[Elecraft] K3/100 kit

[Jack Smith]

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
>
>
>
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