What frequency can penetrate walls?

UHF radio waves propagate mainly by line of sight; they are blocked by hills and large buildings although the transmission through building walls is strong enough for indoor reception.

VHF has smaller frequencies which means interference with other radios is common. UHF, on the other hand, is an all-around better signal for long distance communication. UHF is better when using radios for indoor use like buildings or around cities .

Radio frequency is easier to generate and because of its large wavelength it can penetrate through walls and alike structures. Radio waves can have wavelength from 1 mm – 100,000 km and have frequency ranging from 3 Hz (Extremely Low Frequency) to 300 GHz (Extremely High Frequency).

Brick walls have to be unrealistically thick to be useful . Other materials, such as windows and drywall, are essentially fully transparent to radio waves. Reinforcing a concrete wall with steel rebar did not really improve the shielding, at least at the standard grid sizes.