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How to Fight RF Interference with Your Gadgets

When gadgets talk to each other unintentionally, the results can be a

wireless mess.

By Glenn Derene

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March 10, 2011 6:30 AM Text Size: AA AAfter an eternity of chatter and commercials, the ra!io D" is a#o$t to %lay the son& yo$'(e #een )aitin& *or

Then, a*ter a moment o* %re&nant silence, yo$ hear it +o, not yo$r *a(orite t$ne, #$t yo$r least *a(orite so$n!:

a #zzt#a#a#zzt#a#a#zzzzzzzt that %ierces thro$&h yo$r carstereo s%ea-ers The .arrin& interr$%tion is as*amiliar as it is mysterio$s

/ithin moments a cell%hone )ill rin&, either in the ra!io st$!io !ozens o* miles a)ay, or insi!e yo$r o)n(ehicle That's #eca$se )hat yo$'(e .$st hear! is the noisy %$lse o* a cell%hone's transmitter, am%li*ie! #y either

the station's st$!io e$i%ment or yo$r car's stereo /hat yo$ ex%erience!, in other )or!s, is ra!io*re$ency

inter*erence, or

ta-es many *orms, an! they're all $&ly: A h$mmin& micro)a(e cho-es a /ii connection4 a #a#y monitor

#rims )ith noise4 an a$!io recor!in& ma!e )ith a la%to% *izzles an! %o%s has #een an irritant thro$&ho$t

man-in!'s lo(e a**air )ith electronics, %artic$larly )ith )ireless &a!&ets So )hat is it5 o) can yo$ sto% it5

Radio !eracti!e

7lectroma&netic ra!iation lies #ehin! e(erythin& *rom &amma rays to (isi#le li&ht to yo$r -i!'s )al-ietal-ie

/e $se only a %ortion o* the s%ectr$m *or )ireless comm$nication, the #roa! s)ath *rom a#o$t 30 z to 300Gz 8i&hschool %hysics re*resher: /a(elen&ths &et shorter as *re$ency &ets hi&her, an! a 1Gz )a(e

meas$res a#o$t 12 inches9 an&e, antenna size an! cost re$irements cons%ire )ith strin&ent &o(ernment

re&$lations to rele&ate most %ersonal electronics to an e(en narro)er ran&e o* *re$encies This, a thin, %atchy section o* the electroma&netic s%ectr$m #elo) Gz, is )here o$r &a!&ets li(e Cell%hones, !e%en!in& on the

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carrier, comm$nicate at ;0 Mz, 1< Gz an! 1= Gz /ireless home %hones #roa!cast at =00 Mz, 1=

Gz, 2> Gz an! Gz M ra!io s%ans *rom ; Gz An! )ith so many &a!&ets han&in& aro$n! in s$ch a narro) ran&e o* *re$encies,

thin&s can &et cro)!e! Si&nals can &et crosse!, literally

?Cons$mer electronic !e(ices are !esi&ne! to #e $se! in a certain en(ironment an! interact )ith

electroma&netic *iel!s,? says Carne&ie Mellon electrical an! com%$ter en&ineerin& %ro*essor "ames o#$r&

?An! then yo$ come alon& )ith a so$rce that's creatin& electroma&netic *iel!s that )eren't inten!e! to #e in its

en(ironment? @i-e a noisy en&ine in the #ac-&ro$n! o* an a$!io recor!in&, ra!io*re$ency inter*erence is theres$lt o* a !e(ice ?listenin&? *or one si&nal at a s%eci*ic *re$ency an! ?hearin&? another The 2>Gz

micro)a(e o(er%o)ers the 2>Gz ro$ter an! the la%to% &ets con*$se!

or !eca!es, the CC has trie! to %re(ent this t iss$es re&$lations that co(er #oth a !e(ice's ?noise?

$ninten!e!, $seless emissions, li-e those *rom a sho!!ily shiel!e! micro)a(ean! its s$sce%ti#ility to

inter*erence *rom other &a!&ets ?The %eo%le in the re&$latory #$siness %ro!$ce stan!ar!s *or emissions an!stan!ar!s *or imm$nity, or s$sce%ti#ility, that sho$l! match, so that nothin& emits more than anythin& else can

tolerate,? says Brian @a)rence, exec$ti(e !irector o* the nternational Association *or a!io,

Telecomm$nications an! 7lectroma&netics 8i+AT79 ?/e -no), ho)e(er, that thin&s &o )ron&? r tore%hrase, thin&s &o #zzt#a#a#zzt#a#a#zzzzzzzt

What"s #y Gadget"s Wa!elength$

a!io*re$ency inter*erence occ$rs )hen the si&nal emitte! #y one !e(ice &ets $nintentionally %ic-e! $% #yanothercreatin& a$!i#le noise or a com%romise! connection Some inter*erence is !$e to #a!ly shiel!e! )ires

or com%onents, #$t some is .$st the res$lt o* too many &a!&ets cro)!e! into a limite! s%ectr$m

