Moving the EUT is usually impossible, as it is fixed to the OATS. Moving the ambient antenna changes the phase of the ambient signal it receives relative to the measurement antenna; rotating it changes amplitude and polarity. By the right choice of position and orientation, an ambient may be much reduced at the summing point. If the ambient antenna is much farther form the EUT than the measurement antenna, it will have little effect on the measurement. Some care shod be taken to prevent measured emissions from being sent to the ambient antenna and ambient signals to the measurement antenna.
A more "elegant" way to adjust phase and amplitude on the ambient leg is with a delay line and attenuator. Absolute accuracy isn't needed, just consistency. It also keeps the operator out of the rain. Not a trivial consideration for REAL open air sites. Cortland ====================== Original Message Follows ==================== >> Date: 07-May-99 08:37:22 MsgID: 1068-7917 ToID: 72146,373 From: "Aschenberg, Mat" >INTERNET:[email protected] Subj: RE: Precompliance Testing Chrg: $0.00 Imp: Norm Sens: Std Receipt: No Parts: 1 Why must you move the antenna, and not the unit? 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 > -----Original Message----- > From: Cortland Richmond [SMTP:[email protected]] > Sent: Friday, May 07, 1999 9:21 AM > To: Aschenberg, Mat; ieee pstc list > Subject: RE: Precompliance Testing > > 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 ===================== ====================== 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).
