They did amazingly ingenious things to replicate the tuning coil, which was covered by a Marconi patent. The amateurs put other items to use: "[W]hen Quaker Oats began packaging its oatmeal in cylindrical cardboard containers, these tubes became the standard core for the tuning coil."
And they bought components from stores like this one:
At the time, anyone with this kind of inexpensive homemade equipment could transmit and receive signals at whatever frequency they wanted.
The amateurs got swept up in fierce currents of centralization and control, coming from many different directions - big corporations and new institutions of government were arriving on the scene at the same time. Secretary of Commerce Herbert Hoover took strong action to allocate the airwaves, backed up by Congress, in ways that would essentially protect all the major broadcasters and eliminate new entrants and marginal amateurs. Listeners were assured that they wouldn't have to buy new receivers that could tune in new stations.
I'm just starting to look into this early, pre-1920s history of radio. It seems to me that in this summer's 700 MHz auction many of these same historical themes are playing out in much the same way they did in Hoover's era. So far, I've identified three:
1. protection of incumbents (rich get richer, sweeping away amateurs and new entrants)
2. resistance to new technology (now, resistance to software-defined radios and dynamic auctions for use of spectrum)
3. military preemption (important in Hoover's time as now).
I'm sure there are more.
Douglas's description of the hero-amateurs, who were "radio" before it meant "broadcasting," is enthralling. It wasn't inevitable that we turned towards broadcasting in the 1920s, and it isn't inevitable that we reject new entrants providing internet-access-enhancing models today.