This is an interesting discussion for all who operate a lab. I will like to inject that I have observed that about 1/3 of EMI labs are using ferrites at the base of the antenna connection. This is based on having visited more than 30 labs on 3 continents during the last 15 years. The reasons given are pretty much in line with the comments on this discussion.
- Nathan Belsher Senior EMC Engineer Nortel Research Triangle Park, NC. (919)-991-2769 [email protected] -----Original Message----- From: Brent DeWitt [SMTP:[email protected]] Sent: Thursday, November 12, 1998 10:39 PM To: [email protected] Cc: EMC PSTC mail list Subject: Re: ANSI C63.4 [email protected] wrote: > > The ferrite loaded mast cable is obviously there for common mode rejection. As > such, the CM can only be sourced form unbalanced baluns at the antenna, or > from the imbalanced complex impedance variance caused from the mutual > inductance of the antenae over the ground plane. Or from direct radiation onto the shield, which happens rather noticeably during NSA measurement with the close proximity of the transmit antenna. On a related topic; just for fun, I built a small, battery powered comb generator that attaches directly to the transmit antenna with no cable. This eliminates the companion problem of unbalanced current on the shield of the transmit antenna. It _seems_ to have improved the consistency of measurement by about 0.75dB. From my experience, measurement of NSA is something of an odd duck. There seems to be very little discussion of the problems associated with the transmit side of the equation. I think it would help to open up discussion in this area. Best regards, Brent DeWitt Datex-Ohmeda Medical Louisville, CO --------- 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). --------- 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).
