Hi Bob: I have a couple of questions about your setup:
1) What antenna distance are you using? 2) What antenna are you using? 3) How is the floor treated in your chamber? 4) How often do you perform the calibration? 5) What size is the uniform field area? We regularly run tests above 1 GHz where a single-point calibration is performed just prior to the test, and we typically get repeatability of +/- 5% or better. Erik J. Borgstrom, EMC Engineer, TÜV Product Service, Inc. 1775 Old Highway 8, New Brighton, MN, USA 55112-1891 612-638-0242, fax:612-604-3480, email:[email protected] ------------- Original Text From: "Robert F. Martin ITS/QS-Box" <[email protected]>, on 10/11/97 01:22: To: Internet Gateway@Services@PSNBL["[email protected]" <[email protected]>] Hi Folks! I have been wrestling with a project for a while at frequencies from 1 to 10 GHz. One of our clients is doing tests in this range at field levels of 10V/m, and using the field uniformity restrictions of 1000-4-3. That is, using a planar grid, and showing uniformity of -0,+6dB. We are not using enough power to do the uniformity over the 1.5x1.5m grid, but that is acceptable to the client. (We just do multiple antenna positions.) The real problem is repeatability. Here are some of the stated requirements from the client: - uniformity -0,+6dB over the specified area - second and third harmonic of the test frequency at least 20db below the fundamental - repeatability of +/-0.5 V/m (not dB) - this has to be demonstrated before each test (4-6 weeks apart) (repeatability meaning that using a pre-defined, pre-calibrated generator output, the field level at each position on the measurement grid is +/-0.5 V/m) The test chamber is 16'x24'x13'h and is lined with a hybrid absorber. (i.e.- ferrite tile, as well as 18" carbon loaded cones) We have paid close attention to positioning of the measurement grid, the transmit antenna, the cables, etc. We level on the output power. But..... we can't get to this ideal of 0.5V/m. Has anyone out there been able to demonstrate this kind of repeatability above 1GHz? Has anyone even been ASKED to attempt to follow these guidelines??!! I welcome any input that will either help me resolve the difficulty, or demonstrate that it is out of the range of possibility! Thanks in advance for any advice. Bob Martin, P.E, N.C.E. Sr. Technical Manager ITS- NEBU (978)263-2662 [email protected] The views expressed are my own, and not necessarily those of my employer.
