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Guest Message by DevFuse

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Confusion over backfeeding


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24 replies to this topic

#1 OFFLINE   myvet

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Posted 10 December 2008 - 04:00 PM

I have 2 Direct tv DVRs (one in Bedroom and one in Living room - both are standard TV and 3 or 4 years old). I have 2 cables running to each unit. I have a dual LNB going to a multiswitch, then it feeds the 4 cables (2 to each unit). No problem. However - now I would like to watch programs on a TV on my Patio, in my garage, etc. I tried installing diplexers to run the signal back on top of the sat feed and out through the existing cables to the TVs , and I can get both signals (channel 3 and 4) on the other TVs - but the picture is bad. It looks like interference of some kind. I tried a signal booster, it did not help at all - if anything it made it worse.

Can someone help - maybe with an idea or a diagram of how I can accomplish this. Thanks

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#2 OFFLINE   kevinm34232

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Posted 10 December 2008 - 04:06 PM

Ive got a good diagram at the shop I will post it tomorrow if you haven't figured it out yet.

#3 OFFLINE   myvet

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Posted 10 December 2008 - 04:27 PM

Thank you - I would appreciate it:)

#4 OFFLINE   doctor j

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Posted 10 December 2008 - 04:34 PM

If you are trying to get both channel 3 and channel 4 (one from each box) at the same time on the same cables then you will get terrible interference one with another.
Higher grade modulators that can separate the channels a bit would be what you need.
Give a bit more info about set top boxes and what signals you are trying to distribute.

Doctor j

MFH-2 System : 2 Major Viewing Areas. 2 x HR20-700's & H21 in each area via E2/SWM-8. Hardwire gigabit switch to 30 mb/sec internet.


#5 OFFLINE   myvet

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Posted 10 December 2008 - 05:11 PM

The "boxes" are a DTV Tivo (DVR80) unit in the bedroom and a DVR R15-500 in the living room. My goal is to get both signals to all the TVs (so I can use PIP on the Living room during football). But - it is most important that I get the livingroom R15 to all the other TVs (including the bedroom) as that is the one I use to record most programs I want to watch. My wife uses the one in the bedroom to record her stuff. I enjoy watching taped programs as I am going to sleep. Also, The weather here is great this time of the year (sorry to all you who are not in Arizona), and we enjoy movies while sitting outside around the firepit. We have HBO we tape movies from - and would like to watch them outside instead of having to rent DVDs.

Hope this info helps.

#6 OFFLINE   doctor j

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Posted 10 December 2008 - 06:38 PM

As in my 1st post!
If you are outputing the coax of DVR80 on channel 3 and the coax of R15 on channel 4 (or vice-versa)and trying to use both, the interference (channel cross talk) will be too great.

Have you tried one or the other?

What you want to do can be done but you need separate AV modulators that can adjust the channel output and get them 4 or more channels apart.

Doctor j

MFH-2 System : 2 Major Viewing Areas. 2 x HR20-700's & H21 in each area via E2/SWM-8. Hardwire gigabit switch to 30 mb/sec internet.


#7 OFFLINE   doctor j

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Posted 10 December 2008 - 06:41 PM

Try this tutorial:

http://www.hometech....arn/video1.html

More info here:

https://www.smarthom...Common_Problems

Doctor j

MFH-2 System : 2 Major Viewing Areas. 2 x HR20-700's & H21 in each area via E2/SWM-8. Hardwire gigabit switch to 30 mb/sec internet.


#8 OFFLINE   spartanstew

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Posted 10 December 2008 - 06:52 PM

Can you run more lines to your living room location?

I'm sure Directv can't wait to get their hands on your unit.

 
Directv customer since 2000

#9 OFFLINE   myvet

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Posted 10 December 2008 - 06:59 PM

I can NOT run any lines to my living room - if I want to stay married. I have made that suggestion to my wife, and lets say the answer was "no".

That - unfortunately - is why I am here........................

#10 OFFLINE   spartanstew

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Posted 10 December 2008 - 07:01 PM

Bummer, I had the perfect solution for you.

I'm sure Directv can't wait to get their hands on your unit.

 
Directv customer since 2000

#11 OFFLINE   myvet

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Posted 10 December 2008 - 07:05 PM

Doctor J,

I have tried completely disconnecting the bedroom DRV, and still the picture quality from my living room DVR was still bad. Pretty much the same, maybe a little better than with both hooked up, but not good enough to enjoy a movie. The picture is a little snowy but has static vertical lines that move across the screen about 1" apart from eachother. That is why I thought I may have done something wrong and was seeing if anyone had a diagram or anything that may help.

#12 OFFLINE   MikeW

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Posted 10 December 2008 - 07:10 PM

You talk about having two different sources. I assume the sources are in different locations in your home. How are you combining those signals?

#13 OFFLINE   myvet

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Posted 10 December 2008 - 07:21 PM

I have the sat feeds on both sets of lines (2 to each receiver), then I use a diplexer to backfeed the RF output of each receiver back up, then undiplex and take off the RF feed and dirtibute them to all the TV's thru the pre-wiring in the house.

