http://www.ece.ucsb.edu/courses/syllabi/PROTO.pdf
view the signal and frequency output of transmitter with oscilloscope
http://www.qsl.net/k6ls/rfsampler.html
Frequency range of 150KHz to 12MHz over 5 ranges. may be amplitude modulated by internal 800Hz tone with approx. 30% modulation. Mains powered unit has maximum 4V pk-pk adjustable output level.
http://www.vintage-radio.com/projects/signal-generator.html
makes buzzing sound when strong enough RF field is detected
http://www.ee.washington.edu/circuit_archive/circuits/rfsniff.txt
http://www.uoguelph.ca/~antoon/circ/rftls.htm
measuring admittance of an ac circuit that varies with level
http://www.omega.com/literature/transactions/volume4/T9904-13-RF-CAP.html
The crystal radio works best with a long, high outdoor antenna. This page describes different such radios and amplifiers.
http://www.techlib.com/electronics/crystal.html
http://www.intio.or.jp/jf10zl/12bh7.htm
using ordinary AM radio receiver.
http://www.anatekcorp.com/ttg/tiptrick.htm#Testing remote control using ordinary AM radio receiver