[amsat-bb] Calculating link budgets with linear satellites

I've recently been toying with spreadsheets to estimate antenna requirements for some of the upcoming satellites. I'm not sure, however, how I should integrate the downlink power of a linear bird over its bandpass.

Take for instance Delfi C3. It is said to have a 400mW downlink in a 40kHz bandpass. Does this mean that a solitary CW signal would be 400mW, two such signals (both with equal uplink power) would produce a 200mW downlink, etc.? In calculating power and pathloss using the simple addition and subtraction of dBm, what starting value is it recommended that I use in this case?

73, Bruce VE9QRP