this post was submitted on 03 Jun 2024
167 points (98.8% liked)
Technology
59534 readers
3195 users here now
This is a most excellent place for technology news and articles.
Our Rules
- Follow the lemmy.world rules.
- Only tech related content.
- Be excellent to each another!
- Mod approved content bots can post up to 10 articles per day.
- Threads asking for personal tech support may be deleted.
- Politics threads may be removed.
- No memes allowed as posts, OK to post as comments.
- Only approved bots from the list below, to ask if your bot can be added please contact us.
- Check for duplicates before posting, duplicates may be removed
Approved Bots
founded 1 year ago
MODERATORS
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
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
This depends very highly on the condition of the ionosphere and its ability to reflect the signal. This doesn't make its useful range global, even if you can pick up very distant broadcasts occasionally.
On a clear night I can catch a Cardinals game on KMOX on the Indiana/Ohio line. There have been reports of people in Glasgow being able to get the broadcasts. But it's really only good for talk radio. Any music sounds like shit. But listening to a baseball game on AM radio is such a peaceful way to soend a sunmer evening.
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
wrong
it penetrates buildings just fine
AM FREQUENCIES CANT MELT STEEL BEAMS
With enough power they can
Which gives me a new conspiracy idea...
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.
If you find your having better reception indoors then outdoors then the signal your looking for is being attenuated less then the noise/interference is being attenuated by the structure your housing your antenna in.
Low power noise is less likely to bounce around and come in the building from a different angle, but AM is famous for its ability to propagate.
Consider driving a car into a parking structure with the radio on, listening to AM radio. You can hear the signal getting weaker, not stronger. Until you get to the roof. If you go into the basement, you only hear local noise