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00:00

just a short video for fun from the
shack here this evening to show how you
can visualize the operation of an
antenna tuner like this one here using a
vector network analyzer and setting it
up with a couple of displays each of
which will show you the operation in a
slightly different way so normally when
you use an antenna tuner like this
you're tuning up at a particular
frequency so we're going to do the same
thing with the VNA we'll set it up in

00:30

the zero span in this case at 7.2
megahertz now the analyzer is set up
with three displays but each display is
really just measuring s11 the reflection
coefficient but it's displaying it in
three different formats down here in the
lower right corner is the traditional
logarithmic magnitude of the s11 but
again we're in zero Spanish they're
gonna have a flatline the reflection
coefficient is also expressed as the
standing wave ratio where SWR which is a

01:02

the most common thing that hams will
look at so I displayed that here as well
and then thirdly we're also displaying
the reflection coefficient as the
complex impedance looking into the coax
so this is what the transmitter would
see on the Smith chart here at Smith
charts just to quickly a way of
displaying a complex number in this case
complex impedance
where we have essentially circles that
represent constant resistance and we've
got arcs that represent consequent

01:34

reactants both inductive and capacitive
reactance and the location of where you
are on the chart tells you essentially
the complex impedance so right now
before we start adjusting the tuner
we've got our marker sitting right out
our single point at 7.2 megahertz and
that's giving us a input impedance
looking into the coax of 20 ohms plus J
38 ohms so an inductive thirty-eight
ohms and a real part of plenty ohms and

02:04

that's what that point represents now if
I reach up and grab the capacitor
control on the tuner I can see a couple
of things
I can move the impedance that's seen on
the Smith chart kind of on an arc as we
adjust that capacitor I can also see the
return loss NSW our curves moving as
well if I grab the roller inductor of
the tuner and start adjusting that I can
actually see myself moving along on the

02:35

Smith chart as well as the other
displays now our goal is to get the
one-to-one SWR which will be achieved
when the input impedance is right here
in the center of the chart right at 50
ohms resistive so all we need to do is
essentially adjust our controls to kind
of get us there and you can see I adjust
my inductor down my capacitor back here
and get ourselves really close we're
really careful here and the zero in to

03:07

something very very close to just a 50
ohm resisted termination and if we look
here now I'm at forty nine point seven
ohms and about point four ohms of
inductive reactance and if we tweak that
a little bit more likely to get even
closer okay and with ourselves very
closely centered here we take a look at
our SWR plot and we're sitting at one
point zero zero eight two one and return

03:40

loss is 47 DB so we've achieved a really
really good match by simply tuning the
capacitor and inductor on the tuner and
visualize that a couple of different
ways well now that I've tuned up at my
desired frequency at 7.2 I've changed
the VNA to give me a span of 400 killers
so now we'll sweep from seven Meg to 7.4
megahertz which more than covers the 40
meter amateur radio band now of course
on the Smith chart I can see the input
impedance to my antenna system now what

04:12

I mean by that is the antenna the tuner
and the coax leading to the transmitter
and this is what that impedance looks
like over frequency and if I great I can
drag that marker around and actually see
what that impedes looks like at any
frequency within
sweep going back and forth okay of
interest to most hams would probably be
this plot right here which is showing me
my standing wave ratio or SWR versus
frequency I've actually put a pair of
markers here at the two-two-one SWR

04:43

points and this indicates that I've got
something in the neighborhood of about a
hundred and forty kilohertz of two to
one
SWR bandwidth so covering a lot quite
half of the forty meter amateur radio
band and of course of interest to most
RF engineers would probably be just the
log magnitude of the reflection
coefficient which is shoving down here
but all of these are essentially the
same measurement just displayed a couple
of different ways today's video was

05:14

basically just for fun but I do plan on
doing some more tutorials on the use of
VNA for various applications in the
future as well as it may be even some
tutorials on the Smith chart itself you
know an old tool that RF engineers have
used for many years but maybe maybe a
bit of a lost art these days in terms of
how you can actually use it manually so
people will cover that in some future
videos as well anyway if you like what
you see
now give me a thumbs up if you haven't
subscribed already please do so comments

05:45

are always welcome and thanks again for
watching see you next time

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