If you set up a second antenna, at a much greater distance than your EUT from the measurement antenna, and combine the signals from the two in the proper phase and amplitude, you can cancel ambients. I have done so with a resistive combiner (two attenuators and a "tee' fitting) and a spare bicon. However, this may often not be worth the trouble, as it cancels only one ambient at a time and one must move and rotate the antenna.
A more sophisticated setup would use a slotted line with longer line sections switched in or out, and a variable attenuator on the "ambient" antenna. I once started to build one of these, but ambients at my location were not bad enough to warrant the work. Cortland ====================== Original Message Follows ==================== >> Date: 06-May-99 08:36:19 MsgID: 1068-5104 ToID: 72146,373 From: "Aschenberg, Mat" >INTERNET:[email protected] Subj: RE: Precompliance Testing Chrg: $0.00 Imp: Norm Sens: Std Receipt: No Parts: 1 What would that method be? Mat > -----Original Message----- > From: Gorodetsky, Vitaly [SMTP:[email protected]] > Sent: Wednesday, May 05, 1999 6:22 PM > To: 'Flinders, Randall'; 'Hans Mellberg'; 'emc-pstc' > Subject: RE: Precompliance Testing > > In stationary case, such as OATS, there's a relatively inexpensive way of > automatic cancelling ambients out . > > -----Original Message----- > From: [email protected] > [SMTP:[email protected]] > Sent: Wednesday, May 05, 1999 12:23 PM > To: 'Hans Mellberg'; 'emc-pstc' > Subject: RE: Precompliance Testing > > I second that opinion. My experience shows SEVERE ambient issues > with rooftop sites. > -- > Sincerely, > > Randall T. Flinders > EMC Engineer > Emulex Network Systems > V: (714) 513-8012 > F: (714) 513-8265 > [email protected] > ______ ______ > ______\ /______ > ______/ \______ > E M U L E X > > Chairman > Orange County Chapter > IEEE EMC Society > [email protected] > > > > ---------- > From: Hans Mellberg > Sent: Wednesday, May 05, 1999 7:59 AM > To: [email protected]; [email protected]; > Gary McInturff > Cc: 'Brent DeWitt'; Allen Tudor; [email protected] > Subject: Re: Precompliance Testing > > > > Before you put a rooftop OATS, (assuming you are not located > in Easter > Island or the Caribean Islands!) you are going to deal with > substantially higher ambient signals. It so happens that > when you need > a stronger signal, a common practice is to raise the > antenna! I have > battled those problems twice in my past and I would not > reccomend > rooftop OATS anymore. > > > --- [email protected] wrote: > > May I add a note of caution: > > It may be worthwhile to check the permissible > > loading of the roof, especially > > when you are in the Southwest where roofs are mostly > > for shade and a few drops > > of rain. I guess that you don't want to appear > > suddenly in the conference room > > below.... > > Bogdan. > > > > Gary McInturff wrote: > > > > > I'll agree with Brent, and others, the headaches > > of a metal room or the > > > metal studs et al, in a building are going to make > > you pull your hair out. > > > But there is an alternative to the parking lot. > > You may want to consider the > > > roof. The ground reference can be put up there as > > well, especially if you > > > are doing pre-compliance stuff. You don't have to > > give up parking space - > > > which is sure to irate somebody. The roof gets a > > little hot, but that only > > > gives you the opportunity to work in your cutoffs, > > and showing up to a > > > meeting with the suits dressed like this is always > > good for a laugh! > > > Gary > snip > > === > Best Regards > Hans Mellberg > EMC Consultant > _________________________________________________________ > Do You Yahoo!? > Get your free @yahoo.com address at http://mail.yahoo.com > > > --------- > 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).
