Will the quality of the picture from my UHF/VHF antenna or satellite dish be harmed by combining and then separating the two signals going down the same cable or is only the strength of the sat signal affected?
In my setup, I only have two coax connections; and I have a 811 and a 510 connected to the same tv. So, coax out1 goes to a diplexer, and from the diplexer to sat in and antenna in of the 811; coax out2 goes to the 510. To my eyes, I see no degradation in signal strength or picture quality. I even the swapped cables on the satellite inputs of each receiver and still saw no difference in picture quality.
If they are going to share a cable, use a diplexer! Yeah, it sounds silly, but some may think that regular signal splitters/combiners (like you would use for cable/antenna distribution) would work just fine. Diplexers handle the LNB power properly.
Last night I compared signal levels on OTA ATSC stations using a diplexed (via Terk BMS-58 multiswitch) and a direct run from the antenna/preamp to the receiver.
There was absolutely no difference in signal levels at the receiver. None. Fluctuations were identical. Peaks were identical. On every single ATSC station I could get -- even on those I see some signal but not enough to lock a picture.
There may very well be difference if we were dealing with NTSC tuners, but at least with ATSC, the modest loss in using diplexers makes no difference ot the receivers ability to tune the signal.
And at least one of my ATSC station is on the edge of watchability sometimes, and it remained quite watchable either way I wired the antenna.
I have 2 antennas ran to a combiner then the antenna cable into a diplexor with 1 line from the sat. I have another diplexor on where the cable comes out of the wall and 1 ran to 811 sat the other 811 ant. I have a second cale ran from dish to 510. Works great!