________________________________
From: [email protected] [mailto:[email protected]] On Behalf Of Price,
Andrew
(SELEX GALILEO, UK)
Sent: Wednesday, July 29, 2009 4:43 AM
To: [email protected]
Subject: Mil-Std-461F 41" rod Ferrite & Cable query?
Hi all.
A question regarding Mil-Std-461F for the mil experts.
What ferrite is recomended for the cable from the 41" Rod to the bonded
elbow?
What is the prefered cable i.e. RG59/U, RG58C/U (both used for BNC
cables or
RG214/U often used for N type cables)?
Regards
Andy
Andrew P. Price
Principle Hardware Engineer, EMC Specialist
SELEX GALILEO, Sensors & Airborne Systems
Christopher Martin Road
Basildon
Essex SS14 3EL
Mail Ref : K160
Andy:
I can't answer that, as I haven't done an "F" level RE102 yet. However, since
the whole point is to affect RF surface currents on the coax below 30 MHz, it
should be a large mass of ferrite. Think a tube rather than a bead. Also, the
ID of the ferrite should be as closely matched to the OD of the cable as
reasonably possible. Think a nice slip fit instead of a sloppy collar. My
choice would be a cylinder, maybe .3" ID by .7" OD by 1.5" long. I'll be very
interested in anyone's views about ferrite material selection, and if anyone
wants to recommend a specific part number.
For the cable, I use RG-223A/U. This cable has an OD of 5.4mm, has two shields
of silver plated copper (each with 95% coverage) and a silver-plated copper
center conductor. It's completely excellent for use up through 30 MHz, and I
normally use it to 1000 MHz (unless I need every dB of sensitivity I can get).
For instance, I use a 20' length connected to a 10' length by a bulkhead
feedthrough fitting, and this combination has 1 dB loss at 30 MHz and 6 dB
loss at 1000 MHz. This cable is flexible, but holds up to daily use very well.
(Use good quality compression coax connectors.) Buy a 500 foot roll and make
your own cables.
Don't use RG-59, because it is 75 Ohm cable. Don't use RG-58, even the best
RG-58C is still a single braid jacket and has higher loss and lower shielding
effectiveness. It's just not worth having RG-58 in your lab when you should
use all RG-223 instead.
You can use RG-214, but it's overkill for RE102. You don't need it's power
ability, and it's mass and lower flexibility tends to strain BNC connectors.
My choice for extremely low-loss coax for emission testing (that is, very low
power in the coax) is United Microwave Type AA-190. This cable is about 0.2"
OD, mechanically delicate and uses factory-installed SMA connectors. However,
it has superb low loss; my 30' length has 2.7 dB at 1 GHz and 12 dB at 18 GHz.
Storm and Gore make mechanically better cable, but the UMW cable only costs
around $300 (last time I bought one). (I have a 20 foot Gore cable that cost
$2,000, a long time ago!)
Ed Price
[email protected] <blocked::mailto:[email protected]> WB6WSN
NARTE Certified EMC Engineer
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA USA
858-505-2780
Military & Avionics EMC Is Our Specialty
-
This message is from the IEEE Product Safety Engineering Society emc-pstc
discussion list. To post a message to the list, send your e-mail to
<[email protected]>
All emc-pstc postings are archived and searchable on the web at
http://www.ieeecommunities.org/emc-pstc
Graphics (in well-used formats), large files, etc. can be posted to that URL.
Website: http://www.ieee-pses.org/
Instructions: http://listserv.ieee.org/request/user-guide.html
List rules: http://www.ieee-pses.org/listrules.html
For help, send mail to the list administrators:
Scott Douglas <[email protected]>
Mike Cantwell <[email protected]>
For policy questions, send mail to:
Jim Bacher <[email protected]>
David Heald <[email protected]>
