AM, which operates at a lower frequency, has radio waves with larger wavelengths, meaning they travel farther but struggle to penetrate solid objects like buildings.
Aren’t low frequencies better at penetrating materials?
yes they are, you can detect lower bands pretty much everywhere. The problem is modulation: AM sucks balls when it comes to noise rejection. Some AM stations switch to digital encoding which uses the same band so good propagation + good audio quality within some range. After you get too far away signal just drops, if you’re willing to put up with higher noise level range of normal AM radio is basically global
Yes. But any metal in the building that’s smaller than the wavelength of the AM radio frequency which is quite long, will absorb the radio wave so it won’t penetrate the building
I think you mean that statement the other way around, and it’s not going to perfectly absorb even in that case unless you have a true faraday cage.
Buildings won’t perfectly absorb signals but it will attenuate the signals that pass through them.
The gaps In a faraday cage determine the maximum wavelength of the electromagnetic signal that can pass through. AM signals have very long wavelengths, and are more likely to get distorted
Any metal in a building will act to distort and absorb signals, the more metal, like rebar in concrete, the less signal can get through.
Examples:
Consider the ocean, ionic water, very difficult to get radio signals because there are so many dense charge carriers to absorb the radio waves.
Consider the earth: sending radio signals through the center of the earth is difficult because of all the metal, electron carriers in the earth itself.
Consider wifi in a modern concrete and rebar office building, one or two rooms over and the signal gets absorbed quite effectively.
I think I understand better where you’re coming from. I have a variety of homemade low frequency antennas, typically on the order of 20 meter wavelength, and I observe lower frequencies clearly get better reception inside buildings. Transmission tends to be more variable because I have an increasingly large near field zone that’s effectively impossible to clear. Indeed, my real world experience has always been the opposite. Lower frequencies appear to get through better, provided you can actually talk out. I usually prefer to modulate the H field because it’s orthogonal to household noise sources and after some distance away doesn’t couple to metal.
I’m not sure why this is. Perhaps buildings are different enough from Faraday cages? Lower frequencies diffract and bend around objects much much more effectively than high frequencies.
I have some RF design engineer friends and I’ll ask them why my experience is different.
wrong
it penetrates buildings just fine
