Hello , i need to make with ferrite core a converter from 50 to 75 ohms , pretty like the tv one that come from Aerial 300 to 75 ohms , any help . Something like this in pictures , but lacks for details of turns etc...

There are several ways of winding transformers or baluns!

For a simple isolation transformer, you will need to calculate or measure the reactive inductance of each winding depending on the ferrite material you use!

So in theory? If your 50 ohm primary reactance equals to 4 turns, the secondary out will be 6 turns for 75 ohm!

Again, the ferrite material will play a major part in how it transfers power!

Please be aware that a ferrite like that will not pass more than a few Watts - the core becomes saturated and the SWR jumps off the scale once this happens. You may want to try winding the transformer on a binocular ferrite like the ones used in push pull amplifiers like BLF278, MRF9180 etc. if it is for high power - Enigma have a selection:
https://www.enigma-shop.com/inductors/f ... ansformers
You may also want to look at the twelfth-wave transformer if you're trying to match an antenna:
https://pa0fri.home.xs4all.nl/Ant/Eentw ... former.htm

thank you both freinds for the valuable reply . the adapter is used ONLY for reception , just an experiment .but i need to knowa formula to calculate that .i want to use in vhf i have few ferrite and a little vna and an lc meter, will that be sufficient .

Yes. You'll be fine. Are you sure that your receiver is 50Ω or 75Ω? What kind of antenna are you using? If it's a basic dipole, it'll be close to 72Ω at resonance. What feeder are you going to use?

In the case of reception, exact antenna match (usually) isn't going to be possible if you're tuning over a range of frequencies. You want to get an accurate match at the centre of the range of frequencies you want to tune, and as long as you're not tuning too far away, you'll get a reasonable match over the whole range.

Exact impedance matching really doesn't matter for reception. The difference between 50 and 75 ohms is tiny and would only give you 1.5:1 swr at worst. Not great for transmitting but no big deal for receive only. Like albert says your antenna will never be a perfect match to 50 or 75 ohms anyway so trying to match the impedance better than that is pointless. Plus the losses in the transformer will probably outweigh any gains you make from a better match.

yes for reception is best coax cable from car 100R less loses more sensitivity !

Sinus trouble and Yellowbeard , lnow exactly what i need . i am only experimenting and not more , i have a little vna and want to see things to learn a bit , just have an adapter of 300 ohms to 75 , and i want to convert that to 75 to 300 ohms , thats all folks...

if its for receiving you could try different capactors between the signal and ground, between the receiver and the aerial. I used experiment with older synthesised tuners, sometimes I can do that before the aerial socket, get abit better reception that way.

Yes everything is true. But I need to do it .never mind if I use it or no . I have to try with vna