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Downlink budget calculation


I'm trying to calculate how much gain (from the antenna and preamp) I
need for satellite reception.

We have the link budget equation Prx = (Ptx + Gtx) + Grx - Afs - Am,
where Prx is the received power (dBW), Ptx + Gtx is the EIRP (dBW), Grx
is the receive gain (dBi), Afs is free-space attenuation loss (dB), and
Am is miscellaneous loss (dB).  My receiver specifications state that
its sensitivity is "better than -15dBu for 12dB S+N:N".

Okay, a dBu is dB relative to one microvolt.  How does this relate to
Prx in dBW?  If I take that -15 dBu, and convert to volts, then
calculate power assuming 50 ohm impedance (V^2/50) and convert that to
dBW, is that the correct value to use to find Grx?

Thanks and 73 de Joel KC8DQH.

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