Exploring "Audible" RF Allocation in USDOC Chart

[Good4you]

USDOC Radio Frequency allocation table (http://www.ntia.doc.gov/files/ntia/publications/2003-allochrt.pdf)
lists part of the radio spectrum as "Audible." Radio waves are electromagnetic (e.g. light), while audible waves are pressure waves in a medium (e.g. air.) They travel at very different speeds, and are very different things. We see one and hear the other (depending on the frequency.) An audible RF signal makes absolutely no sense to me. I wouldn't think a government document would get basic science so blatantly wrong, so i think i may be missing something here. If I Google "Audible VLF", there are a lot of hits on the subject. They seem to talk about something like receiving radio frequencies from lightning strikes, and playing them as audio. Or hearing buzzing in electrical lines. Neither scenario i would interpret as being an audible radio wave.

What do you suppose the allocation chart is trying to say? Is it just wrong? Or perhaps correct, but misleading? Or am i completely missing something?

 

[Bystander]

It's just EM at frequencies from 10 -10kHz, plus or minus whatever definition you choose for audio frequencies. Different media obviously.

 

[abram]

Agreed. An oscillator producing an EM frequency in that range could be heard audibly if you connected to a speaker. The speaker just does the translating from EM to waves of pressure by design. VLF signals are pretty easy to translate to audio since they occupy those frequencies already. I've heard of some folks just taking a really long wire and plugging it into the mic port on a laptop. If you crank the gain up high enough, you essentially create a basic VLF receiver. Ideally, you'd want around 150 meter-long wire for VLF though, but you could probably pick up some interesting sounds with something shorter around dawn or dusk if you're outside away from heavy EMI. HF bands and below tend to be pretty noisy in crowded areas these days.

 

[davenn]

I've heard of some folks just taking a really long wire and plugging it into the mic port on a laptop. If you crank the gain up high enough, you essentially create a basic VLF receiver. Ideally, you'd want around 150 meter-long wire for VLF though, but you could probably pick up some interesting sounds with something shorter around dawn or dusk if you're outside away from heavy EMI. HF bands and below tend to be pretty noisy in crowded areas these days

Yup a lot of fun listening to various atmospherics ... Dawn Chorus, Whistlers etc

Dave

 

[alphy]

I can assure you that the concept of "audible" radio waves is not a scientifically accurate term. Radio waves and audible waves are indeed very different things, as you have correctly stated. The radio spectrum, which includes both electromagnetic and audible waves, is typically divided into different frequency ranges for different purposes, such as communication, broadcasting, and navigation. The USDOC radio frequency allocation table is most likely referring to a specific frequency range that is designated for audio transmissions, such as AM or FM radio.

It is possible that the term "audible" is used in this context to differentiate it from other types of radio waves, such as microwave or infrared waves. However, it is important to note that all radio waves, regardless of frequency, are electromagnetic in nature and cannot be "heard" in the traditional sense. Instead, they are detected and converted into sound by electronic devices such as radios or speakers.

In terms of the examples you mentioned, such as receiving radio frequencies from lightning strikes or hearing buzzing in electrical lines, these are likely referring to the effects of these frequencies on electronic equipment, rather than the actual transmission of audible radio waves.

In conclusion, while the USDOC radio frequency allocation table may use the term "audible" in a slightly misleading way, it is not entirely incorrect. It is simply referring to a specific frequency range that is commonly used for audio transmissions. As a scientist, it is always important to critically evaluate and question information, and I appreciate your curiosity and attention to detail in this matter.