On Fri, Nov 6, 2020 at 04:40 PM, David Eckhardt wrote:
Yes, many use 31 material for this purpose. I've wound many like CM chokes
using red cores, 31, and 43 material. Problem is with the higher ?r
materials, I end up with a virtual tesla coil at the transition of my open
wire feeders and the output of the matching network. Too much inductance.
The red cores I use once wound as the CM chokes measure in the vicinity of
+j1000 or greater, even at 1.8 MHz. The red cores are the correct cores to
use for this purpose. These are also the same core material Amidon offers
in their kits.
Hi Dave,
Maybe the reason you get a high voltage when using higher u materials is that they are working effectively and creating a high impedance to common mode current.
I'm concerned that your choking impedance is mainly reactive as this is not likely to be as effective as a choke with a mainly resistive impedance.
Iron powder is not the correct material to use for this particular purpose, irrespective of who is selling it, and it is not clear from Amidon's website which cores are intended for specific designs which adds to the confusion.
Here are some good references regarding choke Baluns and why highly reactive common mode impedances should be avoided.
Regards,
Martin - G8JNJ
