>> The last part of our circuit is the diode detector.
We have two diode detectors right here.
One that's designed for 2.4 gigahertz
and the other that's designed for 2.6 gigahertz.
The way the diode detector works.
I'm just going to show you the little circuit right here of these.
The way the diode detector works is the AC signal comes
out of either one of the band-pass filters.
Remember, we don't know which one's going to
have the signal. One or the other will.
But AC signal comes in right here,
goes through a diode and then is integrated by a capacitor.
The original signal that comes in is
the black sine wave that you see right here.
That is VAC.
Maybe, it's at 2.4 gigahertz in this case.
The diode only allows current to go one way.
So it only allows the positive part of our signal to get through.
The red line right here is the signal when it
goes to the diode and that's called halfway rectified.
Rectified means that it's turned right side up.
In this case, only half of the wave is passed through.
Then, when it goes through this capacitor,
the capacitor integrates or averages that signal.
So the dashed line is the DC voltage
that's going to come out of that capacitor VDC.
Let's see where those are in our diode circuit.
So right here's my diode circuit
VAC comes out of the band-pass filter at this point,
let's say it's 2.4 gigahertz.
It comes into my system and there's the diode right there.
You can't see but it's a little triangle thing like so.
But there's the diode and that is
half-wave rectified signal. Here's the capacitor.
It's just like the capacitors we had on
the amplifier and it goes down to ground.
The ground is underneath.
Here goes down to ground and then right there is going to be
the DC signal that comes out if it is 2.4 gigahertz.
That signal then can go into a comparator and be
converted to a zero or a one to be used by the computer.
On this side, we have the same thing and it's designed for 2.6 gigahertz where
the AC signal comes in because the diode is
integrated across the capacitor and comes out as a DC value.
Now, there are some other little parts of this circuit too.
These have short circuited stubs and that impedance
matches these 50 Ohm lines to the diodes that are not 50 Ohm.
There's 100 Ohm line here and an open-circuited stub that match
the impedance of this particular diode to this particular transmission line.
Another interesting thing that you can see right here
is because we had a little trouble matching this particular one.
We actually put two stubs on just to help with the impedance matching.
So, that's a picture of our frequency shift keyed system.
Let's look again to see where the inductors and capacitors are.
We've got our antenna right here.
The transmission line is seen as a series of resistors,
inductors, capacitors, and conductors.
We have capacitors right here to block the DC signal from
the AC and an inductor to keep the AC out of our DC power supply.
We have a surface mount resistor right there in
our 3dB coupler and then we have a series of
band-pass filters that are made up of a set of
effective resistors, capacitors and inductors.
Then when we get over to the diode detector circuit,
a capacitor is used again in order to integrate my halfway rectified signal.
So we've used a lot of capacitors and inductors in the circuit.
I just thought you might like to see it.