{"id":2885,"date":"2022-03-09T09:30:57","date_gmt":"2022-03-09T13:30:57","guid":{"rendered":"http:\/\/www.summersidearc.com\/?p=2885"},"modified":"2022-03-09T09:30:57","modified_gmt":"2022-03-09T13:30:57","slug":"emi-and-rfi-some-causes-and-cures","status":"publish","type":"post","link":"http:\/\/www.summersidearc.com\/index.php\/2022\/03\/09\/emi-and-rfi-some-causes-and-cures\/","title":{"rendered":"EMI and RFI \u2013 Some Causes and Cures&#8230;."},"content":{"rendered":"<h2>EMI and RFI \u2013 Some Causes and Cures<\/h2>\n<p>Created by Howard L Walker, KI4VEO on 2022-03-08<\/p>\n<div class=\"borderbox\">\n<p>A broad sweep review of the causes and cures and techniques for reducing RFI\/ EMI<\/p>\n<p>Note: This article was published in the May 1980 issue of R.F. Design magazine<\/p>\n<p>Author:\u00a0 Howard Walker (KI4VEO)<\/p>\n<p>Publisher:\u00a0 Cardiff Publishing Company<\/p>\n<p><strong>EMI Defined<\/strong><\/p>\n<p>Technically, EMI is, \u201cany Electrical or Electromagnetic phenomenon &#8211; Man Made or natural \u2013 causing an undesirable response, performance degradation, or complete malfunction of operational electronic equipment.\u00a0 EMI varies, in time and degree, from a nuisance to complete destruction of mission performance.\u201d<\/p>\n<p>The sources of EMI are seemingly unlimited.\u00a0 In fact, any electromechanical, electric, or electronic device is a possible source of EMI.\u00a0 Even mother nature is sometimes the culprit via atmospheric and cosmic disturbances.<\/p>\n<p><strong>3 Major Causes of EMI:<\/strong><\/p>\n<ul>\n<li><strong>Natural Sources \u2013\u00a0<\/strong>Generally due to lightning<\/li>\n<li><strong>Galactic \u2013<\/strong>\u00a0Originates outside the earth\u2019s atmosphere.\u00a0 Caused by solar flares of our sun or other stars millions of miles away.\u00a0 This noise is usually found between 18 and 500 MHz.<\/li>\n<li><strong>Man-<\/strong>Made \u2013 Due mostly to motors, power lines and transformers, neon signs, vehicle ignition, and medical and industrial equipment.\u00a0 This type mainly occurs below 20 MHz.<\/li>\n<\/ul>\n<p>Man-made EMI sources include equipment whose function is to intentionally generate or radiate electromagnetic signals, and equipment that unintentionally generates electromagnetic energy.\u00a0 Unfortunately, even when electromagnetic energy is intentionally generated and presumed restricted to the fundamental or intended frequency range. It sometimes generates harmonic frequencies that cause interference problems with other equipment.<\/p>\n<p>EMI has been a factor since the first electromagnetic wave was propagated intentionally.\u00a0 Also known as Radio Noise, Electrical Noise, and Radio Frequency Interference (RFI), it covers the spectrum DC to light frequencies.<\/p>\n<p>Until recently, users and manufacturers of electrical and electronic equipment were able to ignore the EMI generated by their equipment.\u00a0 Now, however, more stringent regulations make manufacturers and users alike responsible for interference caused by their equipment.<\/p>\n<p>More stringent regulations have been necessitated, not only by the abundance of equipment crowding the spectrum, but also by the nature of the modern developments.\u00a0 The increased use of semiconductors and integrated circuits, as well as the increased\u00a0 use of plastics in cabinets and housings; instead of metal, have caused a problem with EMI leakage into, as well as, out of equipment.<\/p>\n<p>Plastics have many advantages, but like all insulators, they are poor EMI shields; without special conductivity treatment.\u00a0 Although susceptibility to EMI may be reduced by filtering, this must be augmented with good design of housing and cabinets.\u00a0 The housing should act as a two-way shield, either keeping the EMI out; or in the case of an EMI generating device; keeping it in.