开云体育

These are crazy expensive for what they are — even second hand and out of calibration.

As far as I can guess the CT-6 current probe is just a moulded miniature toroid with 10 turns of thin wire attached to an SMA terminated 50R coax.
Does anybody have an insight what ferrite material is used in these?

I am thinking a Coilcraft or Mini-ciruits impedance matching transformer or a core from an ethernet pulse transformer. Two inches of 32 gauge magnet wire. SMA pig tail. A drop of epoxy.

Would this work?

Leo

That should work. You can experiment with different cores easily and see how they measure up. Ed

Hi all,
In addition to the obvious current transformer, there’s likely to be a balun, to make the probe less sensitive to electric (capacitive) coupling.
Thats’ probably in the longer tail, away from the hole where the wire goes through.

Cheers
David K

Yup, a balun (CM choke) could be in the rather long section of the mechanical mounting structure between the small core and the cable connection. It would help with CMRR.

I have successfully made a CT-6 replacement by taking apart an ethernet transformer (Bourns SM51108), cutting off the old windings and winding 10 turns of thin wire on the toroid.
This transformer model is not moulded, coils are just glued to the inside of the empty tub shell.

After testing it with 50mV source in series with 50R load (1mA primary current) I got exactly 5mV/mA response on the secondary into a 50R load (SA or RF voltmeter.) BW is from 70kHz (-3dB) to 2GHz+.

Still, if there is anyone in the UK who has original Tek CT-6 I'd like to borrow it for a few days to X-ray it.

Leo

Ed, David, thank you for the CM choke reminder.
I needed this for 10MHz sinewave but it's a good idea to keep things tidy at the higher end.
Leo

Leo: More than that, the very wideband CTs us distributed wdgs and terms and low perm GHz material.

see the excellent Tektronic Circuits Concepts



Oscilloscope Probe circuits



Probe Measuremens



Jon