Lou, It turns out not to be that critical. The ambient generator is a LOT further away, so about all that changes is amplitude. And often you don't need _complete_ cancellation, just 10 or 20 dB. Example: broadband noise from a nearby TV video signal can mess up a front-end. Cutting it 10 dB is often all it takes to be able to see "below" the limit.
Tedious? Yes. But if one must measure emissions in the presence of on-frequency or nearby ambients, then tedious is the BEST we can do! And if SA with the system installed meets their requirement, the FCC could approve it. Just has to be demonstrated to the Commission's satisfaction. Not trivial! Cheers, Cortland ====================== Original Message Follows ==================== >> Date: 08-May-99 06:39:18 MsgID: 1068-10160 ToID: 72146,373 From: Lou Gnecco >INTERNET:[email protected] Subj: Re: Phase cancellation Chrg: $0.00 Imp: Norm Sens: Std Receipt: No Parts: 1 Cortland: I wonder how well that cancellation system works as you move the receive antenna up and down the hoist, and as you rotate its polarization. You would have to re-adjust the cancellation system every step of the way. This sounds like a lot of work. It would be simpler to run the test at night or on a weekend when the most troublesome ambients are usually down. If you don't keep tweaking it just right, it seems to me that the cancelling signal could actually make the problem worse. A system like this makes testing much more complicated. When you make a test more complicated, the probability of human error goes way up. I think you are going to have to wait a long time for the FCC to buy off on this, if ever, and as for the europeans? forget it! Lou At 11:19 PM 5/7/99 -0400, you wrote: >We had the benefit of a fairly simple, flat environment, both at the (now >closed) Fountain Valley location and the main OATS in Irvine. It was >possible to put a bicon in an area where almost every ambient could be >canceled, but tedious in the extreme, because the location was peculiar to >each ambient. > >Using a delay line and variable gain/attenuation, and careful siting of the >ambient antenna, seems to me appropriate for _most_ OATS except those in >hilly country - and those generally are there because of the low ambients. > >by the way, this is NOT a new idea; indeed, I believe there have been >Papers in the IEEE EMC Proceedings on this kind of a a setup. The >stumbling block seems to have been FCC reluctance to approve a non-standard >setup. But if SA were taken with an ambient canceler going, it seems to me >that would effectively demonstrate equivalence. > >Cortland > >Cortland > >====================== Original Message Follows ==================== > > >> Date: 07-May-99 10:05:24 MsgID: 1068-8273 ToID: 72146,373 >From: "Brent DeWitt" >INTERNET:[email protected] >Subj: Phase cancellation >Chrg: $0.00 Imp: Norm Sens: Std Receipt: No Parts: 1 > > >I have also played with phase cancellation, and found one very serious >limitation, multipath. Unless you are out in a situation where the >ambients >look pretty much like point sources, you will be limited in the depth of >the >null that you can create, since you can only cancel one phase front with >one >"reference" antenna. Since many folks build sites in the hills, mountains >or gullies to try to avoid ambients, this puts the site in a worst case >location for using phase cancellation. > >Maybe in Topeka......... > >Best regards, > >Brent DeWitt > >====================== 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). > --------- 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).
