"Steve Robertson" <steven_j_robertson(a)hotmail.com> wrote: Hi All should take a look at this site: http://uweb.superlink.net/bhtongue/ He goes quite a bit into the issues of the "diode knee". He talks quite a bit about matching of impedences. An unbiased diode has a quite high impedence. Slightly forward biasing the diode can make a better match since one can tap off the tank circuit at a better match. One can work backwards from the head set to the crystal and then to the tank coil. There is another type of diode that might even be better. They are called back-diodes. These are designed with a vary low zener voltage. The idea is that the zener can have a much sharper edge than the log based forward diode. Dwight