How can I get it?

"if the TX power amplifier delivers 1W to a 50Ω antenna, the peak to peak voltage swing is equal to 20V. The leakage to the receiver path is on the order of 30mVpp(=-26dBm)"

I think P=Vpp*Vpp/(2*R), then Vpp=10V ,not 20V. Am I right?
30mVpp=-26dBm? How can I get it? Thanks in advance!

for resistive load (linear) and sinusoidal waveform, equeation will be:
P = (Vrms)^2 / R
P = (Vpeak)^2 / (2 x R)
P = (Vp-p) ^2 /( 8 x R)

how can and get!

P(dBm) = 10 log (Pout/1mW)
Pout = (Vp-p)^2 / (8xR)
P(dBm) = 10 log (0.00225)
P(dBm) = 10 x (-2.647) = -26.47dBm ≈ -26dBm