I would try to connect a capacitor from + to the chassis and from - to the chassis to avoid the requirement for shielded cable. Is there a way to make this connection? A 0.1 uF capacitor with short lead is a start. If the total lead+cap length is 1/2 cm the inductance will be about 10 nH. Above 5 MHz this will be dominated by the lead inductance. About +j2 ohms at 30 MHz. Dave Cuthbert
From: [email protected] [mailto:[email protected]] Sent: Thursday, March 25, 2004 3:28 AM To: drcuthbert Cc: [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected] Subject: RE: What is wrong in my 3 meters FAC measurement Dear Dave, Thanks for the detailed reply. You wrote "The bottom line is the common mode RF on the power leads. This needs to be fixed. Bypassing the + and - directly to the chassis at the chassis wall may help." 'By passing' means connecting the + & - of the power supply to the shield of the cable through suitable RC combination near to the EUT? The EUT chasis is of plastic material coated with metal. This metalic coating is not having any electrical connection with the EUT. When the shielded cable was used to power the EUT, d.c negative (digital ground) of the EUT was connected to the shield of the cable to get a pass result. In the power supply d.c negative is connected to chasis earth. Sincerely K.Balasubramanian Sr.Engineer, Hardware. [email protected] 03/25/2004 12:04 AM To: <[email protected]> cc: <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, &! lt;[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <Tajudeen.! [email protected]>, <[email protected]>, < [email protected]>, <[email protected]> Subject: RE: What is wrong in my 3 meters FAC measurement Some more speculation on the FAC measurement: It appears that you have common mode signals on the power cable. At the OATS, when the EUT is connected to GND though the AC powered 12VDC power supply you created a monopole antenna consisting of the power cable (12V cable and the AC power cord of the 12 VDC supply). When the 12V cable is shielded some of the CM current is returned directly to the EUT chassis. You then might have had less CM current on the power supply power cord and less radiation. When using a battery to power things it was all floating, correct? Your "antenna" is now a dipole with the ends being the battery and the EUT. This "antenna" will behave differently than the monopole and could be better or worse, depending on many factors. In the FAC the monopole antenna performance may have dropped due to the lossy "GND". The bottom line is the common mode RF on the power leads. This needs to be fixed. Bypassing the + and - directly to the chassis at the chassis wall may help. Dave From: [email protected] [mailto:[email protected]] Sent: Wednesday, March 24, 2004 7:19 AM To: drcuthbert Cc: [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; ken.ja! [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected] Subject: RE: What is wrong in my 3 meters FAC measurement Dear All, Sorry I think I have not explained properly. FAC Measurements (with shielded or unshielded cable almost the same result) 244.08 MHz 37.5 dB @ 3 meters 162.72 MHz 29.0 dB @ 3 meters 135.60 MHz 24.0 dB @ 3 meters OATS Measurement (unshielded cable used to connect the EUT to the 12 volts d.c. power supply) 244.08 MHz 37.1 dB @ 10 meters 162.72 MHz 31.1 dB @ 10 meters 135.60 MHz 27.2 dB @ 10 meters Some more trials we did in the OATS. By conneting the EUT to the 12 volts d.c power supply using a shielded cable we passed comfortably. While we tested by using a 12 volts battery even without the shielded cable EUT comfortably passed Class B limits. But in the FAC there was no difference found between a shielded cable and an unshielded cable. Now the question is what was the reason for the failure at OATS. The power supply? The cable? The combination of power supply and cable? Anything else? Sincerely K.Balasubramanian Sr.Engineer, Hardware. [email protected] 03/23/2004 01:37 AM To: <[email protected]>, <[email protected]> cc: <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, &! lt;[email protected]>! , <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <T! om_Cokenias_tom@tncokenias.! org>, <[email protected]>, < [email protected]> Subject: RE: What is wrong in my 3 meters FAC measurement Are the measurements in dBuV/m at 3 meters and at 10 meters? Dave Cuthbert Micron Technology From: John Woodgate [mailto:[email protected]] Sent: Sunday, March 21, 2004 5:27 AM To: [email protected] Cc: [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; drcuthbert; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected] Subject: Re: What is wrong in my 3 meters FAC measurement [email protected] wrote (in <OF570A07AC.7B1B4A15-ON65256E5 [email protected]>) about 'What is wrong in my 3 meters FAC measurement', on Sun, 21 Mar 2004: > Thank you very much for the attention paid and for putting the >data in a tabular format. FAC measurement is at 3 meters and the OATS >measureent is at 10 meters. Field strength measured in 3 meters distance >in FAC is almost equal to the field strength measured at 10 meters >distance in OATS. So prescan passed but final testing failed. I assumed that you had already corrected the figures for the different measurement distance. If you give insufficient data, you WILL get misleading responses. > Please note that the 3.2 db @ 135.6 MHz difference is NOT within >expectations. It is within MY expectations, given the differences between the two sets of tests. -- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
