参考
https://www.electronics-tutorials.com/basics/wide-band-rf-transformers.htmDesigning wide band rf transformers
In the design of these kinds of wide band rf transformers the primary reactance is usually around 5 times the primary impedance. With a 200 ohms to 50 ohm transformer, we would allow a reactance of 1,000 ohms at the lowest frequency of interest. Just as an example consider we were building a broad band amplifier for the amateur bands and going down as low as 1.8 Mhz.
For this example we would need bi-filar windings which have a reactance of 1,000 ohms at 1.8 Mhz, this means a required inductance of around 88 uH. A look through the Amidon data book tells me that ferrite toroid FT-50-61 as one example can provide me with an AL factor of 68mH / 1000 turns.
This means if 1,000 turns were wound on the toroid it would give us 68 mH. Yes that IS milli-henries, these are ferrite toroids.
Calculating turns for wide band rf transformers
To wind a wide band rf transformer with an inductance of 88 uH (yes that's micro-henries) which is in fact 0.088 mh we use the following formula:
Turns = 1,000 X SQRT (L in mH / AL factor) = 1,000 X SQRT (0.088 / 68) = 36 turns.
Our wide band rf transformer needs 36 turns to achieve an inductance of 88 uH.