<\/p>\n<p>The ultimate goal of the various EMI specifications is to ensure Electromagnetic Compatibility (EMC) \u2013 that equipment and systems will function as designed without degradation of malfunction in their intended operation electronic environment nor adversely affect the operation of any other equipment or system.<\/p>\n<p>The FCC has the responsibility of controlling the generation of any electrical interference that hampers communications.<\/p>\n<p>The FCC is only one of the many government agencies involved in regulating policy and controlling EMI.\u00a0 The other primary agencies are:<\/p>\n<ul>\n<li>Office of Telecommunications Policy (OTP)<\/li>\n<li>Office of Telecommunications<\/li>\n<li>Department of Commerce<\/li>\n<li>Department of Defense (DOD) and it\u2019s Tri-Service Executive Agencies<\/li>\n<li>National Aeronautics and Space Administration (NASA)<\/li>\n<li>Department of Transportation (DOT), including it\u2019s Federal Aviation Agency (FAA)<\/li>\n<li>Bureau of Radiological Health (BRH)<\/li>\n<li>The National Security Agency (NSA)<\/li>\n<\/ul>\n<p>In addition, there are many others such as the National Bureau of Standards and the Environmental Sciences and Service Administration, which play and important role in EMI, but are not responsible for issuing EMI specifications, rules, regulations and policy.<\/p>\n<p>&nbsp;<\/p>\n<p><strong>Eliminating EMI:\u00a0<\/strong><strong>\u00a0<\/strong><\/p>\n<p>Equipment redesign is not cost effective and, often times, not EMI effective.\u00a0 Prevention seems to be the most practical procedure, both in terms of economics and results.\u00a0 Grounding, shielding, balanced lines, twisted pairs, and filtering methods are used to prevent or contain EMI.<\/p>\n<ul>\n<li><strong>Grounding<\/strong><\/li>\n<\/ul>\n<p>A proper ground, for interference reduction, should be a zero impedance point which serves as a single reference point.\u00a0 Since no two points are at the same electrical potential, multiple ground connections introduce a \u201cground loop\u201d, which conducts interference to other parts of the system.<\/p>\n<p>Grounding should not be considered a cure-all, however.\u00a0 In some cases it may be necessary to be used\u00a0<em>with<\/em>\u00a0shielding.\u00a0 But,\u00a0<em>grounding is not shielding<\/em>.\u00a0 The housing sections may be grounded. But still leak (radiation).<\/p>\n<ul>\n<li><strong>Shielding<\/strong><\/li>\n<\/ul>\n<p>Electric (E) and magnetic (H) fields travel through free space at 3 X 10<sup>8<\/sup>\u00a0meters\/second.\u00a0 When these waves strike a conductor, some energy is reflected and the incident wave also sets up eddy currents in the conductor, which attenuate the signal.\u00a0 Thus, a shield reduces the effect of the electromagnetic wave by reflection and energy absorption.<\/p>\n<p>For electrically thick material:<\/p>\n<p>R= 50 + 10 log<sub>10\u00a0<\/sub>(PBf) &#8211; 1<\/p>\n<p>A = 1.7t (f\/PB) .5<\/p>\n<p>Where R = Reflected Wave in db<\/p>\n<p>A = Absorbed Wave in db<\/p>\n<p>PB = in ohms\/cm<\/p>\n<p>f = Frequency in MHz<\/p>\n<p>t = Thickness in cm<\/p>\n<p>A is dependent on frequency, thickness, conductivity and permeability of the shield material.<\/p>\n<p>A major problem with shielding is that any discontinuity in the shield can leak EMI.<\/p>\n<p>Shielding in plastic cabinets can be achieved using:<\/p>\n<p><em>Conductive Foil<\/em>\u00a0\u2013 Generally applied inside the cabinet.\u00a0 It usually requires a coating to prevent corrosion.\u00a0 Effectiveness of 55-100 db for 5 mil thickness is achievable.<\/p>\n<p><em>Conductive Coatings<\/em>\u00a0\u2013 Also applied inside cabinets.\u00a0 Coatings include graphite, silver, nickel and zinc.\u00a0 The first three are applied with an organic solvent carrier.\u00a0 Arc and flame spraying techniques are used to apply zinc by utilizing an electrical current or gas flame to melt zinc or a zinc alloy wire.