so ive been wanting to do a proper homebrew build for ages and finally sat down last weekend and put together a crystal set basically following the ARRL handbook design but with some mods i found on a old QRP forum thread from like 2009. wound my own coil on a pvc pipe former, about 60 turns of 26awg enamel wire, and used a 1N34A germanium diode i had rattling around in a parts drawer.

it picks up a few AM broadcast stations which is cool but the selectivity is pretty terrible — two of the stronger stations are bleeding into each other pretty bad. i added a small variable cap i pulled from an old transistor radio to tune it and that helped a bit but not much. using a long wire out the window, maybe 15 meters or so, and a ground to the water pipe.

not sure if the coil needs more turns or if the problem is just the antenna being unbalanced or what. anyone actually built one of these that can point me in a direction? i know its a simple circuit but clearly im missing something

the selectivity issue on crystal sets almost always comes down to the Q of your tank circuit and how the antenna is coupled into it. if you're tapping the antenna directly to the top of the coil you're loading it down heavily and that kills Q pretty fast. try a tapped coupling — maybe 5 or so turns from the bottom end of the coil as a separate antenna loop and see if that cleans things up. also 15 meters of wire hanging out a window with a water pipe ground is going to be a pretty lossy setup, not great but not terrible for broadcast either.

the 1N34A is the right diode for this so thats not your problem. i built one years ago using a quaker oats tube as the former and got reasonable selectivity just by being careful about the antenna coupling ratio. takes some fiddling honestly.

yeah selectivity on crystal radios is kind of just... rough in general unless you go dual tuned or something more complicated. ive messed around with a few of these and the coil winding is pretty critical, even how tightly you wind it matters. also what are you using for headphones? high impedance phones make a noticeable difference, the low impedance stuff you get from modern earbuds wont work nearly as well with a simple diode detector like that