RF transmission testing inside a Faraday cage

Hi ralphjy a while back I did some RF measurements as part of a Molex antenna selection test. I've gathered a few more bits since then like SDR but I noted a homemade anechoic chamber in section 7.1 of my test report: /products/roadtest/rv/roadtest_reviews/400/molex_24ghz_5ghz_ant

The anechoic chamber not only sheilds external RF interfereing with your measurements but it also attenuates internal reflections that would also render your measurements inaccurate.If you can afford it I ponder if the low-cost metal sheds would make an idea starting place. However, RF has a way of sneaking in the very smallest of gaps (depending on wavelenght) and via feed through cables and pipework. Commercial anaechoic chambers as well as screened rooms have metal finger seals around the doors and filtering on the cables/pipes.

The mention of using a local park or field is another great choice if you can work off battery power and if a public space be ready to explain your setup...maybe also to the local law enforcement! A step up would be a boat where you can get away from RF signals and nosey questions plus have a bit of power available, and a fridge for essential test refreshments

I hope you'll have a lot of fun experimenting and learning with BLE and RF. Good luck.

Hi 14rhb,  I took a look at the link in your roadtest and also looked at the first video where he talked about the construction of the RF absorber I Want to Build an RF Anechoic Chamber.

Interesting, but definitely too much work for my project.  And I think my wife would frown on my making a mess molding a bunch of cones - although she is pretty tolerant of my projects .

I took a look at RF absorption material, but even small sheets of it are too expensive to build a reasonable enclosure.  A large field would probably be the best option as you and shabaz have suggested.  I could probably clean out a small metal shed, but it's too bad that absorbing material is so expensive.

I will have fun experimenting and I'm sure that I'll learn something - I already have ...

Hi 14rhb,  I took a look at the link in your roadtest and also looked at the first video where he talked about the construction of the RF absorber I Want to Build an RF Anechoic Chamber.

Interesting, but definitely too much work for my project.  And I think my wife would frown on my making a mess molding a bunch of cones - although she is pretty tolerant of my projects .

I took a look at RF absorption material, but even small sheets of it are too expensive to build a reasonable enclosure.  A large field would probably be the best option as you and shabaz have suggested.  I could probably clean out a small metal shed, but it's too bad that absorbing material is so expensive.

I will have fun experimenting and I'm sure that I'll learn something - I already have ...

It was at the higher end of homemade solutions and definately messy, so good call on giving it a miss. I think it would likely cost quite a lot of money in reality give the price of epoxy and even then the results are uncertain.

I've wondered if lower cost approaches would work. Typical RF anechoic material is a series of pyramids like:

photo source: from Google search => https://www.comsol.com/blogs/modeling-rf-anechoic-chamber-using-periodic-structures

I wonder if a vacuum former would be able to make something like this which could then be spray painted with metalic paint ? Might result in being able to make many panels reasonably cheaply ?

It seems the trick is in using the absorptive material (he was using carbon and graphite).  It would be a fun experiment but I couldn't justify the time and expense to do it.  Maybe if I were designing antennas...

I was thinking absorptive foam (flat sheets) might be good enough for my purposes if I could find something inexpensive to try.

Good point: my idea with metalised surface would just bounce the EM wave down into the valley, I guess at extreme it would then eventually reflect back out?

For low cost approaches: Carbon from lumpwood charcoal perhaps - pulversed in an old blender and mixed with cement? Render it over plasterboard or plywood substrate?

Some commercial materials look like pieces of antistatic foam from IC boxes. Maybe larger sheets of antistatic matting could be used to line a timber framework? https://uk.farnell.com/c/static-control-site-safety-clean-room-products/esd-protection-products/anti-static-mats

Hi! An antenna designer here. Read some very interesting comments on this post. A fully metallic chamber is called as a reverberation chamber and is used to determine the efficiency of the antennas. Anechoic chamber is used for testing the radiation pattern, gain, etc of the antenna. The cost of building an anechoic chamber is very high. We recently got one in my lab and it cost us around 12800 USD and it works only till 18 GHz.
The size of the cone determines the absorption levels and the frequency of the chamber.
Free air testing is also possible for radiation pattern measurements given that there aren't many obstacles in the room so as to minimize the reflections from the objects.