\u00a0 Droplets of the metal are then blown onto the housing surface through an air jet.<\/p>\n<p><em>Conductive Plastics<\/em>\u00a0\u2013 Thermoset and Thermoplastic resins are made conductive with the addition of metal flakes or fibers, carbon powder or graphite fibers.<\/p>\n<p>&nbsp;<\/p>\n<ul>\n<li><strong>Shielding for RFI:<\/strong><\/li>\n<\/ul>\n<p>Shielding is perhaps the most important method of preventing or curing RFI.\u00a0 Maximum effects of a particular type shield are realized when there are no breaks or points of entry (in the shielding).<\/p>\n<p><em>Ventilation Holes<\/em>\u00a0\u2013 Honeycomb type vent holes are effective in that the small tubing of the honeycomb act as a waveguide below cutoff.<\/p>\n<p><em>Coaxial Cable<\/em>\u00a0\u2013 Proper termination is a must.\u00a0 The braid should be soldered so that the inner conductor is surrounded by the braid at the termination point.<\/p>\n<p>Improperly designed openings in keyboards or ports, and faulty welding can act as waveguide antennas.\u00a0 Above 100 MHz, leakage is serious, as the required slot size becomes smaller.\u00a0 The slots length, not the width, or area, determine its shielding effectiveness.\u00a0 For slot lengths smaller that the interference wavelength an enclosure will shield.\u00a0 However, as the frequency is increased, shielding effectiveness reaches a minimum at the slot resonant frequency.<\/p>\n<p>Panels must be in full contact with the body of the housing.\u00a0 A conductive gasket (i.e. braid or graphite impregnated rubber) must be used.\u00a0 In the case of two or more major housing sections, self-tapping screws are wise to use to attain maximum conductivity.<\/p>\n<p>&nbsp;<\/p>\n<ul>\n<li><strong>Coaxial Cable<\/strong><\/li>\n<\/ul>\n<p>Provides an effective means of shielding an interconnecting line against interference and reducing radiation from the line.<\/p>\n<ul>\n<li><strong>Balanced Lines<\/strong><\/li>\n<\/ul>\n<p>This method to minimize EMI susceptibility utilized a\u00a0<em>balun<\/em>\u00a0transformer at the source and load.\u00a0 Primary and secondary windings are shielded from each other and the transformers are usually grounded.\u00a0 Balanced lines minimize induced voltages and currents caused by interfering fields and interference caused by differences in grounding potential.<\/p>\n<ul>\n<li><strong>Twisted Pairs<\/strong><\/li>\n<\/ul>\n<p>Twisting the conductors along the length of the cable provides signal cancellation of EMI, but the length of the twist is difficult to control.\u00a0 This method is only effective when the EMI frequency wavelength is shorter than the length of the twist.\u00a0 This method is not recommended for use in circuits with multiple grounds.<\/p>\n<ul>\n<li><strong>Filters<\/strong><\/li>\n<\/ul>\n<p>EMI can enter equipment through power and signal lines, or through the enclosure via radiation.\u00a0 The previously mentioned techniques are employed to minimize radiated interference, but they are ineffective against conducted interference.\u00a0 EMI filters on power or signal lines are then called for.<\/p>\n<p>Power line filters, which are usually\u00a0<em>Low<\/em><em>\u00a0Pass<\/em>, are designed to pass frequencies up to the low kHz range.<\/p>\n<p>Filters used on signal and power lines are classified by their type of frequency discrimination.<\/p>\n<ul>\n<li><strong>Low<\/strong><strong>\u00a0Pass<\/strong>\u00a0\u2013 Pass frequencies from DC to a specific cutoff frequency and attenuate all signals above by an increasing amount.<\/li>\n<li><strong>High<\/strong><strong>\u00a0Pass<\/strong>\u00a0\u2013 Pass signals above a specified cutoff frequency and attenuate all signals below by an increasing amount.<\/li>\n<li><strong>Band<\/strong><strong>\u00a0Pass<\/strong>\u00a0\u2013 Pass all signals in a specified band and attenuate all signals above or below cutoff.