WEBVTT

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>> The last part of our circuit
is the diode detector.

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We have two diode detectors right here.

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One that's designed for 2.4 gigahertz

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and the other that's
designed for 2.6 gigahertz.

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The way the diode detector works.

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I'm just going to show you
the little circuit right here of these.

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The way the diode detector
works is the AC signal comes

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out of either one of the band-pass filters.

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Remember, we don't know
which one's going to

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have the signal. One or the other will.

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But AC signal comes in right here,

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goes through a diode and then
is integrated by a capacitor.

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The original signal that comes in is

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the black sine wave that
you see right here.

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That is VAC.

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Maybe, it's at 2.4 gigahertz in this case.

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The diode only allows
current to go one way.

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So it only allows the positive part
of our signal to get through.

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The red line right here
is the signal when it

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goes to the diode and that's
called halfway rectified.

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Rectified means that it's
turned right side up.

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In this case, only half of
the wave is passed through.

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Then, when it goes through this capacitor,

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the capacitor integrates
or averages that signal.

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So the dashed line is the DC voltage

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that's going to come out
of that capacitor VDC.

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Let's see where those are
in our diode circuit.

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So right here's my diode circuit

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VAC comes out of the band-pass
filter at this point,

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let's say it's 2.4 gigahertz.

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It comes into my system and
there's the diode right there.

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You can't see but it's
a little triangle thing like so.

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But there's the diode and that is

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half-wave rectified signal.
Here's the capacitor.

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It's just like the capacitors we had on

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the amplifier and it goes down to ground.

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The ground is underneath.

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Here goes down to ground and
then right there is going to be

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the DC signal that comes
out if it is 2.4 gigahertz.

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That signal then can go
into a comparator and be

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converted to a zero or a one
to be used by the computer.

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On this side, we have the same thing and
it's designed for 2.6 gigahertz where

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the AC signal comes in because the diode is

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integrated across the capacitor
and comes out as a DC value.

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Now, there are some other little parts
of this circuit too.

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These have short circuited
stubs and that impedance

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matches these 50 Ohm lines to
the diodes that are not 50 Ohm.

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There's 100 Ohm line here and
an open-circuited stub that match

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the impedance of this particular diode
to this particular transmission line.

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Another interesting thing
that you can see right here

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is because we had a little trouble
matching this particular one.

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We actually put two stubs on just to
help with the impedance matching.

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So, that's a picture of
our frequency shift keyed system.

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Let's look again to see where the
inductors and capacitors are.

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We've got our antenna right here.

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The transmission line is seen
as a series of resistors,

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inductors, capacitors, and conductors.

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We have capacitors right here
to block the DC signal from

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the AC and an inductor to keep
the AC out of our DC power supply.

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We have a surface mount
resistor right there in

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our 3dB coupler and then
we have a series of

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band-pass filters that
are made up of a set of

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effective resistors,
capacitors and inductors.

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Then when we get over to
the diode detector circuit,

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a capacitor is used again in order to
integrate my halfway rectified signal.

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So we've used a lot of capacitors
and inductors in the circuit.

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I just thought you might like to see it.