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Old 31st May 2020, 11:27 pm   #4
G0HZU_JMR
Dekatron
 
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
Default Re: Faraday chamber.

Neat project! Over the years I've had several attempts to make something similar, but usually much smaller! I didn't have a lot of success unless the box had a decent EMC gasket around the lid faces. Even this didn't work as well as I'd hoped. In the end I bought a used shielded enclosure quite cheaply and it has been brilliant. It uses feedthrough caps for the DC connections although it also has a 9 way D type interface that has feedthroughs built into the connector. It also has several SMA RF connectors.

The feedthrough caps on the dc power feed connections work really well. For comparison, if I try and trap a really skinny wire in via the door seal then this completely compromises the performance.

I haven't tested it properly since I bought it but back then I could put a 32dB gain dual MMIC amp inside the box with a pickup antenna with the output fed to a spectrum analyser. When tested for VHF FM stations or for mobile phone signals the shielding results were amazing as the door was shut and the pressure lock was clicked into place. The signals simply vanished. However, If I repeated the test with a dc power wire trapped in the door rather than being fed in via the feedthroughs the chamber hardly did anything at all. The dc power wire trapped in the door acted as a kind of repeater antenna into the box even though the EMC mesh seal around the door was well squished shut.

The reason I'm telling you all this is that I think you will need to fit some sort of compression EMC seal around the lid edges and you need to use proper feedthrough caps on the dc connections. Otherwise the box may achieve very little in the way of shielding. It might also be worth lining the insides with ferrite and RF absorber. That is what is inside my commercial version although I'm not sure how much this helps.
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Regards, Jeremy G0HZU
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