[RFI] Solar panel RFI

[Jim Brown]

On 2/20/2022 4:13 AM, Hare, Ed, W1RFI wrote:
> The toroids are not marked, so it will not be certain what material they are."

Thanks. For the next Handbook, I've given Ward details of a method to 
identify a few MnZn ferrite materials with an ohmmeter. It was first 
suggested by W1HIS, and I fleshed it out a bit further. It's pretty 
simple. It worked with the three VOMs in my lab -- a Simpson 260, a 
Fluke 8060A, and a nice little no-name digital VOM that I bought for 
about $15 at a northwest Indiana hamfest at least 20 years ago.

With the meter on a high range scale, aggressively scratch the surface 
of the ferrite with the probes so that they get through the coating, and 
note the reading, if there is one. #31, #75, #77, and #78 are MnZn 
mixes, and will show a reading in the range of 100K - 700K; #75, #77, 
and #78 will be in the range of 1K - 10K. #43, #52, and #61 -- are NiZn 
materials, which have MUCH higher bulk resistivities, and will show no 
conductivity at all. These resistivity values, as well as initial 
permeabilty (mu at low frequency) are tabulated in early pages of the 
Fair-Rite catalog.

We're also including methods to zero in on the specific material 
measuring inductance using traditional methods or studying the shape of 
an impedance sweep with a well calibrated Vector Analyzer.

These methods, of course, depend on knowing AL or ui values for the 
various materials. Fair-Rite's published data is FAR more extensive than 
any other manufacturers; others publish little more than marketing or 
limited applications data. For example, Laird (used to be Steward) 
publishes ui values for only two of about eight materials.

73, Jim K9YC