James:
Thats certainly a possibility. I envy your rotational accuracy. I used a tripod head that had 30 bumps around the pan head lock, so each bump was 12 degrees / bump. I tried to align in the center of each bump, but I doubt I got +/- 2 degree accuracy. I did find that my variations were mostly from slight perturbations of the coax system as I rotated the EUT antenna. Despite several clamp-on ferrite tubes, slight displacements of the coax could still easily make a dB of error. And I had to remove the tilt head handle, since it was a conductive tube sticking out horizontally. Ed Price El Cajon, CA USA From: Pawson, James [mailto:james.paw...@echostar.com] Sent: Wednesday, February 29, 2012 2:28 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Antenna Pattern for 2.4 GHz and 5GHz Hi Ed, I've been making antenna pattern measurements recently in our chamber and I too see a variation as you described. One theory I'm working on is that our turntable might not be as accurate in it's 5º increments as it could be. If the set point has a tolerance of 1-2º and that lies on the relatively "steep" side of a lobe then you might expect a large variation for a relatively small positional change. With regards, James James Pawson Leading Hardware Engineer - EMC EchoStar Europe _____ From: Ed Price [mailto:edpr...@cox.net] Sent: 25 February 2012 09:26 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Antenna Pattern for 2.4 GHz and 5GHz If you took a reference level at the start of a 180-degree rotation, after stepping 180 degrees CW, then 360 degrees CCW and then 180 degrees CW, sometimes you could go back to the original point and get a new level that was less than 0.5 dB different. And sometimes the level had changed 2 dB, so you got to repeat the test. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ 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 <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ 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 <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
