Imbalance may not be entirely due to an antenna. For example, a site I used in Fountain Valley, California, had a lot of FM broadcast intermod while using a 200-1000 MHz LP. Ferrites on the feed line fixed that; the antenna did not reject common-mode 100 MHz energy on the coax shield, which was then seen as if it were a real signal on the LP. Adding ferrites substantially reduced IM problems at that site.
Cortland ====================== Original Message Follows ==================== >> Date: 12-Nov-98 16:52:15 MsgID: 1065-32688 ToID: 72146,373 From: "WOODS, RICHARD" >INTERNET:[email protected] Subj: RE: ANSI C63.4 Chrg: $0.00 Imp: Norm Sens: Std Receipt: No Parts: 1 Hans, you raised a very good point that needs to be discussed - the need for ferrites on the antenna cable. I have read articles indicating that adding the ferrites when taking NSA measurements was the only way they could make their site compliant. But I have also heard that the reason the ferrites are needed in those cases is that the antenna - most likely a bicon - is poorly balanced. I have also heard that a properly balanced bicon does not need ferrites. Comments anyone? ---------- From: [email protected] [SMTP:[email protected]] Sent: Thursday, November 12, 1998 10:13 AM To: [email protected]; [email protected] Subject: Re: ANSI C63.4 A1. Since concrete is partly conductive and varies with mositure content and ambient conditions, the reflected path with vary substantially. The solution is to place a screen mesh over the top of the concrete. A2. The specified size is that of the elipse which is 2d by root3d. A practical size is 20m by 17m rectangle. A3. running coax on the top surface most likely will not affect the measurements but for NSA measurements, to obtain maximum repeatability ferrite cores are placed every 1m on the mast cable. It would be best to feed the cables diametrically opposed from each other so as to minimize any effects. A4. Theoretically the conrete curbs, the hedges and metal object can cause additional unwanted reflections. Those may or may not be a problem. Metal objects will have the greatest effect since most of the wave will be reflected. Hedges will most likely act as absorbers at certain frequencies, and the curb will cause reflections or absorbtion at certain microwave frequencies. Hans Mellberg EMC Consultant --------- 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). ====================== End of Original Message ===================== --------- 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).
