I've been having a hard time understanding much of the discussion above, particularly, it sounds like some references to splitters are really referring to diplexers. However, relative to the use of splitters, I have been using splitters ever since I upgraded my analog system to digital about 13 years ago, and have had splitters in the system ever since, although the types of splitters have varied over time.
I have gone back and forth relative to whether splitters are better than using the passthru ports on receivers.
My original use of splitters, which is probably the same as 99% of people who upgraded a C/Ku analog BUD was first to slave a standalone DCII receiver, and later to slave a DVB receiver. Basically I split the line from each of the 2 LNBs, on leg going to may analog receiver, and the other leg going to my DCII receiver through a DC-block. When I wanted to also use a DVB receiver, I put the DVB receiver in place of the DCII receiver, and used the passthru to feed the DCII receiver, since my DCII receiver didn't have a passthru, and since I didn't want to split more than to 2 devices. Since this at first limited me to only C or Ku at the DVB receiver, I then got a 2x DiseqC switch (the simple A/B pulse type) to select either the line from the C or Ku splitter. This also worked fine, and the signal strength/quality at the end of the line on my DCII hardly changed at all from before. I then got PCI card receiver for my computer, so I inserted that between the DVB STB and the DCII receiver, again using the PCI receiver's passthru port. Again, I couldn't notice the difference in signal at the DCII receiver.
In short, I became an advocate of using passthrus because I intuitively believed that I'd lose half the signal with splitters, so I tried to avoid splitters whenever possible, and signal strength wise, I could observe this on my analog receiver, in that in splitting off the signal to the digital receivers, the signal strength dropped about in half, but it really didn't affect the quality of the analog picture much.
Upon adding even more receivers, I've at times extended to using even 3 passthrus before reaching the last receiver in the line.
HOWEVER, recently, I have come back to thinking that splitters are BETTER than passthrus in a lot of cases. The thing that was fooling me about passthrus is that I wasn't noticing any drop in signal when using a passthru, but that was apparently because many of these passthrus are amplified. So I was starting to see degradation in quality, even though the signal strength was as high as prior to the receiver with the passthru. Recently, I've gone from using the passthru to using a splitter prior to one of my DVB receivers, and I'm now able to lock a couple transponders that I was only able to lock before if I connected directly to the LNB.
Anyway, I started out using splitters, shifted partially away from splitters due to concerns about signal strength, then have gone back to splitters over concerns over signal quality. So there is definately a place for splitters in my system. I've always used them. However I have ALWAYS used them with DC blocks, and have NEVER allowed two receivers to have the possibility of sending DC voltage to each other.
Also, I have found very little difference between the cheap splitters that are used for TV, and only rated up to 1000MHz, and the more expensive splitters that are rated up thru 2000 MHz. There may be some small differences, but I've never noticed anything I couldn't receive using the cheap splitters that I could receive using the more expensive ones.
I also think that the concept of losing 3dB of signal when you use a splitter is not always the case. I think that it depends upon the impedance of the receivers you are using. I think that some of these receivers, even though they are using 70 ohm coax connections, are really higher impedance, and basically, the higher the impedance, the less effect they have on the original signal. Sort of like putting a 20,000 ohm VOM in a circuit will change the voltages, but putting a megohm VTVM or digital meter generally won't affect the voltages being read because they are drawing negligeable current. A lot of concepts regarding power loss in things like splitters is more applicable for transmitting than for receiving. For receiving S/N is more important then signal strength anyway, so splitters often don't affect your signal quality nearly as much as people suspect, since even if there are losses, the noise will also be reduced.
Anyway, just my take on splitters. I use them all the time.
And I have the task at hand: splitting a signal coming from my STB's Pass Through port btw 2 lines: one going to an Add-on card mounted inside the STB, another to one of my Sat Card PC tuners mounted inside a PC. I looked around for a high frequency splitter, and found several types, including non-power passing, DC power passing on one OUT port, and DC power passing on both OUT ports. I assume, they are dual-directional (or not?), i.e. DC is passed from IN to OUT splitter port(s), and in opposite direction (not blocked from OUT to IN).
