It is - virtually - impossible without phase locked LNBs to combine signals from more than one dish
What are you trying to receive on your system and how far short of the signal are you with one dish ?
I think the OP wants to send the output from a single LNB to two receivers.
As the splitters operate in the intermediate frequency band after the first downconversion, I don't think there should be anything special about C-Band.
The passive splitters I have used for Ku do take away up to 6 dB of signal strength, but they normally do not take any of the quality.
The impact is ususally only felt if the gain circuitry in the reciever does not provide same effeciency across the gain.
In general, I would concurr with PaulR: An inline amplifier before a passive splitter may be what you need.
Can you post some more details:
- what dish, feedhorn etc do you have?
- what sats and transponders are you aiming at?
- what receivers are you using?