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: rbon...@orionscientific.com 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 majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
