I have seen power cables "impregnated" with ferrite throughout the entire length of the cable. These cables were very expensive (about $20.00 for a 6 foot cable), but were found to be very effective in situations where emissions were seen off of a unit's power cable. These cables were used as a diagnostic tool, but were generally too expensive to ship with a market ready device. However, this does indicate that ferrite along the entire length of the cable would prove effective.
Unfortunately, my experience with these cables was at a former employer, and my memory fails me as to the manufacturer of these cables. It would be interesting to get a hold of some coaxial cable with these properties. Does anyone know of any? Clip-on Ferrites are bulky (and quite heavy). Their repeated use on antenna cables from a day to day perspective is, in my view, quite a hassle, and I welcome any ideas that could provide for a more effective solution. Regards, Randy Flinders EMC Engineer Emulex Network Systems (714) 513-8012 [email protected] ---------- From: [email protected] Sent: Monday, November 16, 1998 8:32 AM To: [email protected]; [email protected]; Robert Bonsen Subject: RE: ANSI C63.4 -- ferrites Bob: You stress the importance of discrete ferrite absorbers placed closely along the antenna cable. The obvious extension of this thought is to have a special antenna coaxial cable which has ferrite material continuously distributed along its external surface. Is this a reasonable extrapolation of the discrete ferrites technique? Or does there have to be at least some spacing between discrete absorptive elements? If a continuous absorptive layer on a coax cable is a good idea, then has anyone ever encountered such a cable? Might there be some practical way to fabricate a flexible "add-on" absorptive sleeve, possibly like the urethane foam thermal barriers placed on water and refrigerant pipes? Regards, Ed ------------------------ From: Robert Bonsen <[email protected]> Subject: RE: ANSI C63.4 -- ferrites Date: Fri, 13 Nov 1998 17:02:52 -0600 To: [email protected], [email protected] > > In my experience when doing testing of semi-anechoic chambers for NSA > performance using ferrites is a must to avoid measurements being influenced > by the vertical drop portion on both the transmit and receive end. Using a > spacing of about half a foot inbetween individual ferrite beads has worked > best for me. Especially in the lower frequencies, up to about 150MHz, the > effect of the cable drop on vertical pol measurements is considerable > (sometimes more than 1.5 dB). Thus, in all the NSA test specifications I > write, I insist on the use of ferrites. > > Of course, not using ferrites on the vertical cable drop allows a chamber > tester to tweak the cables such that at a specific problem frequency the > vertical cable drop portion acts as a reflector to reduce or increase the > transmitted/received signal levels somewhat. This may bring a chamber/OATS > in spec which really isn't. Or bring it out if the tester is not aware of > the problem. > > For better repeatability and better NSA measurements, ferrites are > required. They do not make the cable totally RF-invisible but do > considerably reduce the influence of the cable on the measurements. > > Regards, > -Robert > > Robert Bonsen > Principal Consultant > Orion Scientific > email: [email protected] > URL: http://www.orionscientific.com > phone: (512) 347 7393; FAX: (512) 328 9240 > > > --------- > This message is coming from the emc-pstc discussion list. > To cancel your subscription, send mail to [email protected] > with the single line: "unsubscribe emc-pstc" (without the > quotes). For help, send mail to [email protected], > [email protected], [email protected], or > [email protected] (the list administrators). > > ---------------End of Original Message----------------- -------------------------- Ed Price [email protected] Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA. USA 619-505-2780 List-Post: [email protected] Date: 11/16/1998 Time: 08:32:01 -------------------------- --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
