Kevin, how to account for the ground plane? I believe that if you have raised the RX antenna for maximum signal (above 100 MHz anyway) the plane will give a 6 dB increase over the free-space electric field. To confirm this I would use NEC and run a simple dipole-to-dipole simulation with and without the plane. One in free space and one over ground. In the simulation you must account for the change in TX power as the TX dipole impedance changes with and without the ground plane. But, isn't this included in the NSA? Here is a link to a program that quickly calculates theoretical NSA: http://www.emctest.com/downloadabletools.cfm Others: Please comment on any mistakes I may have made so that Kevin isn't sent off on a tangent. Thanks. Dave Cuthbert Micron Technology
From: [email protected] [mailto:[email protected]]On Behalf Of Kevin Harris Sent: Friday, January 09, 2004 9:34 AM To: EMC-PSTC ([email protected]) Subject: Measuring Radio Power on an OATS Sages, I have a question concerning converting measured field strength to EUT output power on an OATS. >From the Canadian standard for radio test methods (RSS 212) there is the following quote "The following formula may be used to convert the maximum field strength (FS) in volts/metre to the EUT output power (TP) in watts: TP = (FS x D)2 30 x G where D is the distance in metres between the two antennas and G is the EUT antenna numerical gain referenced to isotropic gain. (Note: In an open area test measurement the effect due to the metal ground reflecting plane should be subtracted from the maximum field strength value in order to reference it to free space, before calculating TP)." My question comes from the note. How do I determine the effect from the ground plane. Should I just assume that a maximized peak always contains the effect of a perfectly in phase reflection from the ground plane or is there a method of determining the actual effect ( short of covering the ground plane in anechoic material :) ) ? As far as I'm aware I've never had a lab correct for this, nor have I seen anything in the few other radio standards I use mention this. Is it ( as I suspect ) the common practice that the raw measurement is always used in the calculation and no attempt is made at the ground plane correction. Kind Regards, Kevin Harris Manager, Approvals and CAD Services Digital Security Controls 3301 Langstaff Road Concord, Ontario CANADA L4K 4L2 Tel: +1 905 760 3000 Ext. 2378 Fax +1 905 760 3020 Email: [email protected]
