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42

 

Common Diagnostic Techniques

 

www.ets-lindgren.com 

 

C

OMMON 

M

ODE 

T

ECHNIQUES

 

 

Some traditional common mode techniques 

do not work in differential mode situations 

 

Once a common mode problem is determined, use techniques which have a 
good potential for success. Start by analyzing the ground and power distribution 
system. Understand what RF impedances these systems present, and then 
reduce the excessive impedance. These techniques can be tried: 

Summary of Contents for ETS-Lindgren 7405

Page 1: ...Model 7405 Near Field Probe Set User Manual...

Page 2: ...ii www ets lindgren com...

Page 3: ...ight 1996 2022 by ETS Lindgren Inc All Rights Reserved No part of this document may be copied by any means without written permission from ETS Lindgren Inc Trademarks used in this document The ETS Lin...

Page 4: ...ormation Bulletin 10 2 0 Maintenance 11 Service Procedures 11 3 0 Specifications 13 Model 7405 13 Preamplifier 13 4 0 Operation 15 Typical Configuration 15 Probe Selection 16 Preamplifier Use 17 5 0 T...

Page 5: ...niffer Probes 32 Diagnosing Radiation Causes 33 Common and Differential Mode Current Flow 35 Differential Mode Techniques 40 Common Mode Techniques 42 Pre Screening Alternate Solutions 43 Evaluating A...

Page 6: ...amage Included text gives proper procedures Warning Denotes a hazard Failure to follow instructions could result in SEVERE personal injury and or property damage Included text gives proper procedures...

Page 7: ...ht weight and compact The probes provide a fast and easy means of detecting and identifying signal sources that could prevent a product from meeting federal regulatory requirements This set is a conve...

Page 8: ...ch creates a balanced E field shield of the coax shield The loops reject E field signals due to the balanced shield Electric E Field Probes The Model 7405 includes two E field probes the stub probe mo...

Page 9: ...ich serves as an E field pick up The absence of a closed loop prevents current flow allowing the ball probe to reject the H field STUB PROBE The model 905 stub probe is made of a single piece of 50 oh...

Page 10: ...Lindgren Product Information Bulletin See the ETS Lindgren Product Information Bulletin included with your shipment for the following Warranty information Safety regulatory and other product marking...

Page 11: ...with your shipment Maintenance of the Model 7405 is limited to external components such as cables or connectors If you have any questions concerning maintenance contact ETS Lindgren Customer Service...

Page 12: ...12 Maintenance www ets lindgren com This page intentionally left blank...

Page 13: ...5 GHz 903 1 cm loop H Field 11 dB 2 3 GHz 904 3 6 cm ball E Field 30 dB 1 GHz 905 6 mm stub tip E Field 30 dB 3 GHz Preamplifier Absolute Maximum Ratings Input Voltage DC 12 VDC Input Voltage AC 20 d...

Page 14: ...14 Specifications www ets lindgren com Environmental Storage and Operating Temperature 0 C to 45 C 32 F to 113 F...

Page 15: ...shipment Typical Configuration 1 Choose the appropriate probe from the Model 7405 Near Field Probe Set See Probe Selection on page 16 2 Connect a coaxial cable from the probe to the signal analyzing d...

Page 16: ...are the most sensitive of the E field and H field probes The stub probe and the 1 cm loop are the least sensitive The frequency of the signal If the signal is above 790 MHz the probe may go into reso...

Page 17: ...ing This kind of refinement provides the ability to stop the radiation at the source rather than shielding an entire unit Preamplifier Use The optional preamplifier increases the sensitivity of your t...

Page 18: ...18 Operation www ets lindgren com This page intentionally left blank...

Page 19: ...e probe the field amplitude may be obtained All probes in the Model 7405 Near Field Probe Set were characterized in a transverse electromagnetic mode TEM cell which presented a 377 ohm field The H fie...

Page 20: ...20 Typical Performance Factors www ets lindgren com Magnetic H Field Probes 901 6 CM LOOP...

Page 21: ...www ets lindgren com Typical Performance Factors 21 902 3 CM LOOP...

Page 22: ...22 Typical Performance Factors www ets lindgren com 903 1 CM LOOP...

