Application note from Mini-Circuits about transformers, this time the RF transformers. Link here (PDF)
RF transformers are widely used in electronic circuits for
* Impedance matching to achieve maximum power transfer and to suppress undesired signal reflection.
* Voltage, current step-up or step-down.
* DC isolation between circuits while affording efficient AC transmission.
* Interfacing between balanced and unbalanced circuits; example: balanced amplifiers.
from Dangerous Prototypes http://ift.tt/2wm9vSC