Rau ntau tus kws tshaj lij kev sib txuas lus, cov ntsiab lus xws li 'kev nthuav tawm qeeb' thiab 'kev ncua skew' ua rau lub siab mob nco txog cov chav kawm physics hauv tsev kawm theem siab.Hauv kev muaj tiag, qhov cuam tshuam ntawm kev ncua thiab ncua skew ntawm cov teeb liab kis tau yooj yim piav qhia thiab nkag siab.
Kev ncua yog ib qho cuab yeej uas paub tias muaj nyob rau txhua hom kev sib kis xov xwm.Qhov kev nthuav tawm qeeb yog sib npaug rau lub sijhawm uas dhau los ntawm thaum lub teeb liab xa mus thiab thaum nws tau txais nyob rau lwm qhov kawg ntawm cov kab hluav taws xob.Cov nyhuv zoo ib yam li qhov ncua sij hawm nruab nrab ntawm thaum xob laim thiab thunder hnov-tshwj tsis yog tias cov teeb liab hluav taws xob mus nrawm dua li suab.Tus nqi ncua sij hawm rau twisted-pair cabling yog ib qho kev ua haujlwm ntawm nominal velocity of propagation (NVP), ntev thiab zaus.
NVP sib txawv raws li cov khoom siv dielectric siv hauv cable thiab qhia raws li feem pua ntawm qhov ceev ntawm lub teeb.Piv txwv li, feem ntau pawg 5 polyethylene (FRPE) kev tsim kho muaj NVP thaj tsam ntawm 0.65cto0.70c (qhov "c" sawv cev rau qhov ceev ntawm lub teeb ~ 3 x108 m / s) thaum ntsuas ntawm cable tiav.Teflon (FEP) cable siv nyob rau hauv ntau yam ntawm 0.69cto0.73c, whereas cables ua los ntawm PVC yog nyob rau hauv lub 0.60cto0.64crange.
NVP qis dua qhov tseem ceeb yuav ua rau muaj kev ncua ntxiv rau qhov ntev ntawm cable, ib yam li qhov nce ntawm qhov kawg-rau-kawg cable ntev yuav ua rau qhov sib npaug ntawm qhov kawg-rau-kawg qeeb.Raws li nrog rau feem ntau lwm yam kis tsis tau, ncua qhov tseem ceeb yog zaus nyob ntawm.
Thaum ntau tus khub hauv tib lub cable nthuav tawm qhov sib txawv ncua kev ua haujlwm, qhov tshwm sim yog ncua skew.Kev ncua skew yog txiav txim siab los ntawm kev ntsuas qhov sib txawv ntawm cov khub nrog qhov ncua sij hawm tsawg tshaj plaws thiab cov khub nrog qhov qeeb tshaj plaws.Cov yam tseem ceeb uas cuam tshuam qhov kev ncua sij hawm muaj xws li kev xaiv cov khoom siv, xws li cov khoom siv hluav taws xob, thiab kev tsim lub cev, xws li qhov sib txawv ntawm qhov sib tw ntawm tus khub mus rau ib khub.
Kev nthuav qhia Cable ncua
Txawm hais tias txhua qhov sib tw-pair cables nthuav tawm qeeb skew rau qee qhov kev kawm, cov cables uas tau tsim los ua kom muaj kev sib txawv hauv NVP thiab khub-rau-pair ntev qhov sib txawv yuav muaj peev xwm ncua skew rau cov qauv-raws li kab rov tav channel configurations.Qee yam ntawm cov yam ntxwv uas tuaj yeem cuam tshuam kev ncua sij hawm skew kev ua tau zoo suav nrog cov kab hluav taws xob uas tsis zoo tsim los ntawm cov khoom siv hluav taws xob thiab cov uas muaj qhov sib txawv ntawm qhov sib tw-rau-pair twist.
Kev nthuav tawm qeeb thiab qeeb skew kev ua tau zoo tau teev tseg los ntawm qee qhov chaw hauv cheeb tsam network (LAN) cov qauv rau qhov phem tshaj 100 mchannel configurations los xyuas kom meej cov teeb liab kis tau tus mob.Cov teeb meem kis tau tus mob cuam tshuam nrog kev ncua ntau dhau thiab ncua skew suav nrog nce jitter thiab me ntsis yuam kev.Raws li IEEE 802-series LAN specifications, qhov siab tshaj plaws propagation ncua ntawm 570 ns / 100mat 1 MHz thiab qhov siab tshaj plaws ncua sij hawm ntawm 45ns / 100mup txog 100 MHz yog nyob rau hauv kev txiav txim siab los ntawm TIA rau qeb 3, 4 thiab 5, 4-pair cables.TIA Ua Haujlwm Pab Pawg TR41.8.1 tseem tab tom xav txog kev txhim kho cov kev xav tau los ntsuas kev nthuav tawm qeeb thiab qeeb skew rau 100 ohm kab rov tav txuas thiab cov channel uas tau tsim ua raws li ANSI/TIA/EIA-568-A.Raws li qhov tshwm sim ntawm TIA pawg neeg "Letter Ballot" TR-41:94-4 (PN-3772) nws tau txiav txim siab thaum lub Cuaj Hlis 1996 lub rooj sib tham los tshaj tawm "Kev Lag Luam Kev Lag Luam" ntawm tsab ntawv kho dua ua ntej tso tawm.Tseem tsis tau daws teeb meem yog qhov teeb meem ntawm seb cov npe ntawm pawg yuav hloov li cas (piv txwv li, qeb 5.1), kom muaj kev cuam tshuam qhov sib txawv ntawm cov cables uas tau sim rau kev ncua sij hawm ntxiv / ncua skew, thiab cov uas tsis yog.
