WEBVTT

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>> Okay. Now let's talk
about the antenna block.

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The antenna right here is what's

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used to receive the signal
in the first place.

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The antenna is a 2.4 or 2.6

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gigahertz antenna so they can receive
both of the possible frequencies.

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They come into this antenna which
is a quarter of a wavelength long,

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and underneath there's copper
underneath each of these strips.

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So, that this thing right here is
a microstrip as a transmission line.

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Now, the transmission lines are
normally modeled like this.

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Their model is a combination of
resistors, inductors, capacitors,

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and conductors G so that
each little distance

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along this transmission line can
be assumed to be a resistive,

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capacitive, inductive, conductive network.

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So that's a transmission line.

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Okay now, as the signal is
received by this antenna,

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the antenna has
a particular input impedance.

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On the other side, the amplifier has
a particular input impedance as well,

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and these two impedances
need to be matched at

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the stub and they wouldn't be and
so we have to manually match them.

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This thing right here is an open-circuited
stub that's used to impedance match

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the antenna to the transmission line and

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then the amplifiers also matched
to this transmission line.

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This particular transmission line
is a 50 Ohm transmission line.

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So, we need this antenna
to be matched to 50 Ohm's.

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The way we do it is we have

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a particular distance here and a
particular length of the stub.

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It's literally just a little stub
of copper that we

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cut with scissors and stuck down,

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this literally stuck it right down there

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so it's touching this transmission line.

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The length of the stub is
going to make it either

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capacitive or inductive depending
on the length of the stub.

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Remember that inductors and
capacitors create phase shifts.

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A phase shift is just a time delay.

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So as a little bit of signal goes
up this line and comes back,

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that's the time delay
that it experiences and

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consequently the phase
shift that it also obtains.

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So, once we get past this point,

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the antenna and this combination of

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impedance matching network are
now matched to a 50 Ohm line.