[amsat-bb] Ferrite RFI filters and Traps?

[Robert Bruninga]

I cut the RFI Ferrite blobs off of all trash Keyboards and stuff.  These
are great Ferrite devices.



But what are they best for?  IE, 1) are they intentionally lossy or are
they High Q?  and 2) What is their Optimium Frequency range (all ferrite
torroid coil forms come in a variety of materials optimized for different
frequency ranges.  There is a big difference between the ferrite in a
switching power supply (100 kHz) and something usable at VHF or UHF.



I assume these ferrite tubes are probably optimized for digital and power
supply hash only and so probably only suitable for use at HF, but probably
not at VHF and UHF?  And what is their Q?  Can they be used for making high
Q circuits?



Today I am using some on the outside of a coax right at the edge of a
cubesat to decouple the coax going to the network analyzer from the RF
enveolope of the spaceframe for antenna tuning.  So today's question had to
do with their ability to serve as a high loss filter at UHF.



But we may as well list all we know about these ferrites for other
applications?



p.s.  My method for getting them out of the molded rubber is to cut the
cable right clean at the ends.  Then  use a large drill (1/4") to drill out
all the internal wires.  Then use a hacksaw to cut off one end of the
rubber as close as possible to the ferrite but without cutting it.  Then
pealing back the rubber or nibbling at it with a pair of dikes....  Got a
hobby drawer full now.



Bob, WB4APR