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Re: [RFI] Solar panel RFI

To: rfi@contesting.com
Subject: Re: [RFI] Solar panel RFI
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Sun, 20 Feb 2022 12:28:00 -0800
List-post: <mailto:rfi@contesting.com>
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

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