The diplexers will mix or separate DSS and TV channel signals. Those signals are in completely different frequency ranges, so they will never get mixed. It's kind of a real world example of the paint that they show in cartoons, that paints a black and white checkerboard pattern on the floor right out of the can, and does not get mixed to gray.
And diplexers don't care which way the signals are going, so one can go into it while one goes out.
First, I assume that "satellite feed" means the signal from the LNB to the receiver, and "satellite signal" is the channel three or four output from the satellite receiver. If that is not so, ignore the following and send us an explanation of what you mean.
First, design what you want, ignoring that you only have one cable. Make up a drawing showing where the signals go. Here's the limitation -- design it so that two cables run next to one another -- a "satellite feed" cable runs (in your drawing) next to a "satellite signal" cable. Forget about the direction of travel of the signal. Then, convert this to the real world: everywhere that you have only one cable, use a diplexer to combine or separate the two signals.
Where I say "diplex in" below, I mean I mixed the DSS signal with a cable signal; "diplex out" means I separate them.
I have done this in a totally crazy situation in a client's home: The DSS signal was diplexed on the roof into cable A, was diplexed out on cable B, went around a splitter, was diplexed back in on cable C, then was diplexed out to go to the DSS receiver. Cable A had the DSS signal going down it with a cable signal coming up it, cable B was DSS signal only, used to run the DSS signal around the 8-way splitter, and cable C carried both DSS and cable signal away from the splitter and out to the TV and DSS receiver.
It worked flawlessly.
A good answer is easier with a clear question giving the make and model of everything. "The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
