Hertz to Megahertz

It is largely a historical accident. Early generators in the US settled on 60 Hz because it divided neatly by common motor pole counts and worked well with the 110 V supply Edison promoted. Germany standardized on 50 Hz with a 220 V supply, and colonial-era wiring spread each standard across continents. Changing now would mean replacing every motor, transformer, and clock in the country — so both standards persist.

Concert pitch A4 = 440 Hz was standardized internationally in 1955, but some musicians insist 432 Hz sounds warmer or more natural. There is no physics-based reason 432 is special — it is 8 Hz lower, which shifts every note slightly flat. Historical tuning varied wildly (baroque pitch was often ~415 Hz). The debate is real in music circles, but the claimed health benefits of 432 Hz have no scientific support.

In 1887 Hertz built a spark-gap transmitter and a loop antenna receiver in his lab in Karlsruhe. When the transmitter sparked, the receiver — across the room with no wire connecting them — also sparked. He measured the wavelength and speed, confirming they matched Maxwell's theoretical predictions for light. Hertz was 30 years old. Ironically, he called the discovery of no practical use.

Older magnetic-ballast fluorescent tubes ignite and extinguish twice per mains cycle (100 or 120 times per second) because AC current crosses zero twice per cycle. Most people can't consciously see 100 Hz flicker, but it can cause headaches and eye strain. Modern electronic ballasts drive the tube at 20–40 kHz, eliminating visible flicker entirely.

About 20 Hz under ideal conditions, though sensitivity at that frequency is poor — you need extremely high sound pressure to perceive it. Below 20 Hz is infrasound: you cannot hear it as a tone, but at sufficient intensity you feel it as chest pressure or unease. Pipe organs exploit this: their longest 64-foot pipes produce notes around 8 Hz that you feel more than hear.

IBM needed a clock that could derive both the CPU timing and the NTSC color-burst frequency (3.579545 MHz) for the built-in composite video output. Multiplying the color-burst frequency by 4/3 gave 4.77 MHz — a convenient compromise that let one crystal oscillator serve two purposes. The weird number was pure engineering pragmatism, not performance targeting.

The 433.05–434.79 MHz range is an ISM (Industrial, Scientific, Medical) band that is license-free in most of Europe. Cheap remote-control key fobs, weather stations, garage door openers, and IoT sensors all crowd into it because you can legally transmit at low power without a radio license. In the US, the equivalent unlicensed band is 315 MHz, which is why European and American car key fobs are not interchangeable.

AM encodes audio by varying the wave's amplitude, which is vulnerable to electrical interference (lightning, motors). FM varies the frequency instead, making it inherently noise-resistant. FM also has a wider channel bandwidth (200 kHz vs. AM's 10 kHz), allowing it to carry the full 20–15,000 Hz audio spectrum in stereo. The MHz carrier frequency itself isn't what improves quality — it's the modulation method and bandwidth.

Intel and AMD marketed processors by clock speed — 500 MHz, 1 GHz, 2 GHz — implying faster was always better. By 2004, Intel's Pentium 4 hit 3.8 GHz but ran so hot and consumed so much power that performance-per-watt cratered. The industry pivoted to multi-core designs: instead of one core at 4 GHz, you got two or four cores at 2 GHz each, doing more total work with less heat. Raw megahertz stopped being a useful buying metric.

Bluetooth operates in the 2.4 GHz ISM band (2,400–2,483.5 MHz), which is reserved globally for unlicensed use. This avoids the need for regulatory approval in each country. The trade-off is sharing the band with Wi-Fi, microwaves, and baby monitors. Bluetooth mitigates interference by hopping between 79 channels 1,600 times per second — if one frequency is jammed, it has already moved on.