Cisco Cisco 1 GHz GainMaker Amplifier Riferimenti tecnici
78-736252-01 Rev D
2
Overview,
Continued
Observations
Laboratory observations have shown that the GainMaker AGC-induced XMOD is
impossible to perceive or measure on a video monitor fed by a single amplifier.
However, in cascade its effect is cumulative and becomes slightly perceptible on a
video screen beginning after the third AGC amplifier in cascade.
We have discovered other facts relating to this issue:
•
We have discovered other facts relating to this issue:
•
The effect is totally eliminated if the system’s AGC pilot channel remains
unmodulated and the lower adjacent channel is not scrambled.
•
The effect is not present in GainMaker amplifiers without AGC installed.
•
The effect can be halted by removing the AGC input attenuator pad, effectively
switching the amplifier to the back-up THERMAL “Amp + Coax” mode.
The Solution
Cisco has identified the source of the effect and a solution to it, and has redesigned
the AGC detector module accordingly. We will replace AGC detector modules as
required in the field (warehouse or deployed). We recommend replacement of the
AGC detector module in GainMaker System Amplifiers under the following
conditions:
•
•
The system uses more than two amplifiers with AGC in cascade. If you have more
than two amplifiers (system amplifiers and line extenders combined) with AGC in
cascade, Cisco recommends reducing the number of amplifiers with unmodified
AGC to no more than two per cascade.
AND
•
•
The system has video modulated on the AGC pilot channel or the lower adjacent
channel to the pilot channel is scrambled.
Replacing AGC modules in line extenders is not necessary since systems typically do
not run more than two line extenders with AGC in any cascade. By replacing the
AGCs in system amplifiers, any perceptible video distortions will be removed from
the system.
Replacing AGC detector modules in installed system amplifiers will not cause a
Replacing AGC detector modules in installed system amplifiers will not cause a
temporary loss of signal. The amplifier cover must be removed to replace the AGC
detector module but the RF path will not be interrupted during the temporary
removal and replacement of the AGC detector module.
Any AGC detector module replacement required for field units should be
Any AGC detector module replacement required for field units should be
coordinated through Cisco Services. They can be contacted at 1-800-722-2009 (press
2 and then 5).
Any GainMaker amplifiers returned to Cisco for repair or any other reason will be
Any GainMaker amplifiers returned to Cisco for repair or any other reason will be
upgraded to the redesigned AGC detector module.