For the 22 GHz water maser (H₂O) line, the laboratory rest frequency is approximately:
22.23508 GHz = 22,235.08 MHz
Astronomical maser emission is Doppler shifted by the motion of the source and Earth. A useful conversion at 22.235 GHz is:
1 km/s ≈ 74.2 kHz
So the approximate received frequencies are:
Radial velocity Approx. frequency
−200 km/s 22.2499 GHz
−100 km/s 22.2425 GHz
−50 km/s 22.2388 GHz
0 km/s 22.2351 GHz
+50 km/s 22.2314 GHz
+100 km/s 22.2277 GHz
+200 km/s 22.2203 GHz
For Galactic star-forming-region water masers, a receiver covering roughly 22.220–22.250 GHz gives a generous ±200 km/s window. Many well-known sources occupy a much narrower range.
For your observations of sources such as W49, W3(OH), Orion KL, W51, etc., I can give you the actual expected frequency range for each source, including the LSR velocity range and the frequency you should tune your SDR to with your Norsat 9000LDF.