[time-nuts] Re: Dual Supplies for Low Offset Phase Noise Analyzer

[Lux, Jim]

On 7/14/22 4:49 PM, Chris Caudle via time-nuts wrote:
> On Thu, July 14, 2022 2:15 pm, Lux, Jim via time-nuts wrote:
>> I like the rectangular boxes made from an extrusion, with covers.
> How do those boxes work for low and mid frequency shielding?  Does the
> aluminum oxide that grows on bare aluminum keep the side extrusions and
> plates you add to make a box from making good electrical contact?

They are iridited or otherwise chemical conversion processed (aka 
chem-film) so the surface is conductive.

https://www.cpiaero.com/s/compac_catalog_2018.pdf which seems to map to 
this:

https://static1.squarespace.com/static/5f99d7019f16e4208b2969ac/t/5fe21d074b969b4e07f20066/1608654089673/compac_catalog_2018.pdf

"... finish chemical film per MIL C 5541, Class 3, conformance to MIL 
45208A "

> I assume that at GHz frequencies the oxide is thin enough that you get
> capacitive coupling, but that doesn't seem reliable at 10MHz, and
> especially not for power line protective earth connection if you put a
> power supply inside the box.
> I like aluminum because it is easy to drill, but I've always been nervous
> about relying on it for electrical connections because of that oxide
> coating.

chem film is your friend. Inexpensive, standard process, etc.

True, the inside of your drilled hole is bare aluminum and instantly 
oxidizes.