The effectiveness of magnetic shielding increases dramatically with metal
thickness so you are headed in the right direction.
Gary
> On Jun 8, 2017, at 12:40 AM, Josh Gibbs <gibbsjj@gmail.com> wrote:
>
> 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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