Making a suitable antenna for a crystal radio
The simplest antenna for a crystal radio is a long wire (say 10m), and up as high as you can get it. On the roof is best if you can get up there. The wire should be stretched out, not rolled up. Outside is best, to avoid signal loss in any metal in the building's structure. Make sure the antenna is attached with insulators at both ends. To make it simple, take your long wire, attach one end with an insulator. Unwind enough of the wire to reach the other end. Attach it there with an insulator as well, but don't cut the wire. Instead, use the remaining wire to connect it to your radio.


  I'm not getting any voltage registered


The voltages generated by a crystal are very small indeed, and they are at radio-frequency AC, so they may not show up on a simple voltmeter. You should be able to see the signal with an oscilloscope though.