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Guest Message by DevFuse

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Diplexer's revisited


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5 replies to this topic

#1 OFFLINE   Chris Blount

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Posted 01 April 2002 - 07:10 AM

Well, here we go again with yet another diplexor discussion. The reason why i'm bringing this up is because one of my local broadcasters just recently went on the air with their digital signal. First for the people that don't know. Diplexors are used to combine the input signal from a satellite dish and an input from an over-the-air (OTA) antenna. Both are carried into the house on one cable. Then inside there is another diplexor that splits the two signals back out so one can go to the satellite receiver and the other can go to the TV or HDTV decoder to receive OTA broadcasts. This eliminates the need to run a separate cable for OTA.

My setup is a standard Dish 300 pointed at 61.5, outdoor medium range antenna, 2 Radio Shack diplexors (inside & outside) and a Model 6000 receiver.

First I hooked up two separate cables. One for OTA and the other for dish. No diplexors.

Signal strenth on the dish was 98.
Signal strength on OTA digital was 83%

Then I hooked in the diplexors and got rid of the extra cable.

Signal strength on the dish was still 98.
Signal strength on OTA digital was 80% (only a 3% drop)

Other analog channels on OTA before and after look exactly the same.

In my opinion diplexors work great in this kind of setup. The OTA digital signal showed no pixelation problems or other anomolies. The OTA and satellite channels work flawlessly.

Despite what some people would say, diplexors can and do work for certain types of setups. Yes, running a separate cable is always the best but when that's not feasable, diplexors should at least be tried. IMHO

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#2 OFFLINE   Mark Lamutt

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Posted 01 April 2002 - 09:49 AM

Chris, do you need the outdoor antenna for your HD reception? I ask because I originally went with the outdoor antenna and was going to use diplexors, but on a whim I picked up the radio shack double bow tie antenna (part #15-623), set it on top of my tv in my basement, hooked it directly to the 6000 and ended up with significantly better signal strength than I had with the outdoor antenna. Something to consider...
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#3 OFFLINE   MarkA

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Posted 01 April 2002 - 07:56 PM

Mark L, your outdoor antenna had a cabling problem or wasn't connected correctly. Under no circumstances should a bow-tie give a better signal than a properly setup outdoor antenna. One question - is the antenna you bought at Radio Shack amplified, and your outdoor antenna not? If so, get a nice amplifier for your outdoor antenna and be amazed! As for the diplexers. Diplexers do not work very often. I have NEVER seen diplexers that didn't destroy the analog OTA picture (and I've seen several diplexer setups).

#4 OFFLINE   Mark Lamutt

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Posted 01 April 2002 - 10:17 PM

Mark, normally I would agree wit you, but I'm in a bit of an odd situation here in Denver. We have 3 stations broadcasting very low power digitally- ie 7 kilowats vs 1-5 megawatts. I had the big rooftop antenna for a couple of days running to the 6000 with 50' of good quality RG-6 cable. No amplifiers and no diplexors. I was pointing right at the trasmitters that are 4 miles away LOS, and I was getting enough signal to lock on, but not much more. Then I tried the double bow tie, and am now getting about 20 points more on my signal strength with it. Everything was hooked up correctly, I just have a sweet spot in my basement where the bowtie works (and it's not amplified - check out the model on the RS website, it's 15-623).

If I were trying to pick up normal powered signals, then I would think that the larger antenna would be better, just not in this case for me.
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#5 OFFLINE   MarkA

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Posted 01 April 2002 - 11:14 PM

Weird. Very weird. I might get an outdoor antenna one day. I'm using a little Philips antenna connected to my computer for locals (no locals on my TV. The computer let's me PVR them:) and it has a RF remote). I live in a Grade A (at worst) or city grade for all signals, and while it's okay, I do get a little snow.

#6 OFFLINE   pctech

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Posted 07 December 2003 - 03:22 PM

I use diplexers all the time as a SBCA certified dish installer (DishNetwork & DirecTV). I have encountered only one situation where the diplexers did not work.

The customer had two TVs with cable to the home run and wanted TV1 to mirror to a third TV that did not have cable to the home run. TV2 and TV3 had cable in the attic.

I installed 301 receivers to TV1 and TV2. I diplexed the coax output of receiver 1 to the incoming dish line, diplexed the combined signal at the home run to split the signal, recombined the OTA signal into the dish line for receiver 2, diplexed the combined signal in the attic and sent the OTA signal to the mirror.

Everything worked great. For about a week. The customer called and said they had lost signal on TV2. I found the SAT IN connector on receiver two was not working so replaced the receiver. A week later the same problem occured. I reconfigured the system so that TV3 mirrored TV2 instead of TV1 using one diplexer to combine the signals to the attic and a second to split the OTA signal off to the TV3 line. This is the normal diplexer configuration. No more problems.

I have seen no discussion pro or con of diplexing up on one dish line and rediplexing down on another dish line. Apparently, this should not be done as the combined voltage from the two receivers will burn out the SAT IN connection.




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