Masterclock GMR5000 User Manual



MasterclockGMRUserManualv2–2016.12
50
LIGHTNINGARRESTOR
In‐linelightningarrestorsaremountedonalowimpedancegroundbetweentheantennaandthepointwherethe
cableentersthebuilding.Theyrequirenoadditionalpowerorwiringexceptthegroundlead.
CABLEDELAY
GPSpositionaswellaspreciseUTCtimeisdeterminedatthepointtheGPSsignalsarereceivedattheantenna.
SincetheantennaistypicallyattachedtotheGPStimingreceiverviaacable,signalpropagationdelaysthroughthe
cablecausethetimecalculatedbythereceivertobeslightly
behindUTC.InGPSclockswithnanosecondand
microsecondaccuraciesthisisacriticalfactor.Inproductssuchasnetworktimeserverscabledelayisnot
importantbecausetimetransferoverIPnetworksdegradesthetimetothemillisecondlevel.
Cabledelayisafunctionofthecabletype.RG‐
59
cableforexampletypicallydelaysthesignal1.24
ns/ft.For50feetofcable(15m)thedelaywould
be62nanoseconds.Cabledelayisremovedby
advancingtheantennasignalinsidetheGPS
receiver.Inthisexample,advancingthesignal+62
nanosecondsremovesallcablelatency.Solutions
suchas
theGPSDown/upconverteralso
introducesignallatencybutthislatencycanalso
beremovedbyadjustingthesignal.Allprecision
GPStimingreceiverswithnanosecondor
microsecondtimingaccuracyhavetheabilityto
compensateforcabledelay.

ADVANCEDPLANNING
ItistimewellspenttoestimateinadvancethecablelengthfromtheGPSantennatothereceiverforanyplanned
installation.Cablelengthsthataretooshortortoolongcaneachintroduceproblems.Insomecases,addingan
inlineamplifierandsomeextracablemaybeaquick
andeconomicalsolution.Inotherinstances,retrofittingfora
GPSdown/upconvertermaybenecessarywhichwillrequireinstallingadifferentcabletype.Keepinmindthat
someextracablecoiledinaceilingleftoverfromoverestimatingthecablelengthisnotnecessarilynegative.
Providedyouknowthelength
ofthetotalcable,thecabledelaycanbeaccountedforandthetimingaccuracy
maintained.





Masterclock GMR5000 Specifications

General

Brand	Masterclock
Model	GMR5000
Category	Control Unit
Language	English