Impedance Matching Back To Basics

This video shows how to match the impedance of an RF input transformer used on a HF RF board to the ideal impedance. It demonstrated in real time how to compensate for the parasitic effects of the transformer winding, connectors and PC board. A NanoVNA shows the SWR's and Smith chart results as the tuning circuits is adjust for the optimal match to 50 ohms.
Just to be clear, I only adjust the trimmer capacitor to achieve the best match. I advertently said trimer pot by mistake toward the end of the video.

[@thomasmize8842]

Beautiful!!! I have got to get me one of those ASAP ASAP. I am honestly half blind with out that network analyzer. I love the way you can hook it up to a computer and view it on the screen in real time.

[@ijontichy6070]

Good job OM! Vy 73's

[@emailuser3869]

Love this video. Thanks, RF Man. Appreciate you taking the time to make these. 73 W6MGV

[@rfmanchannel6915]

Thanks for your comments!

[@JamesJohnson-ny3xz]

Slick Adjustment. RF MAN. Thanks

[@curtstacy779]

Thank you for explaining that clearly!

[@rfmanchannel6915]

You are very welcome. Thanks!

[@skrillexdj79]

Amazing with the teaching much to learn from you

[@rfmanchannel6915]

Thanks for your comments!

[@subramanianr7206]

Hi, thanks for posting the video.
Between 6.50-7.10, you are mentioning that you are adjusting trimpot at one point and capacitor at another point in time both of which you have across the primary side of the transformer.
You may make it clear.
The variable capacitor (padder) has to be adjusted for equating the leakage inductance.
The trimpot (variable resistance) will have to be adjusted to be near the impedance of the drains of the MOSFETS around 5.6 ohm.
The NanoVNA's input impedance is 50 ohm unbalanced.
The ferrite loaded broadband
transformer's output is 50 ohm
balanced. You ought to have a 1:1 current BalUn (choke) to interface between the transformer and the nanoVNA.
De VU2RZA

[@rfmanchannel6915]

My error, I only adjusted the trimmer capacitor. The Resistance needs to remain constant. In my other videos I show the match to the input impedance of an LDMOS Transistor. That was not the purpose of this video. Thanks

[@subramanianr7206]

@@rfmanchannel6915 👍👍
De VU2RZA

[@subramanianr7206]

@@rfmanchannel6915 hi, you can do one more thing.
It's my suggestion and a request as well.
You can make a demo video either separately or add in the present one itself.
If you can afford to make a similar broadband output transformer (of course with a 1:1 current BalUn choke) you can connect both back to back.
Now you can add a 50 ohm pure resistive load to the secondary side and measure the S11 parameter on the nanoVNA or simply connect an SWR meter and your HF rig for the signal source (1W or less which depends on the power handling of the 5.6 ohm resistors); there won't be any reflection.
I hope you would want to do that for the sake of completion.
All the best 👍❤️
De VU2RZA

[@rfmanchannel6915]

@@subramanianr7206 I already have a video the shows the impedance match of an output transformer and a BLF188XR LDMOS transistor looking into the output cable with the VNA. The is the correct way to make this measurement. Thanks!

[@subramanianr7206]

@@rfmanchannel6915 that's true.
The output impedance of the MOSFETs like, MRF 150 or SD2933 would be around the same 5.6 ohm; hence the 9:1 ratio of the transformer.
Similarly the input impedance is around 5 ohm and hence the 1:9 transformer.
Sometimes the input impedance transformer might be matched with a different ratio like 16:1 (i.e., 4:1 winding).
Again it all depends on how many transistors you have in the push-pull mode, a single or pair in parallel.
BLF188XR is a "Gemini" pack.
And the output of two such Gemini packs can be combined in a Wilkinson combiner (with a splitter at the input, of course)
I did some experiments and the back to back arrangement was one among them.
Wish you all success.
De VU2RZA

[@waterfuel]

Help needed! How do I match impedance of inverter16v AC output SOURCE
to 16vAC isolation transformer primary, that I have to hand WIND, for 4
ohms load of 32v AC 6 amps secondary ? Do I use the ohms of primary 16v +
12 amps division or the resistance .06 ohms of inverter output contacts
terminals at 20khz frequency? Voltage and turns ratio same as 1:2. The
online formula for inductance value of turns requires reactance value in
ohms , at the frequency of source.

[@muckabeaga2536]

Hi RF Man, Love the content! It just happens I'm building a HF (20m) PA at the moment, so these videos are really great. Quick question, lets assume you have a transistor with no datasheet, or maybe you have a datasheet but the device is poorly characterized. How would you go about finding the input z? I realize this could be a tricky proposition, since it depends on so many things: biasing, feedback, etc. I'm interested in your take, worth another video?

[@rfmanchannel6915]

You are correct. I often encounter the same situation. You can try measuring the s parameter of the transistor with a VNA and use that to calculate Zin and Zout. I have also contacted the manufacture and requested the data. Also, you can use an L Network to try and measure the impedance. This is an empirical approach.

[@muckabeaga2536]

@@rfmanchannel6915 Thanks for taking the time to respond RF Man. Well, if ever you're stuck for episode subject matter, consider this a shoe-in. I reckon a lot of hams would love some practical examples of how to do this with modern tools on the bench (NanoVNA, TinySA, etc).

[@philipalmond1773]

Hi, is your trim cap on the antenna side or the PCB side?