Testing antenna aimed at cold sky vs hot ground - can this be conducted in daytime or must it be done at night?

[Andrew Thornett]

Thanks to Alex for help answering this query, which I have often wondered about, and the answer to which might be of interest to others.

Andy

QUESTION:
Testing antenna aimed at cold sky vs hot ground - can this be conducted in daytime or must it be done at night i.e. does sunshine or even sun behind cloudy skies ruin the sky or ground temperature difference?

ANSWER:
Daytime, Nighttime Sunny or Clouds, it does not matter.

The temperature of the Ground does change, and that can be factored into the equation, if you really want to do so. However, that is a small fraction of the number = just do it whenever it is convenient.

[Marko Cebokli]

With a high gain antenna, don't point at the Sun. When cloudy, you can point it there without knowing...

The solution is, just keep watching the noise level, and point the antenna around the sky, looking for the direction with the lowest noise.

Marko Cebokli

30.12.2025 16:32, je 'Andrew Thornett' via Society of Amateur Radio Astronomers napisal

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[Alex P]

Use an SDR and select a non H-Line for Earth&Sky

[b alex pettit jr]

Any typically point @ Zenith for the Cold-Sky reading to minimize side lobe ground noise reception