Diplexor Turns Strong OTA to Zip - Help ! - AVS Forum
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post #1 of 17 Old 11-03-2004, 02:34 PM - Thread Starter
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I have a CM 4221 antenna and a Winegard preamp 4700 in my attic and get a strong signal on all desired OTA channels when running a seperate independent external cable from the attic antenna to the TV.

However, when using a diplexor at both ends to use the existing cable in the walls, my signal goes from 80 plus down to only 19. My cable run is only about 30 feet. At the suggestion of a local antenna store, I have a diplexor with power pass on both UHF and Sat on the combining diplexor in the attic and have a diplexor with power pass only on the sat side when seperating the cable to the receiving end (antenna and Sat inputs) on the TV.

I am hoping to avoid running seperate cable as the TV is on an interior wall and will be difficult to run.

Is there a fix for this to allow use of the diplexors such as different diplexors, stronger preamp, better configuration ? Any help would be most appreciated !
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post #2 of 17 Old 11-03-2004, 03:23 PM
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What did you do with the preamp power supply? In the scenario described, it should be removed. In that case, the signal voltage from the satellite receiver is used to power the preamp. That means the preamp is running off 13VDC or 18VDC depending on the channel selected. The 4700 probably has a 24VDC power supply.

If that is the case, it would be better to use a single passthru diplexer at the top as well as the bottom. The 4700's power supply is then placed between the top diplexer and the preamp to provide full voltage.

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post #3 of 17 Old 11-03-2004, 04:47 PM - Thread Starter
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Thanks for the reply Greywolf. I did not use the power supply (but tried it with power also). I will get another single pass diplexor and try that along with the power supply.

Do you think that will solve it ?

From my reading I realize that some loss is expected with diplexing but this seems too drastic.
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post #4 of 17 Old 11-03-2004, 05:14 PM
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It's a step in troubleshooting. Another possibility is a bad diplexer.

Pat

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post #5 of 17 Old 11-03-2004, 05:36 PM
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GREYWOLF strikes again. Go get'em greywolf, the KING of ANTENNAS, DIPLEXORS and DIRECTV DISHES.
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post #6 of 17 Old 11-04-2004, 12:07 AM - Thread Starter
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OK, I tried the single pass thru diplexor at both ends along with connecting the power supply as you suggested. It seemed to slightly improve one channel but reduced the signal on another. I also tried a replacement diplexer at both ends to eliminate the bad diplexer theory but there was no change.

Any other ideas ?
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post #7 of 17 Old 11-04-2004, 05:33 AM
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Also check your cables and connectors paying attention to the center conductors, if you have a second person one of you flex and bend the cables near the ends (one at a time) and look for signal level changes. It could be as simple as that or if you have extra short cables try swapping them out.
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post #8 of 17 Old 11-04-2004, 08:21 AM - Thread Starter
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I will check all the cables. I do have some short cables from the diplexors.

I should note that disconnnecting the cable from the diplexor to the sat input on my receiver gives me a strong signal again. Does this tell us anything ? Are you saying to replace the short cables with long cables or just replace them as they may be bad ? I'll try playing with sat input cable first.
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post #9 of 17 Old 11-04-2004, 08:28 AM
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If the cables are all right, the diplexer loss, though small, may be crossing over the edge of good/bad signal. In that case, you can try, in order of signal improvement preference, getting the antenna outside, trying an 8 bay antenna like the 4228, getting a better preamp like a Channel Master 7775 (7777 to future proof against the time when a local station may go back to VHF) or Winegard AP-4800 (AP-8275).

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post #10 of 17 Old 11-04-2004, 10:13 AM
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Is the pre-amp powered or not?
If it isn't just remove it from the chain if it is you need to block the DC coming from the sat receiver (where it combines in your attic).
I previously mentioned checking and possibly replacing a cable, I used the term short, I was only referring to the cable between the diplexor and the STB. (actual length doesn't matter).
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post #11 of 17 Old 11-04-2004, 03:19 PM - Thread Starter
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The preamp is powered. If the diplexor only has power pass on the Sat side will this block the power as you suggest ?
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post #12 of 17 Old 11-05-2004, 08:02 AM
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I was reading last night and it seems that is case. I have Channel Master 4001 diplexers and they don't pass DC on the ANT side. I don't have any that do pass DC so I can't test this out.

Steve McClure
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post #13 of 17 Old 11-05-2004, 08:24 AM
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Do you own a dvm?
If so to prove it (DC on the OTA side) remove the OTA connection from diplexer and measure DC volts from center pin to shield.
How is the signal without the pre-amp is it watchable at all, if so remove it and connect antenna directly and look at ota signal with and without the sat side connected look for any differences.
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post #14 of 17 Old 11-05-2004, 12:17 PM
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I would disagree that diplexers offer only a small loss. In my experience, certain models can cut a significant amount of signal.

As inconvenient as it can be to run the extra line, you may be best off running a direct line from the antenna to the digital receiver. This should also help you in future troubleshooting.

Also increased amplification of the OTA signal can cause you to lose your satellite channels. (when the signal is diplexed)

When it comes to digital reception, there are many links in the chain of failure, and any extra accessories on the line such as splitters, diplexers, junctions and even amplifiers can introduce interference on the line or attenuate signal.

The most simplistic connections are usually the most successful. i.e. non-amplified UHF antennas, with short cable runs, directly connected to the digital receiver.
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post #15 of 17 Old 11-05-2004, 04:35 PM
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I know this may not be a solution, but I went through all the troubles you are talking about. I finally wound up with a preamp that worked with my diplexer and antenna. I got it from Lowe's. It was Channelmaster 3041. It seemed to work very well with the voltage from my RCA DirecTV receiver. The good thing was the Lowe's told me if it didn't solve my problem to just return it!

I used the following diagram from 18inch.com to help me with the wiring:
http://www.king-cart.com/store/18inch/PwrAntDipDraw.jpg
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post #16 of 17 Old 11-06-2004, 07:04 PM - Thread Starter
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SUCCESS AT LAST !!

Well after experienting with many configurations (diplex single pass, diplex double pass, amp, no amp, etc) I finally got a stronger antenna signal by using the double pass diplexer at the TV end and the single pass diplexer at the antenna but then my Sat signal was weak.

I finally gave up and decided to run an extra line. It turned out that it was really quite easy. There was a lot of extra cable in the attic so I was able to simply tape the extra line to one of the Sat lines in the attic and then I simply pulled both lines together all the way down to my TV on the first floor (2 story house).

I am now getting a very strong signal on all desired channels. Needless to say I am very very happy to have my pristine HD after a lot of hard work. Oh yeah, the antenna situation was another fiasco by itself which preceded this whole diplexer issue.

Thanks again everyone for all of your input and ideas.
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post #17 of 17 Old 11-06-2004, 07:10 PM
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A dual pass diplexer at the TV end allows DC from Sat connector to get to the Ant connector. This should never be done. It sounds like the single pass diplexers tried at that area were not working properly.

Pat

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