“In addition, Figure RE102-6 is revised to show the antenna lowered so that the center point of the 41” rod element is 120 cm above the test chamber floor. Further, this figure shows that the coaxial cable emanating from the rod antenna base is carried directly to the floor and grounded there, with a ferrite bead installed between the rod base and the floor ground point. The ferrite bead should have between 20 – 30 Ohms impedance at 20 MHz. A bead that works in this application is the Ferrishield B1642.”
>From an article in Conformity magazine that describe the –461F changes, January 2008. Ken Javor Phone: (256) 650-5261 ________________________________ From: "Price, Edward" <[email protected]> List-Post: [email protected] List-Post: [email protected] List-Post: [email protected] Date: Wed, 29 Jul 2009 05:52:54 -0700 To: "Price, Andrew (SELEX GALILEO, UK)" <[email protected]>, <[email protected]> Conversation: Mil-Std-461F 41" rod Ferrite & Cable query? Subject: RE: Mil-Std-461F 41" rod Ferrite & Cable query? ________________________________ 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]> - 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]>
