Russians still use extremely low frequencies for communication with submarines (an unidirectional communication system called "Zevs"). Transmitter is located on the Kola Peninsula, frequency is 82 Hz, bit rate is a few bits per minute, power consumption is in the multi-megawatt range. Waveguide is formed by the surface of the earth and the ionosphere.
I'd like some intuition --- is that very low frequency? Is that very high power? Can I have some context for how I should think about 82 hz and multi megawatt? (For example, I know that few bits a minute = well, that's a couple ASCII characters a minute)
If you don't already know just how low 82 Hz is - then the lowest frequency band you're probably familiar with is AM radio. Which uses around 1,000,000 Hz.
And as others have mentioned, yes, megawatts is a lot. That's the same order of magnitude as what most power plants produce.
And your power points in your house use 50 to 60Hz, depending on where you're from - and almost nobody even considers that "radio", even though technically it is.
Typically antennas for radios are 1/4 wavelength of the transmission frequency long (for various reasons but mostly related to transmission efficiency).
So as comparison, the 2.4GHz WiFi/Bluetooth radios in your phone have a 125mm wavelength so probably have 32mm long antennas (most likely folded in interesting ways to make then physically shorter). Old school 27MHz CB radios have an 11m wavelength, so ~2.7m antennas (in practice, at least on car mounted antennas, they'd coil some of that length up at the base out in the middle of they antenna, to keep the size down to 5 or 6 feet.) An 87Hz radio has a 3,500km long wavelength, so would want (for peak efficiency) an antenna almost 1000km long.
On top of that, power requirements to get a certain range go up with the square of the distance. Your phone WiFi probably maxes out at 200mW at it's 125mm wavelength and gets maybe 200m or less of max range. It's about 20,000km to get halfway around the planet, so ignoring a bunch of other important things, that's 100,000 times as far you'd need to transmit with 10 billion times as much power to get the same signal strength at that distance. That'd need ~2GW. Your phone battery wouldn't;t last long trying to do that...
(There's another complication abiyut the power requirement changing with wavelength, but I'm not quite enough of a radio geek to know that and the numbers I quickly googled up doin;'t make much sense, so...)
Here are some names we give to radio bands. These names are somewhat dated, as even “high” frequency is pretty low.
Low Frequency (LF) (30 kHz to 300 kHz)
Medium Frequency (MF) (300 kHz to 3 MHz)
High Frequency (HF) (3 MHz to 30 MHz)
Very High Frequency (VHF) (30 to 300 MHz)
Ultra High Frequency (UHF) (300 MHz to 3 GHz)
HF is used by amateur radio operators to communicate around the world, and has sufficient bandwidth to carry voice or low speed data (300 bits per second). Commercial airliners use HF over the oceans too. Probably some military stuff too.
Most other radios on the planet is operating on a higher frequency, in VHF/UHF or higher.
As for power, 100 watts is enough to send an HF signal around the globe. Commercial AM radio stations might operate up to 50,000 watts, so a megawatt is a lot more.
82Hz is an E2, the 19th white key from the lowest on a piano. [1]
So it's fairly low but completely audible.
For megawatts, imagine a million bookshelf speakers playing the lowest note they can play, or 10,000 subwoofers playing the highest note they can play. Most people listen to music at less than a Watt power.
I certainly wouldn't want to live next to that transmitter.
You're fine with hojillions of neutrinos zipping through you. It's not just about power, it's about interaction. How's living near that 82Hz transmitter compare to constantly living around electrical wires acting as 60Hz transmitters? Or a substation, for that matter?
You know that hum you get when mains powered audio get gets a certain kind of interference? That's 60Hz (or 50Hz depending on where you are) of moving air. It's not the 50Hz electromagnetism you h4ear though, it's that getting picked up by the amplifier and played out through the speakers which move the air.
87Hz is right about the second lowest F key on a piano. (the 21 key up from the lowest note on an 88key piano), or the low E string on a guitar at the first F fret.
Nah, it’s electromagnetic & your ears are too small to intercept the transmission to any kind of significant extent.
A few MW sounds a lot, but the inverse square law applies - once you get to the ocean the power density is going to be very low. Plus penetration into the ocean itself isn’t going to be great - there’s an impedence mismatch between the water and the air.
