1) is the passive combiner with frontal connection usable independently of the active part without any secondary problem?
It's a completely separate, passive, circuit. Simply in the same rack frame for convenience.
2) The same passive combiner is reversable? (i mean could be used as a passive splitter? DC block?)
Yes, being passive it's bi-directional. This circuit will not pass DC,
2) Specs say max input level is +24dBm each channel. What about output signal level? I mean: ch1 +17dBm and ch2 +14dBm remain exactly the same in the combined output?
This is a unity gain stage; meaning whatever RF level is input for a given frequency, that's the level that will be at the output, independent of other input levels, circuit variances of +/- 2dB notwithstanding.
3) If not 8ch are in use, using not adiacent ch can provide any vantage in isolation and maybe IMD?
Yes, if there are less than 8 feeds, not using adjacent ports is recommended to reduce potention IM. Adjacent ports with active inputs should have the greatest frequency separation possible. If you take the input frequencies in ascending value, connect to combiner ports 1, 5, 3, 7, 2, 6, 4, 8.
4) providing +17dBm (50mW) every input, what is the 3th, 5th,7th order IMD level in the output?
I seem to recall the unit is rated for -70dBc (though it's not published). Thus the 2TX 3rd IM would be at -53dBm, 5th at about -59dBm, 7th at about -68dBm.
as usually, sorry for my bad english
No worse than some of the native English speakers . . . on both sides of the pond, and in both hemispheres.