Txawm hais tias kev nthuav tawm qeeb thiab qeeb skew tau txais kev saib xyuas ntau, nws yog ib qho tseem ceeb uas yuav tsum nco ntsoov tias qhov teeb meem tseem ceeb tshaj plaws ntawm kev ua haujlwm cabling rau feem ntau LAN daim ntawv thov tseem yuav tsum tau txo qis rau crosstalk piv (ACR).Whereas ACR margins txhim kho cov teeb liab rau cov suab nrov sib piv thiab yog li txo qhov tshwm sim ntawm qhov yuam kev me ntsis, qhov kev ua haujlwm ntawm lub cev tsis zoo li cuam tshuam ncaj qha los ntawm cov kab txuas nrog qhov tseem ceeb qeeb skew margins.Piv txwv li, 15 ns ncua skew rau cov kab txuas txuas feem ntau yuav tsis ua rau muaj kev ua tau zoo hauv kev sib txuas ntau dua li 45 ns, rau lub kaw lus tsim los ua kom ntev txog 50 ns ntawm kev ncua skew.
Vim li no, kev siv cov cables nrog kev ncua qeeb skew margins muaj txiaj ntsig ntau dua rau kev pov hwm lawv muab tawm tsam kev teeb tsa lossis lwm yam uas yuav txwv tsis pub thawb ncua skew tshaj qhov txwv, ntau dua li cov lus cog tseg ntawm kev ua haujlwm zoo dua piv rau cov channel uas. tsuas yog ua tau raws li qhov system ncua skew txwv los ntawm ob peb nanoseconds.
Vim tias cov cables uas siv cov khoom sib txawv dielectric rau cov khub sib txawv tau pom muaj teeb meem nrog kev ncua sij hawm, muaj kev tsis sib haum xeeb tsis ntev los no txog kev siv cov khoom sib xyaw dielectric hauv kev tsim kho cable.Cov ntsiab lus xws li "2 los ntawm 2" (ib lub cable muaj ob khub nrog cov khoom siv hluav taws xob "A" thiab ob khub nrog cov khoom "B") lossis "4 los ntawm 0" (ib lub cable muaj plaub khub ua los ntawm cov khoom A, lossis cov khoom B ) uas yog cov lus qhia ntau dua ntawm cov ntoo dua li cable, qee zaum siv los piav txog kev tsim kho dielectric.
Txawm hais tias kev lag luam hype uas tuaj yeem ua rau ib tus neeg ntseeg tias tsuas yog kev tsim kho uas muaj ib hom khoom siv dielectric yuav pom tau qhov kev ua tau zoo qeeb, qhov tseeb yog tias cov cables tsim tau zoo muaj ib qho khoom siv dielectric, lossis ntau yam khoom siv dielectric sib npaug muaj peev xwm txaus siab txawm tias Feem ntau cov channel qeeb qeeb skew yuav tsum tau teev tseg los ntawm daim ntawv thov cov qauv thiab cov uas tau txiav txim siab los ntawm TIA.
Hauv qee qhov xwm txheej, kev tsim vaj tsev sib xyaw dielectric tej zaum yuav raug siv los cuam tshuam qhov sib txawv ntawm qhov sib txawv uas tshwm sim los ntawm qhov sib txawv sib txawv.Daim duab 1 thiab 2 qhia txog tus neeg sawv cev ncua sij hawm thiab skew qhov tseem ceeb tau los ntawm kev xaiv 100 meter cable qauv uas muaj "2 los ntawm 2" (FRPE / FEP) kev tsim kho.Nco ntsoov tias qhov siab tshaj plaws kev nthuav tawm qeeb thiab qeeb skew rau cov qauv no yog 511 ns / 100mand 34 ns, feem ntau ntawm 1 MHz txog 100 MHz.
Post lub sij hawm: Mar-23-2023