Impedance matching circuit design with LTspice and Smith 4.1

This is a short video showing how to use LTspice to find the port impedance of a circuit and how to use Smith v4.1 to design a matching circuit. I also show how to export the s-parameters into a file for further processing

[@WolfmanDude]

Wow that is so great, until now used to draw and calculate the matching networks by hand! It worked perfectly, I really felt like an engineer from the future doing that!

[@michaelreuter7577]

Where can i download the Smith 4.1 tool?

[@michaelreuter7577]

I have the rereflection coefficient and would like to import it into the Smith 4.1 tool. Is this possible and if so I would appreciate a short video.

[@nurhaida1983]

Hi. I'm just curious: how do you determine the 1nF capacitor at the input? Is it by using the C=Q/V equation or the Xc equation or both? I'm sorry if this is a weird question to ask😅

[@polprog702]

I think it was from the top of my head. At this frequency 1nF is a very low impedance. edit: from the Xc equation.

[@christianejikeomeje3145]

great tutorial, i tried same using my bjt transistor deign, but am getting negative as my real part

[@polprog702]

Hm, that is weird, but maybe LTspice took the current draw in the other direction. Just drop the minus from the real part

[@malikusama4758]

any refrence for using this method for impedance matching?

[@polprog702]

You can use it to sweep a circuit across some band but I think QUCS-S is better for that as it does Smith charts and S-parameter plots

[@JonathanS-q7n]

@@polprog702 I used to use QUCS, but it gives weird error reporting. I change one capacitor value, it then shows an error. If I change it back to the original value, it still shows an error!

[@minazulkhan8287]

Great video. Drink some water u seems thirsty!!

[@hedleyfurio]

Agree - mouth noises spoilt an otherwise super video . He could use audacity with a plug in to remove these , or perhaps not have the mic pickup inside the mouth .

[@johndavis1465]

The circuit should have a capacitor coupling the output

[@polprog702]

that's true, though in practice I put a large one like 100n that has neglible impedance and dont always draw it

[@JonathanS-q7n]

@@polprog702 It will have a neglible impedance, but will change the DC operating parameters of the transistor, which will affect the matching?

[@JonathanS-q7n]

I would think it needs a capacitor at the output, between the 50 ohm resistor and collector. With 50 ohms and a DC voltage present, it will alter the DC load line!

[@polprog702]

@@JonathanS-q7n You're right, I did not notice that

[@smartsensing6563]

LTSPICE is not for RF use. you need to use HAM radio amateurs ' tool, way much better. probably 100 magnitude better.

[@polprog702]

It is for RF use if you understand its limits

[@nDarien]

Great video and great method to match the impedance!

[@oleglosev3510]

Nice info.. thanks!

[@dr-mnizam]

This video shows how to install LTSpice: th-cam.com/video/g5t4C2UdKJI/w-d-xo.html

[@alexgreysukh4875]

But how to install Smith 4.1 - it seems not free software.

[@rawanfarouk3498]

Hi if my center frequency is 900Meg what would my start and stop frequency be?

[@polprog702]

I think it can be anything, you can try 450 to 1800MHz