Diplexing question

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New Member
Aug 9, 2011
Denver, CO
Hello everyone,

I'm brand new to this forum and hope to get your thoughts on a possible configuration.

I currently have DirecTV service with the Slimline dish and the SWiM and DECA. The configuration is as follows:

Dish (1 coax line) -- 3-way splitter (outside) -- SWiM (on one of the outlets) -- DECA. Only 2 of the 3 outlets have a receiver, the third outlet only has the SWiM and DECA hooked up. The DECA is hooked up to my internet router, which is connected to DSL. So far so good, everything works great.

I now want to get cable internet for various reasons. Since I can't run any new wires, I was thinking about diplexing the cable internet signal as follows:

Dish (1 coax line) -- 3-way splitter (outside). 2 of the 3 coax lines will run directly to the two receivers that I have, one of them having the SWiM in between. The third coax line from the splitter will run into a diplexer, with the second feed being Comcast cable internet. At the third outlet, another diplexer will separate the signals again. The non-satellite output will run into my cable modem, which is connected to an internet router. The DECA will be connected to the internet router and the coax will run into the sat-output of the diplexer and supply the two receivers with an internet connection.

At least that's my theory. My question is: could this configuration really work and if so, what kind of diplexers will I need ?

Thanks in advance, and please let me know if you need additional information.



SatelliteGuys Pro
Sep 17, 2010
You can't diplex anything onto a SWM system. There are no diplexers that are compatible with the frequency set (SWM uses a 2MHz control frequency, which must be passed on the SAT ports, I have never seen a diplexer that goes below 800MHz on the SAT port), and also the Ka Low (B band) signals used in HD are in the same range as the cable signals (250-750MHz). So not only will the diplexers strip the B band signals off the line and route them to the UHF port, but those signals will interfere with your cable modem's downlink frequencies.

There is no way around it, you will have to run a new cable for your modem. What is the issue that you can't run it?


SatelliteGuys Pro
Dec 2, 2008
On Your Roof!
yes you can diplex into swm but in limited ways with 9501 diplexer. Since you have MVR or Deca for VOD you cant diplex onto any of those lines as the deca uses the same freq but other ways around it .

If you could make a crude layout in MS paint we might have an option that would work

Ex pos.JPG
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SatelliteGuys Pro
Pub Member / Supporter
Apr 12, 2006
coloradoan - it might seem you have received confusing answers but both posters are giving you relevant information.
First, my recommendation would be to stay away from diplexing completely. There are so many problems you might run into and they will be very difficult to diagnose and fix.
Second, the technical stuff. As you can see from the posts there are a number of signals in the SWM system and in WHDVR that the sat cables carry, and if the diplexers you use don't support those signals correctly things won't work properly. Also, if the signals from the cable internet system overlap any of the DirecTV signals it won't work either.
Jerseymatt's comment about diplexers and the SWM control signals are important but not 100% correct. It is true that many diplexers won't pass the SWM control signals correctly, but not all. There are a few diplexers that DO pass the control signal, even though the spec indicates they might not. In fact, DirecTV's original stand-alone SWM multiswitches had built-in diplexing for off-air signals, and for a few years I had a perfectly good diplexing system for off-air signals using SWM. However, I had to abandon that when I installed the WHDVR system because the off-air signals and the WHDVR signals (from the DECA devices) overlapped.
The next problem is the signals that are carried on the cable internet. Most cable internet cables carry three different sets of signals. There are the signals from the internet and the signals between your cable modem and the cable company. different cable systems use different frequency bands, for example your signals from the internet might be at around 750Mhz and the control signals back from the modem might be at, say, 54Mhz, but mine might use different frequencies. You may also have cable TV signals on the cable, because even though you don't subscribe to cable TV, that does not mean the cable company has filtered them out. Without knowing what frequencies your cable modem uses for both the upstream and downstream paths, it's impossible to draw up a frequency usage "map" for your particular system, so it's difficult to predict whether or not you could set up a diplexing system that will work. SWM, WHDVR, cable modems and diplexers don't play well together.
Hence my recommendation - don't do it!
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