Page 23: ...www ets lindgren com Typical Performance Factors 23 Electric E Field Probes 904 BALL PROBE...

Page 24: ...24 Typical Performance Factors www ets lindgren com 905 STUB PROBE...

Page 25: ...www ets lindgren com Typical Performance Factors 25 Preamplifier Gain 0 01 MHZ 3 GHZ...

Page 26: ...26 Typical Performance Factors www ets lindgren com This page intentionally left blank...

Page 27: ...ielded room Final qualification must be performed in the required test environment of a screen room or an open field site However a great deal of preliminary EMI testing can be done with a sniffer pro...

Page 28: ...MHz The challenge is to find the EUT function that created the emissions You may be able to connect the probe to a spectrum analyzer and locate the source locating the source of an emanating signal be...

Page 29: ...tune to the signal of interest This essentially changes the spectrum analyzer into a tuned receiver and makes the display a frequency filtered oscilloscope 2 Take the video output off the spectrum ana...

Page 30: ...produce the observed event and also allows greater facility in recognizing the original signal from the altered and often distorted modulated representation Frequently the demodulated picture will co...

Page 31: ...rather roll off the offending components What you have done is mentally transform a frequency domain failure to a time domain picture that you can work on After identifying what the signal of interes...

Page 32: ...signal source Finding both the point of escape from the unit and the actual source provides choice in engineering the solution you may decide to improve the shielding or to suppress the source The mo...

Page 33: ...This section addresses using sniffer probes for a rough estimate of field impedance which is used to diagnose the radiation physics of a given situation Knowing the field impedance can help find solu...

Page 34: ...mode Electric fields require high impedance sources Because the changing potential is isolated by substantial impedance on all lines into the circuit all lines will carry just the forward current The...

Page 35: ...incipally as current related or voltage related Current related problems are normally associated with differential mode situations Likewise voltage problems are normally associated with common mode ci...

Page 36: ...hrough an H field probe Low impedance sources also will give a higher reading in the near field on an H field probe than on an E field probe Alternately high impedance sources will display a rapid fal...

Page 37: ...ation would record two points at 0 5 meters and 1 5 meters from the source along two radials from the source The signal is measured at each point with a probe which is highly selective of the H field...

Page 38: ...behaved Often the best indicator is the relative amplitude The E field probe will have a much higher reading than the H field probe The drop off rate will be faster when measured with the E field pro...

Page 39: ...is predominately electrical or E field In this case the field impedance is relatively high A high field impedance means there is a potential build up across some impedance and this high potential regi...

Page 40: ...common mode situations When differential mode solutions are applied to a common mode problem many of the techniques will prove ineffective For example Reducing circuit loop area The radiating signal...

Page 41: ...umber of gates Therefore suppression of any one of these gates in isolation will not yield much signal reduction Shielding the entire loop A problem arises when deciding where to ground the shield The...

Page 42: ...not work in differential mode situations Once a common mode problem is determined use techniques which have a good potential for success Start by analyzing the ground and power distribution system Und...

Page 43: ...eduction technique has been correctly applied and indicates when you have properly analyzed the problem to the point of designing an effective solution Testing alternate solutions can save time when t...

Page 44: ...f the distance from the source 1 R However the reactive component will fall off proportionate with the reciprocal of multiple powers of the distance from the source 1 RN Typically the reactive field w...

Page 45: ...iate the received field altering the field being measured However technical imprecision does not necessarily eliminate a method Sometimes an attenuation of the field strength in the near field will tr...

Page 46: ...e what the far field results will be most of the points should be one to four meters away Also choose one or two points close to the source If a solution results in a dramatic reduction this point may...

Page 47: ...afety margin For example suppose a signal fails the required limit by 3 dB Once that signal is found in the lab it can be measured in the near field The goal is then to reduce in this near field the 3...

Page 48: ...s involved such as a second source radiating at the same frequency Example A solution that worked in the lab and on the range before 10 00 AM failed later in the day Analysis revealed that the rise in...

Page 49: ...www ets lindgren com EC Declaration of Conformity 49 Appendix A EC Declaration of Conformity...

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