Hello everybody,

I have a question about RF transformers. Normally, a decoupling capacitor is used to decouple different amplification stages. Despite this, I have seen that the same works can also be done between transformers like these below:

https://www.coilcraft.com/en-us/products/transformers/wideband-rf-transformers/th/wb_th/

What is the functional difference between decoupling with capacitors and transformers of this type? Can I use these transformers in place of the capacitor to couple a voltage amplifier stage and a current buffer without obtaining voltage losses?

Thank you

 

You will have some losses which ever way you choose but the big advantage of transformer coupling is that you can use the transformer primary to secondary turns ratio to match the output impedance of one stage to the input impedance of the next stage, making the whole circuit much more efficient.

 

Transformers also provide isolation and in special cases (IF transformers) act as coupling means and tuning means when used in conjunction with a coupling capacitor.

 

An RF circuit uses a transformer because it's ability to resonate for a specific goal and turns ratio can adjust AC sine voltage both up or down for a particular current while promoting certain harmonics and reducing other harmonics. The role of filter, transformer, impedance matching and wave shaping can be an interesting accomplishment. The use of a wideband transformer is ok but not highly resonant, limited less robust. The compare and contrast on the use of parts is specific to the goals and application so getting there is often more convenient to slug tune or add or remove windings, some satisfaction with diy hand made coil. The introduction and exploration is sort of an inventory and concept, the contrast is within the variations of transformer configurations and which type might work for you and why. The example of a qrp crystal tuning and stage impedance matching can be done with a kit inexpensively, by narrowing the study to an appropriate transformer we add more complexity however it gives more options to overcome issues that RF waves have with interstage distortion and loss.

http://www.arrl.org/files/file/Technology/tis/info/pdf/8405015.pdf

 

Thanks for the answers. So if i use a ratio 1:1 the impedance between primary and secondary are same, but if i use 1:4 i have four times impedance in output right?

 

hi Dani,
Checkout this link.

E
https://www.google.com/search?client=firefox-b-d&q=transformer+impedance+ratio+formula

 

Thanks for the answers. So if i use a ratio 1:1 the impedance between primary and secondary are same, but if i use 1:4 i have four times impedance in output right?

No. The Impedence is proportional to the Square of Turns. Turns Ratio 1:4 will match Impedence 1:16.