<\/li>\n<li><strong>Band Reject\u00a0<\/strong>\u2013 Pass all frequencies except those in a specified band.<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<p><strong>Chebyshev and Elliptic Function Filters for RFI:<\/strong><strong>\u00a0<\/strong><\/p>\n<p><strong>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/strong>The Chebyshev low-pass, a common type of filter useful for this application consists of alternating series L and shunt C components.\u00a0 The attenuation<sup>5\u00a0<\/sup>of the filter is specified by<\/p>\n<p>L (dB) = 10 log\u00a0<sub>10\u00a0<\/sub>\u00a0\u00a01 \/ 1 + w e<sup>2\u00a0\u00a0<\/sup>T\u00a0<sub>n<\/sub><sup>2<\/sup>\u00a0(w)<\/p>\n<p>Where<\/p>\n<p>w = 2\u03c0f\u00a0 (f is the frequency in Hertz)<\/p>\n<p>e<sup>2 = \u00a0<\/sup>ripple factor (as a numeric)<\/p>\n<p>T<sub>n<\/sub>\u00a0(w)\u00a0 = Chebyshev polynomial of degrees n<\/p>\n<p>And where<\/p>\n<p>e<sup>2<\/sup>\u00a0= 10\u00a0 ripple (db) \/ 10\u00a0\u00a0 -1<\/p>\n<p>n= total number of L(s) and C(s)<\/p>\n<p>{cos (n arc cos (w)\u00a0\u00a0 0&lt;= w&lt;=1}<\/p>\n<p>T<sub>n<\/sub>\u00a0(w) = \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 {cosh (n arc cosh w)\u00a0\u00a0 w&gt;1\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 }<\/p>\n<p>A more complex and more (characteristic) controllable filter, similar in construction to the Chebyshev, is the elliptic Function filter.\u00a0 The shunt C(s) , of the Chebyshev, are replaced by series L(s) and C (s).\u00a0 This has the advantage of providing a sharper roll-off with increasing frequency (past the 3db or half power point).<\/p>\n<p>Filter selection involves several factors, the first of which are:<\/p>\n<p><strong>Frequency of Operation<\/strong><\/p>\n<p><strong>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/strong>The filter selected must have within its range the frequencies to be filtered.<\/p>\n<p><strong>Working Voltage<\/strong><\/p>\n<p><strong>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/strong>The voltage level of the application must be within the working voltage specification.\u00a0 Most\u00a0<em>commercial<\/em>\u00a0filters are rated in the 125 \u2013 200 VDC range and a few in the 500-600 VDC range.<\/p>\n<p><strong>Insertion Loss<\/strong><\/p>\n<p><strong>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/strong>To accurately determine the amount of insertion loss, impedances within the circuit must be known.\u00a0 Since this is not normally available, a filter is chosen with as high an insertion loss\/volume ratio as possible.<\/p>\n<p><strong>Current Rating<\/strong><\/p>\n<p>The DC current load rating should be 1.5 to 3 times the expected application.<\/p>\n<p><strong>RF Current<\/strong><\/p>\n<p>The type of filter construction limits the amount of RF Power it can dissipate.\u00a0 Some filters incorporate capacitors that will not withstand much RF current, while others convert the RF current to heat.\u00a0 RF current values in most applications are less than .25 amps.<\/p>\n<p><strong>Insulation Resistance<\/strong><\/p>\n<p>This is a function of the dielectric material used in the filter.\u00a0 This parameter determines the leakage current.<\/p>\n<p><strong>Dielectric Voltage Test<\/strong><\/p>\n<p>This is a short term test (5 -60 seconds) that stresses the filter\u2019s dielectric materials 2 \u2013 5 times the working voltage level.<\/p>\n<p><strong>D.C. Resistance<\/strong><\/p>\n<p>This is a function of the length and diameter of the wire used.\u00a0 Basically, it is the resistance of the wire, and it becomes important only in very high current applications where the voltage drop is a concern.<\/p>\n<p><strong>Operating Temperature Range<\/strong><\/p>\n<p>Industry standards are normally -55<sup>o<\/sup>C to 125<sup>o<\/sup>C for military and -25<sup>o<\/sup>C to +85<sup>o<\/sup>C for commercial type applications.