Help with diplexing

[jdiehl]

Quick rundown on what I'm doing.... I have two HDTV's, a triple LNB DirecTV oval dish (phase III I think, purchased last summer from CC), just 4 lines coming from the dish (4 receivers, 2 of them are HD), and I don't see a multiswitch of any kind... I think it's sorta built into them now, right?.

Anyway, I'm wanting to feed my OTA antenna to both HDTV's, which I've successfully done (both are getting the OTA signal just fine). I used a standard VHF/UHF radio shack splitter to get 2 feeds from my antenna. The antenna is in my attic and located on the other side of the wall from my 1st receiver. For that receiver, I just ran it straight from the splitter to my receiver. No problems there, no diplexing needed.

For HD receiver #2, which is located about 40ft away in another room, and on a wall that can not be fished (to run a straight line from the antenna), I found the direcTV coax supplying that receiver and added a diplexer there. I simply cut the line, ran about 40ft of RG6 from my split OTA antenna, and screwed them into the dixplexer (RCA VHD920).

At HD receiver #2, I took the feed from the wall, ran it into an identical diplexer, and took the OTA and D* feeds into my HD receiver.

Here's the problem. The OTA signals are coming through just fine on this 2nd receiver, but I get 0% signal for DirecTV. I don't understand what I did wrong? The way I understand it, I have it connected properly. I essentially cut the line in the attic about 15ft away from where it goes down to the room with the 2nd HD receiver, and added the diplexer there. And then on the other side of the wall downstairs, I used the other diplexer. I double checked both diplexers to make sure I had the SAT and OTA jacks correct and not switch (OTA HD works perfectly anyway, so I know that wasn't it) but it seems to not want to pass the DirecTV signal at all.

Can anyone help me out here? I'm desperate and want to get this done ASAP before my attic gets hotter than hell. I thought at first it was a bad diplexer, so I swapped out both and got the same result (OTA coming through, but no D* signal)?

Is there a different type of diplexer I should be using that is made for the triple LNB dish? All I want to do is combine the OTA and D* for about 15-20ft of the RG6 run since I can't fish down this one wall.

 

[jdiehl]

Okay, in reading old threads here, could this have something to do with DC going to the OTA antenna and causing power/signal loss to the dish?

To test, I unscrewed the OTA coax feed from the diplexer in the attic, but my satellite signal did not return. Also, both types of diplexers I tried showed "DC Pass" on the SAT side, but not the OTA side, so I think I have the proper ones (my OTA antenna is not powered, so the DC should be blocked on the OTA side).

Still lost while adding a pair of diplexers on one coax feed to one single receiver would cause a complete loss of signal.

 

[jwtracey]

Sounds like you have it hooked up correctly. I essentially did the same thing with one HD rcvr and a powered OTA antenna although I needed to move the DC power supply up to the attic since both the DTV rcvr and the power supply were trying to put different DC voltages on the same coax. Check out this thread:
http://www.tivocommunity.com/tivo-vb/archive/index.php/t-183413.html
Good luck!

 

[jdiehl]

Out of frustration, I went back in the attic and used a simple F-type coax coupler to reattach the coax that I had cut.. thinking, okay, let's start at square one and make sure I can just get the sat. signal here... no antenna, no splitters, diplexers, just a straight shot from the dish as it's been since I had it installed last August. I did that, and still no signal.

So, I confirmed that I was connecting it properly and that my diplexers are working fine. I ran a long run of coax from one room to the family room where I'm trying to feed this, and hooked up a 2ft section of cable with diplexers at either end. Everything worked perfectly.... another confirmation that it's the coax up the attic that is causing the problem.

So, apparently when I was in the attic and cut the coax feeding this location, the half that leads back to the dish got screwed up in some way. I went up and recut that half and put a new connector on it, still nothing. The cable from that point down the room works fine (I know this since it passes OTA just fine, so no loose connections there)... but what is puzzling is that I didn't tug on anything. Just snip, strip, and crimp... took all of 90 seconds earlier today, and I'm not sure how that piece of coax running back to the dish is no longer carrying a signal. It's new construction, the house is only 10 months old. Could something be wrong with one of the LNB's (my other 3 receivers are working fine though). Perhaps the built-in multiswitch? I'm at a loss as to how to diagnose this issue (at least I know it's not the diplexers now).

 

[jdiehl]

It took me all day, but I've isolated the problem. It wasn't the leg of cable going back to the dish, it's the section of cable going down the wall into my family room (where I'm trying to send both signals). I tested it by running about 20ft of new coax from where I put the diplexer, down through my attic access (into a closet) and hooked up the other diplexer and a small kitchen TV there. It all works fine (OTA and D* signals loud and clear).