#14 OFFLINE   veryoldschool

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Posted 10 December 2008 - 07:29 PM

I have the sat feeds on both sets of lines (2 to each receiver), then I use a diplexer to backfeed the RF output of each receiver back up, then undiplex and take off the RF feed and dirtibute them to all the TV's thru the pre-wiring in the house.

I hope you're not trying to send this "backfeed" through your multi-switch. :eek2:
A.K.A VOS

#15 OFFLINE   MikeW

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Posted 10 December 2008 - 07:31 PM

Theoretically, you have two feeds coming back before it gets distributed. How are you combining those two feeds?

Where in AZ are you? I'm in SE Tucson and have a UHF Modulator that I'm no longer using. It's a Radio Shack unit, but it does the job. I currently use one to send a feed from my master bedroom back to my home office. I'm not much into shipping, but you're welcome to pick it up (for free). This would, at least, seperate the two channels for you.

#16 OFFLINE   myvet

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Posted 10 December 2008 - 07:43 PM

Thank you Mike - that is a great offer. I'm in Lake Havasu City, so picking it up would not work. I can go to radioshack and pick one up if you think that will fix the issue, but like I said, even with the DR in my bedroom offline, I still get a bad picture.

I combine the 2 signals using an old Tru-Spec combiner that blocks channel 3 from the one feed and combines the 2 signals.

And no, they are no going back thru the multiswitch.

Seems to me there should be a way to do this, but I feel like I am looking in the forest thru the trees, and am unable to grasp it.

#17 OFFLINE   doctor j

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Posted 10 December 2008 - 08:59 PM

Tru-Spec Combiner:

http://www.hometech....o/combiner.html

Only comment is that RF amplifier may be needed.
Question would be where?
Diplexer in/ diplexer out/ Truspec combiner/splitter to "other" TV's may leave you only 1/16th of original signal.

An exact diagram (or as close as feasible) may allow other suggestions.

Doctor j

MFH-2 System : 2 Major Viewing Areas. 2 x HR20-700's & H21 in each area via E2/SWM-8. Hardwire gigabit switch to 30 mb/sec internet.


#18 OFFLINE   doctor j

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Posted 10 December 2008 - 09:05 PM

I have the sat feeds on both sets of lines (2 to each receiver), then I use a diplexer to backfeed the RF output of each receiver back up, then undiplex and take off the RF feed and dirtibute them to all the TV's thru the pre-wiring in the house.


Does that include wiring back to BR and Den.
How many splits.
How long are the cable runs.
All of that suggests RF amlpification prior to reinjection into diplexer may help.

Doctor j

MFH-2 System : 2 Major Viewing Areas. 2 x HR20-700's & H21 in each area via E2/SWM-8. Hardwire gigabit switch to 30 mb/sec internet.


#19 OFFLINE   BattleZone

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Posted 10 December 2008 - 09:33 PM

Ok, so after reading the whole thread, I know exactly what the OP is trying to do, and why it isn't working.

The modulators in the DirecTV boxes don't output a very strong signal; they are designed to be directly hooked to the TV with a short cable, so if the output was too strong, there would be problems.

Everything you add to the signal chain reduces the signal: barrels, splitters, and especially diplexers. Many diplexers have HUGE amounts of signal loss. Plus there is some additional loss over the length of the cable.

This part could be overcome by adding a small (+10 db) amp to the RF output signal BEFORE diplexing.

If you are trying to get both channel 3 and channel 4 (one from each box) at the same time on the same cables then you will get terrible interference one with another.


The next problem is exactly what Doctor J quoted above: the mods that are in the DirecTV boxes aren't very high-end; a cheapie mod for a cable system is over $100, and more advanced ones can be over $1000. The point is that the mods in the DirecTV boxes will bleed over to the adjacent channels, so if the mod is outputting on Channel 3, you're going to have bleed-over on Channels 2 and 4.

Since your only options with the built-in mods are 3 and 4, you are simply never going to be able to use the internal mods AND combine the signals; they'll bleed over each other no matter what.

What you *could* do is keep the feeds separate, and dedicate one backfeed to one TV, and the second backfeed to a different TV.

The other alternative would be to purchase external AGILE modulators (AGILE = can be placed on any RF channel in a given range) and set them a couple of channels apart. You can probably find some that also increase the RF output strength by a good amount that will overcome the insertion loss of your diplexers, splitters, and cable runs.

But in the end, you're spending a lot of money to move SD signals around, and sooner or later (and probably sooner than you believe), you'll want HD signals instead. Think long and hard before you spend the money for RF distribution, and see if you wouldn't be better off with another receiver.

#20 OFFLINE   MikeW

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Posted 10 December 2008 - 10:34 PM

A while back, someone pointed me to this. I was thinking about getting it so I could get stereo sound. It's about the same price point as the Radio Shack device.

http://www.fadfusion...ber=20161200058




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