a problem, too. My current modulator is selectable from ch 77-125, and I've seen several notch filters for ch 77-78, so I'm thinking I'll try that for the time being and see what happens with Cox cable.

For lower, I meant such as 2-6. Channel 77 is still in the digital only bandwidth. Channels 2-6 are going to stay analog for some time to come.

CIAO!

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post #6 of 12 Old 01-04-2008, 09:41 PM - Thread Starter
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OK - got it - that will take a different modulator for me, but I appreciate the info so I know what to look for.

Thanks!

Phil
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post #7 of 12 Old 12-17-2008, 11:39 AM
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Ever follow through? Success?

I'd like to modulate my Comcast digital cable coax, as well.

Don't want to give up a channel 2-6, but will if I have to.

Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense. -Buddha

Give a monkey a brain and he'll swear he's the center of the universe. -Fishbone
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post #8 of 12 Old 12-21-2008, 10:18 PM
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Why dont you use the cable box coax output, It outputs at channel 3 and feed that in your system. You will have to get a channel 3 filter. This way you wont have to use a modulator.
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post #9 of 12 Old 12-24-2008, 05:05 PM
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I think a better solution is to put the modulator a little above the highest frequency your cable system is using rather than hassling with notch filters. Beware however that inexpensive modulators don't have good vestigial sideband suppression so you should go at least two channels above the highest cable channel to avoid interfering with it.
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post #10 of 12 Old 05-12-2011, 11:40 AM
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Originally Posted by zoreo View Post

I think a better solution is to put the modulator a little above the highest frequency your cable system is using rather than hassling with notch filters. Beware however that inexpensive modulators don't have good vestigial sideband suppression so you should go at least two channels above the highest cable channel to avoid interfering with it.

good advice you may also want to check to make sure your impedance levels are appropriate for the project too.
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post #11 of 12 Old 05-12-2011, 11:40 AM
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here's some sample rf filters that i have that might help you match them up to make sure they are correct http://www.oscilent.com/catalog/Cate...saw_filter.htm
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post #12 of 12 Old 05-12-2011, 03:46 PM
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Unless the OP has a spectrum analyzer or a friend at the cable company that can tell him the highest frequency being used it is still a guessing game.

He is probably safe above 900mhz.
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