It's a commonly known problem for NiZn ferrites. Whether a mag mount antenna yields sufficient field to cause the problem is a different question.
For specific literature cites: Fair-Rite: "Strong magnetic fields or excessive mechanical stresses may result in irreversible changes in permeability and losses" http://www.fair-rite.com/newfair/materials67.htm EPCOS: www.acaltechnology.com/download.php?id=111034 "NiZn-materials. The magnetic properties of NiZn-materials can change irreversible in high magnetic fields." Jack K8ZOA Ron D'Eau Claire wrote: > Gentlemen, I'd appreciate a link to any manufacturer's or engineering data > you have, since I have never seen a ferrite or powdered iron core that was > permanently affected by a magnet, nor have I ever encountered any > manufacturer's warnings about magnets around modern electronics in the > equipment I've worked on over the years. > > My hardware experience includes repairing aircraft navigation and radio > equipment, broadcast transmitters, mobile radio equipment from HF through > UHF and repairing and certifying all sorts of communications gear from MF/HF > radios to satellite systems, radars, GPS and other navigational equipment on > ships of all sizes from fishing vessels to some of the largest deep water > vessels afloat. > > Much of this gear protects lives, and I've always been careful to do > everything *by the book* per the manufacturer's instructions and the > regulations. > > It is true that magnets can affect cores by detuning circuits to some extent > *while the magnet is present*. Indeed, some systems use a permanent magnet > brought near a toroid, or a separate winding through which a d-c current is > passed to create a magnetic field, to 'tune' the circuit by adjusting the > inductance slightly. > > Those systems for adjusting the inductance work because the toroid is not > permanently affected by the magnetic field. > > Several years ago a number of Elecraft K2 owners noted the speaker magnet in > the top cover affected some alignments. The solution was to be sure the > cover was in place first so the field from the powerful speaker magnet was > in position just as it would be in normal operation. There are no problems > caused by the presence of the magnetic unless it is moved. > > The only thing I can suggest about the guy with the 2-meter rig that was > permanently "detuned" by putting mag-mount antenna on the case is that it > magnetized the case itself and the permanent magnetic field resulting from > the case affected some nearby toriods. Demagnetizing the case should fix the > problem. > > When I worked in land mobile in the 1980's, people often did exactly that to > set up a temporary "demo" installation of 700 or 900 MHz radios without any > deleterious effects on their performance. > > I used to warn against that, not because of the magnet, but because of the > very close proximity of the operator to 35 watts of 700 or 900 MHz energy > from that antenna when transmitting. > > I'd suggest Hams avoid doing that for the same reason unless they're keeping > the transmit power very low, even on bands as low as 144 or 50 MHz. > > Ron AC7AC > > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
