Thanks Carter. I tried some shielding using some thin steel I had, but I
want to replicate the shield that Ten-Tec used. They must have done that
for a reason!
It turns out that my C21 digital is a very early one - serial number 42. By
the time they were up to ~200 they had started putting in the shields.
I'm going to try replicating the shield with some thicker steel - similar
gauge as the chassis. If that has some positive effect then I might look at
adding some Mu-metal.
73,
-Josh WA7FPV
> Aluminum is non-magnetic, so not sure if it will do what you expect. I
> thought you had to use iron or mu metal (used to shield scope tubes) for
> magnetic shielding. From Wikipedia:
> *Mu-metal* is a nickel <https://en.wikipedia.org/wiki/Nickel>–iron <
> https://en.wikipedia.org/wiki/Iron> soft magnetic alloy <
> https://en.wikipedia.org/wiki/Alloy> with very high permeability <
> https://en.wikipedia.org/wiki/Permeability_%28electromagnetism%29>, which
> is used for shielding sensitive electronic equipment against static or
> low-frequency magnetic fields <https://en.wikipedia.org/wiki
> /Magnetic_field>. It has several compositions. One such composition is
> approximately 77% nickel, 16% iron, 5% copper <
> https://en.wikipedia.org/wiki/Copper> and 2% chromium <
> https://en.wikipedia.org/wiki/Chromium> or molybdenum <
> https://en.wikipedia.org/wiki/Molybdenum>.
>
> The high permeability of mu-metal provides a low reluctance <
> https://en.wikipedia.org/wiki/Reluctance> path for magnetic flux <
> https://en.wikipedia.org/wiki/Magnetic_flux>, leading to its use in
> magnetic shields <https://en.wikipedia.org/wiki/Magnetic_shielding>
> against static or slowly varying magnetic fields. Magnetic shielding made
> with high-permeability alloys like mu-metal works not by blocking magnetic
> fields but by providing a path for the magnetic field lines <
> https://en.wikipedia.org/wiki/Magnetic_field_line> around the shielded
> area. Thus, the best shape for shields is a closed container surrounding
> the shielded space.
>
>
> Uses and properties
>
> Mu-metal is used to shield equipment from magnetic fields. For example:
>
> * Electric power <https://en.wikipedia.org/wiki/Electric_power>
> transformers <https://en.wikipedia.org/wiki/Transformer>, which are
> built with mu-metal shells to prevent them from affecting nearby
> circuitry.
> * Hard disks <https://en.wikipedia.org/wiki/Hard_disk>, which have
> mu-metal backings to the magnets found in the drive to keep the
> magnetic field away from the disk.^[/citation needed
> <https://en.wikipedia.org/wiki/Wikipedia:Citation_needed>/]
> * Cathode-ray tubes <https://en.wikipedia.org/wiki/Cathode-ray_tube>
> used in analogue oscilloscopes
> <https://en.wikipedia.org/wiki/Oscilloscopes>, which have mu-metal
> shields to prevent stray magnetic fields from deflecting the
> electron beam.
>
> 73,
>
> Carter K8VT
>
>
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