The signal from the sky thus attenuates massively before it reaches the ground. At other frequencies the ionosphere reflects the radiation back into space. To do effective radio observations, one must choose an frequency that will propagate through the atmosphere effectively. The problems optical observers have with light pollution are well known in some circles. Radio observers have the same problems.
Human activity generates a great deal of radio noise on a wide range of frequencies.
Some frequencies have been specifically set aside by international agreement for radio astronomy. Of course the reality is not always like that. Some human produced radio noise is very broadband and will disrupt observations at virtually any frequency. Yet even so, the resolution that a modest radio telescope can expect to achieve is much less than what a similarly modest optical telescope could obtain. Expensive Equipment Optical observing can be done with no equipment at all.