Cisco Prisma II Platform Technical References
Prisma II HDTx RF Input Power -6 dB
Offset Technical Bulletin
Offset Technical Bulletin
Overview
Purpose
The purpose of this document is to inform Prisma II
™
High Density Transmitter
(HDTx) users of a possible issue in which the RF input power indicated on the
LCI or ICIM is 6 dB below the actual power level.
Audience
This document is written for system engineers and managers responsible for
operating or maintaining Prisma II equipment.
Situation
Cisco has received customer comments that some High Density Transmitters
(HDTx) indicate RF input power of -5 to -7 dB when they should indicate 0 dB
under nominal loading.
Analysis conducted by Cisco has shown that this problem is associated with the
Analysis conducted by Cisco has shown that this problem is associated with the
HDTx transmitter calibration database. Specifically, an offset value added to the
RF input power measurement when the transmitter is in Continuous Wave (CW)
OFF mode and the feed is a live video signal is in error by 6 dB.
HDTx transmitters are calibrated using the Matrix Generator by placing the
HDTx transmitters are calibrated using the Matrix Generator by placing the
transmitter in CW ON mode and adjusting the software so that transmitter RF
input power indicates 0 dB on the LCI or ICIM under nominal loading. Normally,
when the transmitter is switched from CW ON to CW OFF mode, an offset value
is added in software to maintain the RF input power reading.
In cases affected by the calibration database problem, transmitters calibrated to
In cases affected by the calibration database problem, transmitters calibrated to
indicate 0 dB RF input power under nominal loading in CW ON mode typically
read 5 to 7 dB low when switched to CW OFF mode. In these cases, the
transmitter itself is operating normally. The low power indication only reflects
the offset value error in the HDTx database.