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Registered Member #570
Joined: Wed Mar 07 2007, 03:41PM
Location: Winchester Uk
Posts: 42
To work well at 4MHz it will have to only have a few windings spaced well apart on a reasonable size core, say 8-16 turns maximum. It will also have to have a low resistance burden and have thick wire. You need to keep its self resonant frequency much higher than your 4Mhz frequency, and this is why only a few turns are possible.
Registered Member #570
Joined: Wed Mar 07 2007, 03:41PM
Location: Winchester Uk
Posts: 42
@tritium
Its not an iron powder core but ferrite. That table is for iron powder.
Fairite type 43 may work well.
Epcos N30 would also work, I've used this with good success with 8 turns for measurments up to 30MHz.
I also made a current sense transformer with 25 turns with good results. Both of these transformers used an Epcos N30 B64290L40X830. I cannot remember at what frequency it was flat to, but I think it was well over 10MHz before I started to see a resonant rise.
They had a low resistance burden with a series resistor in the output to give a 50R output impedance to drive a coax. At the other end was a 50R resistor to terminate the coax. This gives a flat response without ringing.
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current transformer at 4mhz
