Antenna for EMC testing 5

[Scott543]

Hello all. I would appreciate your help with an antenna question. I am a not a serious radio guy, but I am the closest thing to that on our project team. I have been tasked with doing some pre-EMC testing and need help selecting the correct antenna(s).

We need to test some materials for EMI attenuation rate, then assemble the materials and check the EMI attenuation inside the assembly. The test assembly can be of a reasonable size to house the spectrum analyzer and the antenna.

The testing needs to check EMI attenuation from 100 kHz to 1 GHz. I am hoping that there would be one directional-type antenna that would cover that range, but I'm having a difficult time finding a match.

So, I'm hoping there is an expert in this group who would be willing to give me some advice. Can you help by suggesting what antenna(s) I need to conduct the test? I need to know antennas for both the transmit and receive side.

Thanks in advance,

Scott

 

[IRstuff]

Perhaps you can talk to these guys?

http://www.com-power.com/antennas.html

TTFN
faq731-376

 

[VEBill]

"... from 100 kHz to 1 GHz. I am hoping that there would be one directional-type antenna that would cover that range..."

Typically one would need a collection of E3 antennas to cover that sort range.

To answer the next obvious question, by referencing the "Antenna Factor" data included with a calibrated E3 antenna, one may translate the measured signal level into actual field strength.

 

[Scott543]

Thanks, VE1BLL. That is very helpful.

 

[Higgler]

directional at 0.1 Mhz is a huge antenna. You won't find a directional antenna, law of physics. AHSystems has the frequency you need

http://www.ahsystems.com/catalog/currentprobes.php

 

[VEBill]

Exception to the rule: Ferrite 'Loop-stick' antennas can cover 0.1 MHz, and are directional (cardioid pattern with a lovely null). Used for MF-DF systems.

But I don't believe that they make very good EMC antennas. And certainly not for transmit mode!

 

[Higgler]

If I were making a Pre-EMC Test, I'd make my own antenna. Assuming you have a box radiating problem, just a coax. center conductor poking out of the cable may be adequate. Let the length of the center conductor be extended by adding a spool of wire, or maybe wrap wire around a ferrite.
The thought is to have a small, thin antenna that you can place close to your leaking box and pick up more energy than getting a larger antenna away from the box.

Placing your box inside another metal box is a good way to "pseudo amplify" any leakage from your box. Place your hand-made antenna sniffer inside the home made metal box and you can measure leakage more readily.

 

[biff44]

Precompliance testing is done to assure, to a reasonable level, that you will pass the EMI leakage testing if you send the unit to a calibrated test lab (and spend lots of money doing so). So you not only need an antenna that covers your frequency range, you need one that is "calibrated"--usually meaning you have to buy a new one. Ones you find on ebay are sometimes junk, and their initial published calibrations are no longer to be trusted.

Here are some ideas:
3103 conical log spiral, or 3143B Biconilogic antenna.

http://www.ets-lindgren.com/DefenseAntennas

If you do not have the bux to buy one of these, I would get a cheapo discone antenna, like:

http://www.ebay.com/itm/DISCONE-BRO...pt=US_Radio_Comm_Antennas&hash=item2c6898057d

And when you find a spur that seems close to failing your leakage level, double check the level with a quarterwave monopole over a ground plane (sma connector soldered to a FR4 pcb ground plane in the middle, and a length of stiff wire long enough to resonate at that one frequency. You know the theoretical gain of such an antenna.

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting