Your logic does not conclusively point to the >table< as the problem; it DOES say there is a problem where the table IS. If you were to completely cover the turntable with ground screen, bonding it to the site ground plane at numerous places, it might be that you would STILL see a problem.
If that turned out to be the case, you would want to investigate discontinuities in the ground screen elsewhere which might produce an anomaly. If it turned out not to be the case, then you might want to see if the anomaly is not where the TABLE is, but in the area where the measurement antenna is placed. Another thought occurs that perhaps other wiring -- table motor, table power sources, antenna mast height control -- are carrying RF which is being confused with actual antenna-currents. A similar effect was noted during EMI tests at a lab in SOuthern California; power and coax ran together in a buried duct, and RF on the AC power were coupled to the coax shield, and mistaken for "real" antenna current. Ferrites on either the antenna coax or the power line fixed that. And good luck! Cortland ====================== Original Message Follows ==================== >> Date: 16-Jul-99 14:41:22 MsgID: 1068-126336 ToID: 72146,373 From: "WOODS, RICHARD" >INTERNET:[email protected] Subj: RE: NSA Chrg: $0.00 Imp: Norm Sens: Std Receipt: No Parts: 1 We have a 10m site, but because of high ambients, we calibrate and test at 3m. So, we have a very large ground screen for a 3m site. When we place the transmitter on the table, we fail NSA. When we move the transmitter onto the ground screen we pass. We can place the transmitter to the side of the table on in front of the table as pass. Therefore, I conclude that we are not experiencing reflections from objects near the OATS, nor do we have problems with the screen or its connection to earth. The antenna and cable setup also appears to be correct since we can pass off the table. It appears that our 1.5m table is the only unknown. We did find that the continuity between the ring and the screen (a bolted pressure connection) had deteriorated significantly. That is why we added the copper straps as a more permanent connection method. There are eight short, wide copper straps around the 1.5m table. ---------- From: [email protected] [SMTP:[email protected]] Sent: Friday, July 16, 1999 4:00 PM To: WOODS,RICHARD; "INTERNET[ <[email protected]>]"@anritsu.com Subject: re: NSA Richard, Can you detail your procedure to the conclution: "The problem appears to be the turn table" ? Barry ------------- Original Text From: "WOODS, RICHARD" <[email protected]>, on 7/16/99 12:28 PM: 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 [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators). D --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators). ====================== End of Original Message ===================== --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
