general idea
Roughly speaking, the C-band is heterodyned down to the 950-1450 mhz range.
So, (C-band signal - 5150mhz LO = spectrum analyzer signal)
The receiver selects whether that's a vertical or horizontal transponder.
ie:
Galaxy 16 @ 99° West - transponder 15 Horizontal = 4000 mhz
so, 5150 - 4000 = 1150mhz
You'll find that 1150mhz signal on the "loop out" connector of your receiver.
Depending on the equipment, it may be known by a different name, but it's just a buffered copy of the signal from the LNB.
Under some circumstances, you could tap the signal between the LNB and receiver.
As to channel spacing, take a look at the Lyngsat listing above showing transponder frequencies.