K4SAV wrote:
>The thing that surprised me when looking at the designs others have
>done was that many people used the clamp-on ferrites that are intended
>for RFI suppression. These add a large series impedance into what you
>are trying to measure and will mess up the current you are trying to
>measure.
It is important to terminate the secondary winding with a low-value
resistor. If you do, then even an RFI suppression bead will act as a
transformer with a very low insertion impedance in the main line. For
example, if a 10-turn secondary is terminated in 47 ohms, the insertion
impedance in the main line is theoretically 0.47 ohms; and in practice
it is only a few ohms.
If you leave the secondary with a high-impedance load, *then* you will
see the full insertion impedance of the ferrite bead. (A simple
impedance meter like the MFJ-259B will show this effect quite well.)
--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek
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