Impedance matching with L and C

Thread Starter

Nailer

Joined May 11, 2021
7
Hi guys, I need maximum power transfer between 7 and 8MHz. I am quite new to impedance matching and I need help calculating components (L and C) and in which configuration I should put them into the circuit to get to 50 ohms. There is a pretty nice link for that but some skipped steps make me confused.

So basically I need help with how should I choose the configuration of L and C and how to calculate those values. I would probably order variable capacitors and inductors to fine-tune it also with VNA. All of the data is in the picture of measurement.

Thanks.

Capture.JPG
 

Thread Starter

Nailer

Joined May 11, 2021
7
Thank for the literature it will come in handy for understanding, I also found that the easiest way is using SimSmith and the tutorial can be found here. link
 

BobaMosfet

Joined Jul 1, 2009
1,768
Hi guys, I need maximum power transfer between 7 and 8MHz. I am quite new to impedance matching and I need help calculating components (L and C) and in which configuration I should put them into the circuit to get to 50 ohms. There is a pretty nice link for that but some skipped steps make me confused.

So basically I need help with how should I choose the configuration of L and C and how to calculate those values. I would probably order variable capacitors and inductors to fine-tune it also with VNA. All of the data is in the picture of measurement.

Thanks.

View attachment 237988
This may help-

Inductance Calculations
Author: Frederick W. Grover
ISBN-10: 048647440-2

Reference Data for Engineers: Radio, Electronics, Computers and Communications; 9th Ed,
Author: Mac E. Van Valkenburg
ISBN-13: 978-0750672917
ISBN-10: 0750672919
 

Irving

Joined Jan 30, 2016
1,496
what bit of kit did the Smith chart? The numbers given for the markers I believe gives you all you need to work out the parallel inductance or capacitance, centred on 7.5MHz. A quick calculation with the impedance version of the Smith chart shows it can be matched with a 12.93m x 50ohm transmission line (@7.5MHz) and a 97p series capacitor, but 13m isn't very practical so you need to work with the admittance version of the Smith chart to find the parallel LRC needed.
 
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Irving

Joined Jan 30, 2016
1,496
Some other useful resources:
Maxim tutorial 742
RF Circuit Design - [Ch2-1] Resonator and Impedance Matching

This is a brilliant web site....an online Smith chart - I've not seen this one before but its high on my best-ever online tools now!

Here's two plots using a transmission line and series capacitor at 7 and 8MHz
1620828041374.png1620828095539.png

Playing around I got this pair of plots... which is the closest I could get after 10min of playing to get (looking into the system from the RH side) R close to 50ohm and the reactance roughly equal each side of 0.- YMMV! But because your end device has such low series R the losses are high... Or is this the source? Its not clear. If so this is all rubbish, but the technique is still valid...

Edit: found a better solution thats even smaller reactance...
smith1.JPGsmith2.JPG
 
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Thread Starter

Nailer

Joined May 11, 2021
7
Thanks for the reply, I have read through the material you posted.
Oh, yea that site seems really practical. But I found a java program called SimSmith that does almost the same thing and is nicer to use, at least to me.
It seems that my answer lies in the L-Matching network which can easily be made with SimSmith or the online tool you provided.
And I had done matching the circuit with SimSmith like this (parallel C followed by series L, with shown values):
SimSmith L-Matching network for preliminary full setup with 100nF RF carpet and DC connected.JPG
 

Irving

Joined Jan 30, 2016
1,496
Thanks for the reply, I have read through the material you posted.
Oh, yea that site seems really practical. But I found a java program called SimSmith that does almost the same thing and is nicer to use, at least to me.
It seems that my answer lies in the L-Matching network which can easily be made with SimSmith or the online tool you provided.
That looks good! Remember t run the matching at both ends. I started by finding the best match for the centre point of your two data points, ie 2.25 - j26.2 @ 7.5MHz then tweaking it to balance +/- reactance at 7 and 8MHz and the relevant data point.
 
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