Experiments with Transmission Line Baluns

[@Stefanev]

Another great video. Thanks!

[@layt01]

Thank you, I learned a lot.

[@ghlscitel6714]

Great presentation! Did you ever simulate a broadband coax balun wound around a toroidal core to function as a sheath wave choke with LTspice?

[@FesZElectronics]

I don't think I have, but I will probably expand this series in the future

[@ghlscitel6714]

@@FesZElectronics Thank you for your reply. Would you have any advice on how to start writing the spice commands? I may get a chance to start myself. By the way, I remember having seen a capacitance meter and an inductance meter in one of your videos. Can you recommend them? Which types are they?

[@FesZElectronics]

What I found out in the mean time is that if you want to model the inductance you get from a ferrite core - you can add it as an inductor in parallel with the transmission line - like the magnetizing inductance is modeled with a normal transformer. Maybe this will help. As capacitance meter I use a CM9601A (not sure of who the manufacturer is though) and for inductance I usually use an AX588B (from Axiomet) - these are not the best tools but they are relatively low cost.

[@FesZElectronics]

Regarding the modeling, see fig.3 and the associated comments of course, maybe this will help - www.highfrequencyelectronics.com/Dec07/HFE1207_GrebennikovPart1.pdf

[@ghlscitel6714]

@@FesZElectronics Great inspiring article, thanks for sharing. By the way, I very much like your work. Greetings from Germany to Romania.

[@StreakyP]

my concern is what happens in the amateur radio world where we have a 4:1 half wave transmission line balun feeding the balanced 300ohm folded dipole... BUT UP AT THE ANTENNA THERE IS NO EARTH/GROUND AVAILABLE AT THE BALUN TO GROUND THE CO-AX SCREEN TO SO IT GETS LEFT FLOATING. How does this mess things up?.

[@R2AUK]

👍

[@demindor]

Also, a question. How did you specify the L parameter instead of Td parameter? LTSpice help file says that the length is derived from Td. And for lossy transmission line it's called Len, not L (L is for the inductance per unit length).

[@FesZElectronics]

Well, I used both L and Len in my definition; I know from the datasheet the Capacitance/1m; and knowing the characteristic impedance, you can determine the inductance/1m - Z=sqrt(L/C); so L=Z*Z*C; the delay per unit of line is sqrt(L*C); and the model finally multiplies this by the LEN value.

[@demindor]

@@FesZElectronics Yes, that works perfectly for lossy transmission lines. I was asking about the earlier section of the video, where you were showing lossless transmission line and moved from specifying Td (in nanoseconds) to specifying L (in meters). That's the part I don't understand. For example, 8:36 - you use Td parameter to indicate delay. 11:50 - you use L parameter to indicate length. Or was it just for illustrative purposes?

[@FesZElectronics]

Ah, sorry; yes, that was just to make the length clear... it wasn't a model that can be simulated.

[@demindor]

@@FesZElectronics Thank you very much for the clarification. Now it makes the perfect sense.

[@xDR1TeK]

My friend, i think it's time you jumped to ADS for this experiment.

[@FesZElectronics]

Not sure what ADS stands for...

[@cesarcantoral6100]

Great “infotainment “…..lol