Jun 29, 2011 · 26 notes & . June 29, 2011 Germanium Diodes.More Details II. Question 3: Why use a germanium diode in a crystal radio set? Diodes by very function are able to take an AM waveform and recover the audio signal by removing the unwanted half of the AM signal. 1. If the forward drop is around 0.6V and the reverrse drop is infinite, it's probably a plain silicon diode. 2. If the forward drop is around 0.6V and the reverse drop is measurable, say less than 30V, it's likely a zener. 3. If the forward drop is 0.5V or less it's either a Schottky or, if it's really old, a germanium diode. A germanium-based diode might be lower, around 0.3V. The type of diode also has some importance in defining the forward voltage drop; light-emitting diodes can have a much larger V F , while Schottky diodes are designed specifically to have a much lower-than-usual forward voltage. This means that there is a small voltage across a conducting diode, it is called the forward voltage drop and is about 0.7V for all normal diodes which are made from silicon. The forward voltage drop of a diode is almost constant whatever the current passing through the diode so they have a very steep characteristic (current-voltage graph).