Spectrum Analysis Comparing Gen II vs III

Umm... I've been in a lot of EMC compatibility testing areas. Yeah, there's Faraday cage rooms that have nothing but copper screens and weird metals doors and metal gaskets all over. You can get some basic testing done in those.

However, the much more common EMC rooms look just like audio anechoic chambers. They have all those pyramid-shaped things pointing towards the center of the room from the walls and ceiling; there's usually a metallic floor so one has a ground plane to work from. It's an electromagnetic anechoic chamber, and those pyramid shaped things aren't there to absorb sound - they're there to absorb radio energy. And they're vaguely electrically conductive, the better to turn electromagnetic radiation into heat.

There's also the audio kind. Actually, I've never been in one of those, although I vaguely remember seeing pictures of one. I think (I'm not sure) that the pyramids are (a) bigger, (b) black, and (c) are on the floor, too, pointing up. These things absorb air vibrations.

For better or worse, people call both anechoic chambers. Because, well, you don't get echos in either one. Of whichever waves one is playing with, or course.

They both tend to be audio quiet, although the real audio ones are much quieter, natch.

KBeck.

 

FWIW, in my experience, the RF anechoic chambers were for antenna patterning, when frequencies were high enough that you didn't need an outdoor range. The screen rooms were for radiated-interference qual testing.

And when I DJ'd at the 5-kW directional in the sticks, the booth was lined with egg cartons.

 

Just to clarify this, as someone who has used both screened rooms and anechoic chambers for RF measurements.

If all you want to do is look at emissions from a vehicle, then all you need is a screened room. The ones I've used have varied, from an octagonal one around 50ft across and 40ft high, with full exhaust extraction and inlet air supply, capable of taking a main battle tank weighing around 60 tons, to a 12ft square room used to check radio, radar and nav sub-systems. All had the ability to position sniffer antennae around the object under test, ideally through a full sphere, although for vehicles a hemispherical measurement is more normal. One chamber I've worked in had a turntable for the vehicle and a fibreglass antenna mounting arm hinged to the floor. This allowed a full hemispherical measurement to be made, with the arm incrementing up a set angle for every complete revolution of the vehicle on the turntable.

If you want to do full EMC testing, as distinct from just looking for potential vehicle emitters that may be causing EMI, then you need an anechoic chamber. This will have walls, floor and ceiling lined with RF absorbent material, either carbon loaded foam pyramids or ferrite absorber tiles (usually referred to as RAM, radio, or radar, absorbent material). An anechoic chamber has to be sized for the frequency range of interest, as does the RAM liner. The reason for the RAM lining is that you will be bombarding the object under test with directional RF (for susceptibility testing) and you don't want the RF bouncing around all over the place.

Jeremy

 

We used screened rooms and magnetic shielding. I headed up an engineering department for a major MRI company. You had to keep RF and magnetic fields away from those things, or it messed up the signals. I recall one location near a hospital parking garage, where moving cars caused problems. That one took extra magnetic shielding.

Tom

 

You know the sad thing is more than a few of use could probably detect turning the cabin lights on and off!

Seriously, the spectrum analyzer data is useful but I'd like to suggest the hams might propose some specific frequency bands to examine. I don't have a dog in that fight as my interests lie in a different area.

Bob Wilson

 

Wondering where the data regarding the prior posted analysis are located? Guessing searching the users posts maybe?

For Near Field EMC testing to clarify. There is also Far Field EMC testing.

The specific antenna type is critical as well from my understanding, wideband and highly characterized.

Amazing what's on the market now for the price within the reach of most, i.e. NanoVNA, TinySA, etc.

 

It is a 13 year old thread, it is possible none of the data is still hosted online.

 

This forum has migrated to new applications and hosts multiple times, sometimes cleanly, but sometimes breaking many old links.

In this case, it appears that his naming of a photo album was lost, but the raw images are still available under the 'Media' tab of his Profile page, unfortunately without any remaining captioning:

snijd | PriusChat

This link doesn't automagically open that Media tab, so you will still need to click on it.