%nintended Recei!er

The ex%losion o* com%lexity in electronic !e(ices certainly hasn't ma!e thin&s easier ?* some#o!y, %erha%s

e(en someone )ho's *airly )ell(erse! in the *$nction o* the !e(ice, o%ens a la%to% com%$ter to *ix an

%ro#lem an! !oesn't %$t it #ac- to&ether %ro%erly, or *or&ets a &as-et or e(en one scre) o$t o* se(en, it co$l!!e&ra!e shiel!in&,? says Shirish Shah, %resi!ent o* Com%liant 7lectronics, an 7M 8electroma&netic

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inter*erence9 testin& *irm A la%to% contains !ozens o* small emitters, the ra!iation an! s$sce%ti#ility o* )hich

m$st #e acco$nte! *or

Des%ite this com%lexity, Shah says, com%anies are res%on!in& )ith #etter !e(ices an! #etter com%liance The

only exce%tion5 ?/hen o**shore com%anies try to re!$ce costs or c$t corners? @a)rence echoes the sentiment?/e ha(e a#!icate! man$*act$rin& res%onsi#ility to !e(elo%in& nations, )here the ex%ertise is not as )ell

esta#lishe! as it sho$l! #e?

B$t a mere ex%lanation is col! com*ort to the #$zza**licte!, an! a tho$san! reasons aren't )orth a sin&lesol$tion n*ort$nately, li*e is to$&h *or a D )arrior The con(entional )is!om a#o$t ins$latin& *rom

heat or so$n! !oesn't really a%%ly to shiel!s 8or exam%le, a thinner shiel! may #e more e**ecti(e than a

thic-er one, since its a#ility to atten$ate is !etermine! in %art #y the )a(elen&th o* the ra!iation9 $rthermore,a %oorly !esi&ne! shiel! co$l! act$ally ret$ne emissions to another *re$ency, re%lacin& one ty%e o*

inter*erence )ith another 8n the case o* !e!icate! *ilters *or %o)er an! %hone connectors, as )ell as *or

ra!io an! tele(ision antenna lea!s, each $nit atten$ates certain *re$encies #$t not others9

&and #anagement

The enth$siast's #est )ea%on a&ainst is the a#ility to a!a%t * an ol!er cor!less %hone is %la&$e! )ithinter*erence, it's )orth loo-in& into a ne) han!set Mo!ern )ireless %hones ha(e mo(e! *rom o(ercro)!e!*re$encies, s$ch as 2> Gz, share! )ith /ii ro$ters an! micro)a(e o(ens, to more %eace*$l %ast$res, most

commonly #y )ay o* the Di&ital 7nhance! Cor!less Telecomm$nications 8D7CT9 60 stan!ar! D7CT o%erates

at aro$n! 1= Gz, a *re$ency ran&e *ar a)ay *rom most common, noncomm$nications ca$ses o* inter*erence,an! $ses cle(erly controlle!, min$te *re$ency chan&es to a(oi! )hat little !ist$r#ance may cro% $% *rom

cell%hones an! other D7CT !e(ices @i-e)ise, ne)er /ireless + ro$ters are a#le to o%erate in another

relati(ely $iet #an! o* *re$encies, near Gz

That's not to say that #$yin& ne) &ear is the only o%tion As mentione! earlier, a$!io e$i%ment can am%li*y

noise *rom certain cell%hones 8iEhones are -no)n *or this, altho$&h other %hones can ca$se %ro#lems as )ell9

* yo$r %hone is #$zzin& thro$&h yo$r s%ea-ers, yo$ may #e a#le to s)itch the *re$encies the %hone o%erateson, *rom ;0 Mz 8o*ten la#ele! as 7DG79 to hi&her, 3G *re$encies Chan&in& this settin&, )hich can #e

*o$n! in most %hones' con*i&$ration men$s, can ne&ati(ely a**ect !ata s%ee!s an! si&nal stren&th, #$t it'll

almost al)ays -ill that annoyin& #$zz Also, chea% *errite #ea!s can *ilter o$t These #ea!s can #e #o$&ht*rom electronics stores or c$t *rom the )ei&hte! cylin!ers *o$n! on many chea% SB ca#les an! then )ra%%e!

aro$n! the )ires r$nnin& *rom an a$!io so$rce to the am%li*ier or, in rare cases, aro$n! the s%ea-er )ires

themsel(es

Elacement also co$nts *or a lot 7lectroma&netic *iel!s !ro% o** $ic-ly, so -ee%in& a cell%hone .$st > or *eet

*rom ($lnera#le s%ea-ers or am%li*iers )ill $s$ally !$ll inter*erence so$n!s #eyon! %erce%tion A /ii

attac-in& micro)a(e can #e th)arte! #y -ee%in& ro$ters an! )ireless !e(ices at least 10 to 1 *eet a)ay * a

CT monitor or stereo am%li*ier &i(es yo$ %ersistent tro$#le, chec- *or less o#(io$s, near#y emitters Anythin&)ith an electric motor, s$ch as an AC $nit, can %ro!$ce some nasty noise, #$t rarely !o these *iel!s reach (ery

*ar /hen it comes to , a little !istance can &o a lon& )ay