One of the many great companies found in the Hudson Valley of New York is Fair-Rite Products Corp. This Wallkill, NY based company specializes in ferrite based products and has been in existence since 1952. You can read about the company history here.
Ferrites are used in almost all electronic devices and are especially useful within the amateur radio community when it comes to building various filtering circuits or for helping to eliminate different types of RFI or radio frequency interference.
The topic of ferrites and applications is far too vast to cover in one article, but Fair-Rite has some great technical notes and other content on its website.
Here is a latest video thanks to Bruce N2KTV who works for this important company. Bruce covers in less than 5 minutes, the theory behind low pass filters, design discussion and a perfect demonstration of a 7 MHz low pass ferrite filter along with how to test it with a very inexpensive tiny spectrum analyzer, which has proved very popular since its introduction about two years ago.