One way to hold this word: picture someone walking across a field with a hand full of seed, swinging their arm so the seed lands spread out over a wide strip of ground. Nothing is aimed at one spot; everything is sent out broadly. That is the picture inside broad + cast, and it is still the picture when a voice or a programme goes out — one person speaks, and the sound lands across a whole country at once. A broadcaster, in every use, is whatever does that : a machine, a person, or a company.
From the word’s history
Wiktionary derives broadcaster from broadcast plus the agent-noun ending -er, and its own first two senses of the word are agricultural: the machine that spreads seed, and (obsolete) the person who sows by scattering rather than by drilling.
Wiktionary 記錄 broadcaster 是 broadcast 加上表示「做這件事的人或東西」的 -er，而且它自己列出的前兩個意思都是農業的：撒種的機器，以及（已廢）用撒的方式播種的人。所以「撒種」不是我們硬套的比喻，而是這個字原本就有的用法。
Wiktionary entry for broadcaster (kaikki:3f6f69a190036ae4:983738194:29123): "From broadcast + -er (suffix forming agent nouns)"; senses 0-1 labelled (agriculture).
登入就可以看每一支怎麼連回核心畫面。