A company I used to work for had a rooftop OATS in the mid 80's in SW Michigan. Even at 3 meter distance, the ambients were so high it was almost impossible to do a Class B scan. If you knew of a problem frequency, you could use it for troubleshooting. I hope you are in a remote area were your ambients are not too bad. I'm sure you have done some pre-testing to make sure it is worth doing.
We ended up building an Oats in a gravel pit about 20 miles away. It was great when we first built it and it is currently still in use by another company, but with all the wireless devices around and cell phones, the ambient is not nearly as clean as it once was. For those who have the money, build a chamber. Or find yourself someplace close by where you can get your testing done. For a ground plane we used some kind of heavy gauge wire mesh. The openings were less than 1/4". We tried to wield the sections of mesh together but ended up using aluminum strips with small bolts to squeeze the overlapping mesh together. This worked good but in the winter it was very hard to shovel snow off of for the shovel kept catching on the mesh. But wire mesh was a very inexpensive way to create a ground plane. On another ground plane we did which cost much more, we laid out a deck make from treated wood. I covered the deck with sheets of aluminum. Where the sheets butted up against each other, we used 16" wide aluminum flashing under under the joints, then screwed the sheets every two inched along the edges through the flashing and into the treated wood. A few more screws in the middle of each sheet kept it from buckling (it still buckeled a little). This gave us a nice smooth ground plane. We had a local company pre drill the screw holes (recessed) in the aluminum sheets (strippet machine). About every couple years we remove the screws, clean up the sheets with a floor buffer, put down new flashing and screw it all back down (offset slightly so the screws go into good wood. (We use stainless steel deck screws). Its a bit of work but that way we know we are getting a good connection between the sheets. We've thought about wielding the aluminum sheets, but what we do seems to work ok. Good luck in your project. The Other Brian From: [email protected] [mailto:[email protected]] On Behalf Of John Woodgate Sent: Tuesday, December 11, 2007 12:21 PM To: [email protected] Subject: Re: A question regarding OATS setup In message <[email protected]>, dated Tue, 11 Dec 2007, [email protected] writes: >We are considering placing an OATS on the roof top of a building for >some inhouse testing. Does anyone have any experince with OATS on roof >tops? They do exist. >To our lab we may be required to run 60' of cable from our antenna. >Does 60' sound too long? At 1 GHz, 6' is 'long'! Thinks again; you need a mini-lab (plastic dome) on the roof. >We would like to get good site attenuation out to 1GHz. Also any >suggestions on material for the ground plane would be appreaciated. >Since we will be running the grounding conductors before we can test >the site, we wonder if we should provide more than one ground >connection to the plane. Not sure what you mean by 'ground connection'. Any wire from a rooftop plane to the planet's surface is long enough to be an inductor of very significant impedance, and at 1 GHz it's a transmission line. You had better regard your 'ground plane' as a counterpoise to any common-mode emissions and ground it only for protection against lightning, i.e. with a lightning conductor. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk For very important information, please turn over. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc LECO Corporation Notice: This communication may contain confidential information intended for the named recipient(s) only. If you received this by mistake, please destroy it and notify us of the error. Thank you. - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