\\<\/p>\n<p><strong>Storage Temperature<\/strong><\/p>\n<p><strong>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/strong>Storage temperature is sometimes overlooked.\u00a0 Users often store and transport equipment in environments more severe that the equipment encounters in actual operation.<\/p>\n<p><strong>Noise Generation<\/strong><\/p>\n<p>Thermal noise is caused by agitation of electrons in resistance.\u00a0 The mean square value of thermal noise (E<sup>2<\/sup>) is:<\/p>\n<p>E2 = 4RKT x \u0394f<\/p>\n<p>Where<\/p>\n<p>K = Boltzmann\u2019s Constant (1.38 x 10<sup>-23<\/sup>\u00a0joules \/\u00a0<sup>o<\/sup>K<\/p>\n<p>T = Absolute Temperature (in degrees Kelvin)<\/p>\n<p>\u0394f = Bandwidth (Hz)<\/p>\n<p>R = Resistance (in ohms) or real component of Z<\/p>\n<p><strong>Calculation of Noise Values<\/strong><\/p>\n<p><strong>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/strong>Estimation of noise levels in a receiver, due to external noise, requires taking into account two factors:<\/p>\n<ul>\n<li>Orientation of the receiving antenna<\/li>\n<li>Gain of receiving antenna<\/li>\n<\/ul>\n<p>In general, noise power is proportional to bandwidth.<\/p>\n<p>Thus, where<\/p>\n<p>F<sub>a<\/sub>\u00a0= Effective Antenna Noise Factor<\/p>\n<p>Then<\/p>\n<p>F<sub>a<\/sub>\u00a0= P<sub>n<\/sub>\/KT<sub>o<\/sub>B = T<sub>a<\/sub>\/T<sub>o<\/sub><\/p>\n<p>Where\u00a0 P<sub>n<\/sub>\u00a0= Noise power from equivalent lossless antenna (Watts)<\/p>\n<p>K= Boltzmann\u2019s Constant<\/p>\n<p>T<sub>o<\/sub>\u00a0= Reference Temperature (290<sup>o<\/sup>\u00a0Kelvin)<\/p>\n<p>B = Effective Receiver Noise Bandwidth (Hz)<\/p>\n<p>T<sub>a\u00a0<\/sub>= Effective antenna temperature with external noise (Kelvin)<\/p>\n<p>&nbsp;<\/p>\n<p><strong>References<\/strong><\/p>\n<ol>\n<li>Reference Data for Radio Engineers, Radio Noise and Interference, Atmospheric Noise, Howard W. Sams and Company.<\/li>\n<li>CCIR Report 322\u00a0 10<sup>th<\/sup>\u00a0Plenary Assembly, Geneva; 1963<\/li>\n<li>\u201cEMI Filters\u201d, Hopkins Engineering Co., San Fernando, Calif.<\/li>\n<li>\u201cAMP Quiet Line Filter Handbook\u201d, AMP Incorporated, Harrisburg. Pa.<\/li>\n<li>The Radio Amateur\u2019s Handbook, American Radio Relay League, Newington, Ct.\u00a0 1979<\/li>\n<\/ol>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>EMI and RFI \u2013 Some Causes and Cures Created by Howard L Walker, KI4VEO on 2022-03-08 A broad sweep review of the causes and cures and techniques for reducing RFI\/ EMI Note: This article was published in the May 1980 <a href=\"http:\/\/www.summersidearc.com\/index.php\/2022\/03\/09\/emi-and-rfi-some-causes-and-cures\/\" class=\"read-more\">Read more\u2026 <\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-2885","post","type-post","status-publish","format-standard","hentry","category-archive"],"_links":{"self":[{"href":"http:\/\/www.summersidearc.com\/index.php\/wp-json\/wp\/v2\/posts\/2885","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.summersidearc.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.summersidearc.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.summersidearc.com\/index.php\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"http:\/\/www.summersidearc.com\/index.php\/wp-json\/wp\/v2\/comments?post=2885"}],"version-history":[{"count":1,"href":"http:\/\/www.summersidearc.com\/index.php\/wp-json\/wp\/v2\/posts\/2885\/revisions"}],"predecessor-version":[{"id":2886,"href":"http:\/\/www.summersidearc.com\/index.php\/wp-json\/wp\/v2\/posts\/2885\/revisions\/2886"}],"wp:attachment":[{"href":"http:\/\/www.summersidearc.com\/index.php\/wp-json\/wp\/v2\/media?parent=2885"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.summersidearc.com\/index.php\/wp-json\/wp\/v2\/categories?post=2885"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.summersidearc.com\/index.php\/wp-json\/wp\/v2\/tags?post=2885"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}