This is an excellent article, thank you for submitting it! I love how effortlessly this article delivered an intuition for why an ideal antenna length would be half of the wavelength of the signal you want to receive. I was also delighted by the point about how all methods of modulating a wave can be recontextualized as frequency modulation!
> I was also delighted by the point about how all methods of modulating a wave can be recontextualized as frequency modulation!
That's the classic way to think about it. Another way is to view the input as simply a sequence of voltage readings. Extracting a useful signal from that is an exercise in exploiting redundancy in noisy data. [1] Software defined receivers work that way.
Analog radio (AM, FM, etc.) is a hulking big carrier weakly modulated by the signal. Analog TV, which was AM video with FM audio, had 80% of the power in the carrier. Analog UHF TV stations often had multi-megawatt transmitters to overpower noise by sheer RF output. Digital broadcast TV transmitters output maybe 150KW, because the modulation is more efficient.
Modern modulation techniques are insanely efficient. It's amazing that mobile phones work.
I may not be understanding what part of the operation you are talking about. but radiated power? no transmitter had megawatts of radiated power. 50Kw for a fm broadcast antenna is a common number passed around. The huge "voice of america" shortwave station was 300Kw.
I have heard of military radars having megawatts of radiated power. but even then it was in the low megawatts.
For UHF television stations, the effective radiated power (ERP) is typically 1 Megawatt. That is accomplished (for example) with a 57 kilowatt transmitter and an antenna with 12.44 dB gain.
Up in the UHF TV bands, huge transmitter power was required. The FCC allowed 5 megawatts.[1] Few stations actually used that much power, but 1 MW was not uncommon.
Amusingly, over-the-air digital TV is making a comeback. The cable industry pushed prices up too high. But the "comeback" is to only 14% of the viewer base.
> Modern modulation techniques are insanely efficient. It's amazing that mobile phones work.
There's old modulation techniques that are crazy efficient too - the most obvious one being GPS. A small antenna, just 2cm short [1], is all you need to pick up and distinguish from each other the signal of up to a dozen different GPS and dozens of other (GLONASS, Galileo, BeiDou) navigation satellites. This is mind-blowingly nuts.
For modern high-bandwidth communication, microwave point-to-point links can achieve 65km range with barely 4 watts of RF energy - e.g. German Telekom's Skylink system connecting an aviation radio transmitter on the island of Helgoland with the continental backbone at Cuxhaven [2]. And actually that is way more power than required, half a watt is enough but they chose to go for higher power to achieve perfect reliability even in worst-case conditions [3] (does make sense, given how safety-critical flight radio communication is).
If all you need is satellite communication for a few bytes of information, a cellphone can send an emergency message to satellites anywhere on this planet (at least, where regulatory clearances allow for that) [4].
> If all you need is satellite communication for a few bytes of information, a cellphone can send an emergency message to satellites anywhere on this planet
This month, an unmodified Samsung S21 Ultra achieved 17mbit download speeds from a Starlink satellite, which is. Well, quite something. I do wonder what the upload speed would be.
I love the fact that GPS signals are below the noise floor; its only through correlating the complex modulation that you can find the signal. At least, that's how I understood it when I did my degree!
""…all methods of modulating a wave can be recontextualized as frequency modulation!"
That's the classic way to think about it. Another way is to view the input as simply a sequence of voltage readings."
Right. And modulation of any type produces sidebands as per Fourier! Do anything whatsoever to disturb a pure sine wave then math and physics dictates it so.
