From: Ken Javor [mailto:ken.ja...@emccompliance.com]
Sent: Monday, January 29, 2007 6:59 AM
To: emc-p...@ieee.org
Subject: Re: Military RS103 radiated susceptibility testing
No published sources to recommend, but I offer the following observations:
SNIP
4) At 100 V/m, you are pushing a lot of power into the biconical, at least
below 80 MHz. You are likely not achieving 100 V/m below 80 MHz. Instead, you
are driving the amplifier so hard that its harmonic output is close to the
fundamental, and the biconical is so much more efficient with increasing
frequency that the 100 V/m is being achieved at either a second or third
harmonic - the broadband field monitors don't know the difference. The only
way to deal with this is to use longer elements. Then the input impedance at
the fundamental is decreased such that 100 V/m can be established with low
enough power that the harmonics are kept to lower levels than the fundamental.
Such longer elements are commercially available. They will work well in your
application, but unless you have a very tall chamber, they will be difficult
to implement vertically - each individual element is four feet in length.
Ken Javor
Be careful about driving biconicals; be sure the one you are using is rated
for the power you are putting into it! There are various balun designs for
biconicals. Some shouldn't see more than about 0 dBm, while other have such a
"high-power" capability that the balun housing needs perforations for air flow
cooling. (That tells you something about total efficiency.)
Some military tests require illumination to begin as low as 10 kHz, where a
biconical is totally hopeless. There is another antenna design that, although
being relatively inefficient, can produce significant electric fields over the
10 kHz to 200 MHz range. I don't know what to call it, other than an electric
field generator. Of course, it's a transducer, not really a generator, but an
example of the design is the IFI EFG-3 Antenna; see:
http://www.ifi.com/web/html/antennas/antmain.html
You will also want a hefty RF power amplifier; for military work, I would
suggest something on the order of a 1 kW rating. And, with that EFG example,
you also need a 50-ohm termination for the antenna, so that has to be rated
for the amplifier capacity too.
Ed Price
<mailto:ed.pr...@cubic.com> ed.pr...@cubic.com
NARTE Certified EMC Engineer & Technician
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA USA
858-505-2780 (Voice)
858-505-1583 (FAX)
Military & Avionics EMC Is Our Specialty
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