Choose a location clear of obstructions. Power up the system once more. Holding the boom by the rear and above your head, point the antenna towards the zenith, that is straight up. This will be the quiet sky. Listen to the noise level and make a mental note of the volume.
Headphones are useful here.
Now point the antenna at the ground. Now point the dish at the Sun. If it is shining, this is easy. If it is obscured by cloud, you will have to use your skill and judgment. Either way, the noise level should rise by about 1 db compared with the quiet sky.