When I try the exact same thing in the family room where I'm trying to get both signals, I get no signal on the sat. What's odd (and caused much frustration today) is that the OTA signal comes through just fine, but no sat. signal at all. Really weird, but at least I've isolated the problem (the ~15ft of coax from where I added the diplexer, down the wall, and into my family room).

The bigger problem here is that I can't really drop new coax to that location, which is why I'm using diplexers for OTA in the first place. I can't understand why this 15ft of coax would pass the OTA signal just fine, but no sat signal. This morning, before I spliced the line with the diplexers, it send my sat signal through perfectly (95+% signals). Coax is pretty fragile if you bend it too much, but I didn't really tug on it this morning... I just cut into it with side cutters, stripped it with a coax stripping tool, pushed on F type connectors, and crimped. No biggy, I've done it 100's of times.

Is there a way this short run of coax could be damaged so that the high frequency signal from DirecTV is not coming through, but the low frequency signal from my OTA antenna still can get through? It's not completely damaged, obviously, since I can get OTA through there, but 0% sat signal.

 

[uboatcmdr]

It took me all day, but I've isolated the problem. It wasn't the leg of cable going back to the dish, it's the section of cable going down the wall into my family room (where I'm trying to send both signals). I tested it by running about 20ft of new coax from where I put the diplexer, down through my attic access (into a closet) and hooked up the other diplexer and a small kitchen TV there. It all works fine (OTA and D* signals loud and clear).

When I try the exact same thing in the family room where I'm trying to get both signals, I get no signal on the sat. What's odd (and caused much frustration today) is that the OTA signal comes through just fine, but no sat. signal at all. Really weird, but at least I've isolated the problem (the ~15ft of coax from where I added the diplexer, down the wall, and into my family room).

The bigger problem here is that I can't really drop new coax to that location, which is why I'm using diplexers for OTA in the first place. I can't understand why this 15ft of coax would pass the OTA signal just fine, but no sat signal. This morning, before I spliced the line with the diplexers, it send my sat signal through perfectly (95+% signals). Coax is pretty fragile if you bend it too much, but I didn't really tug on it this morning... I just cut into it with side cutters, stripped it with a coax stripping tool, pushed on F type connectors, and crimped. No biggy, I've done it 100's of times.

Is there a way this short run of coax could be damaged so that the high frequency signal from DirecTV is not coming through, but the low frequency signal from my OTA antenna still can get through? It's not completely damaged, obviously, since I can get OTA through there, but 0% sat signal.

Check you connector (the one you put on the end after cutting the line) to be sure that one the tiny outer wires is not wrapped around the bigger center stinger wire. That will cause the powered sat signal to ground out while allowing the unpowered OTA signal to pass. You'd be surprised at how easy it is for that to happen (and miss), and how much it can muck things up.

 

[jdiehl]

Ding ding ding. We have a winner. While you were responding, I went back up there and clipped off the connecter I had crimped for the drop and put a new one on. Everything works perfectly now, thank God. I never knew how important it was to get that shielding away from the copper just perfectly.

 

[uboatcmdr]

Great! Glad to hear you got the problem solved. I know how wiring problems can really bug you. I'm an installer and I sometimes have bad dreams at night about wiring problems. Trying to work out wiring problems in your sleep is worse than those dreams I had as a teenager after playing Nintendo for too many hours. Gives me the cold sweats.

 

[jdiehl]

Yeah. What made it worse, and basically wasted my whole day, is that I thought I had isolated the problem to either the diplexers or section of coax going back to the dish because the OTA was coming through fine. If I had just redone that one connector right away, I would have been done in 5 min.

 

[asousa]

my installer is coming tomorrow and I have already have the cable run to my living room. Will he have diplexer's on him so I can keep my OTA antenna in the attic....or is this something I am going to need to add later?

Thanks

 

[uboatcmdr]

my installer is coming tomorrow and I have already have the cable run to my living room. Will he have diplexer's on him so I can keep my OTA antenna in the attic....or is this something I am going to need to add later?

Thanks

Your installer should have them (if he does expect to be charged extra for them, my company charges $7 each for the little buggers). If he doesn't have any you can try to get them off eBay (prices vary quite a bit there, but still probably cheaper than Radio Shack).
If at all possible don't use diplexers, they can reduce your signal strength a little. Ask how much is the wall fish charge as opposed to the price of the diplexers (you'll need two), if the wall fish isn't much more go for it (two wires are always better than one).