dave wrote:
On 01/25/2014 01:21 PM, Jerry Peters wrote:
dave wrote:
On 01/23/2014 06:05 PM, Michael A. Terrell wrote:

dave wrote:

On 01/23/2014 06:45 AM, Michael A. Terrell wrote:


It is not a switch or a valve.


It's a solid state diode that oscillates. DC in, and ~10 GHZ out.
Search on Gunnplexer. You see them on automatic doors in almost every
store. A microwave mixer diode takes a sample from the Gunn diode and
compares it to any reflected signals. This results in a low frequency
signal that is detected, amplified and signals the door to open. How can
a passive diode do that?


Like I said. You can hit a piece of quartz with a hammer and it will
oscillate; that doesn't mean it's considered and active device. An
active device uses one signal [current, voltage] to control another. As
in amplify or switch. Thermionic valve, transistor, SCR, Triac is what
we are going for.


An active device uses one signal [current, voltage] to control another.

So a relay is an active device?


A relay is a solenoid (no) and a switch (no).

But it controls one signal with another.

What about a PIN diode, or even an ordinary switching diode. They've
been commonly used to switch an small ac signal with a dc voltage for
*years*.