John Harrington wrote: >> I'm having some fun with an NSA measurement. I get a swing of 8dB between 30MHz and 45MHz horizontally polarized. At 30 MHz I get too little attenuation (i.e. I receive too much of the transmitted signal) and at 45MHz too much attenuation. The rest of the frequency range is good within +/-2dB and the Vertical polarization is good at all frequencies.
Are there any OATS Gurus out there who could shed some light on this or at least suggest an illuminating text? << 10 meters or 3? At the low end, mutual coupling between dipoles affects the measurement on 3 meter sites. See the cover article in the Spring 1992 issue of Compliance Engineering magazine, "Site Attenuation: The New Rules for OATS" by Isidor Strauss. Corrections can be up to 4 dB. Adding ferrites to coax at the antenna *will* help remedy imbalance if the baluns are a problem, but read on; that's not the only thing this detects. If ferrites help, you may have another problem: I once got emissions down on a computer by putting ferrites on coax at the antenna. The lab (correctly) wouldn't accept that, but in the end, they moved OATS AC power wires to a different conduit; RF present on the EUT power cable was being coupled onto the coax that ran next to it. Cortland This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
