If the problem is on the horizontals, I hope that you have accounted for the Mutual Impedance Correction Factors of Table G4 (CISPR 16-1:1993).
Also, check and make sure that your 3 metre antenna factors are ok, no VSWR problems (put a 3 dB pad to check). Do also make sure that there is no ambient sitting on 30MHz. If possible, shift the frequency marginally (just to get rid of the standing wave null/peak or standing wave, if any- the idea being to catch the Peak value of the direct and reflected rays) and repeat the test. I would also prefer to use two identical tuned dipole antennae for the test, and not broadband. The way I look at it is, if it was ok for 5 years, it points more to deterioration. Although, I am sure that you have done all this. In my personal opinion (and it is mine only!!), I am against performing the mandated 10 metre tests at say 3 metres or whatever, because of erroneous 3/10 metre correlation particularly in the 30 to (say) 80MHz region due to near field effects ( the 2(D exp 2)/lambda) effect. The correlation is fairly bad if the EUT is large, with dimensions approaching test frequency. If there are any ambient conflicts, I prefer zooming in at a reduced bandwidth (lower than 120kHz, for better resolution) if necessary. Why don't you repeat your 30MHz NSA at 10 metres? Regards Arun Kaore EMC Engineer ADI Limited Systems Group Test & Evaluation Centre Forrester Road, St Marys NSW 2760 P O Box: 315, St Marys NSW 1790 Tel: 61 2 9673 8375 Fax: 61 2 9673 8321 Email: kao...@sg.adi-limited.com.au <mailto:kao...@sg.adi-limited.com.au> -----Original Message----- From: WOODS, RICHARD [SMTP:wo...@sensormatic.com] <mailto:[SMTP:wo...@sensormatic.com]> Sent: Saturday, 17 July, 1999 3:54 To: 'emc-pstc' Subject: NSA Argh! For the first time in five years, our NSA is out of spec on our 3 meter OATS at 30 MHz. The problem appears to be the turn table. We can move the equipment off of the table to one side or toward the front and comply, so it does not appear to be an off site reflection problem. We have replaced marginal brushes from the table to the ring and we have added wide copper ground strips from the ring (attached with screws) to the ground screen (soldered). Still won't pass. Suggestions? --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org <mailto:majord...@ieee.org> with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com <mailto:ed.pr...@cubic.com> , jim_bac...@monarch.com <mailto:jim_bac...@monarch.com> , ri...@sdd.hp.com <mailto:ri...@sdd.hp.com> , or roger.volgst...@compaq.com <mailto:roger.volgst...@compaq.com> (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
