Cisco GS7000 Operating instructions

Troubleshooting

This troubleshooting section lists common problems and their solutions. If a troubleshooting procedure directs

you to replace a module of the 1.2 GHz GS7000 Remote PHY Device (RPD) 2X2 Segmentable Node, see

Removing and Replacing Modules.

•No RF Output at Receiver RF Test Point: Optical Power LED on Receiver Module is off, on page 1

•No RF Output: Fiber Optic Light Level is Good, Receiver Optical Power LED is on, on page 3

•Poor C/N Performance, on page 4

•Poor Distortion Performance, on page 6

•Poor Frequency Response, on page 8

•No RF Output from Reverse Receiver, on page 9

•Reference: 2x2 RPD Module LEDs, on page 10

No RF Output at Receiver RF Test Point: Optical Power LED on

Receiver Module is off

Follow this troubleshooting flowchart. Also see the notes following the chart.

Troubleshooting

These notes apply to the previous troubleshooting flowchart.

DescriptionNote

For low input receiverFor standard receiver

This unit will have no RF output.This unit will have no RF output.1

The receiver will not function below this DC

level which is equal to -10 dBm.

• The optimum light level input is -10 to -2

dBm.

• For every 1 dBm change in optical input

power, the RF output will change by 2 dB.

• Excessively high light input levels (> -2

dBm) will cause distortions and/or damage

the photo diode.

The receiver will not function below this DC

level which is equal to -10 dBm.

• The optimum light level input is -6 to 2

dBm.

• For every 1 dBm change in optical input

power, the RF output will change by 2 dB.

• Excessively high light input levels (> +2

dBm) will cause distortions and/or damage

the photo diode.

Troubleshooting

No RF Output at Receiver RF Test Point: Optical Power LED on Receiver Module is off

No RF Output: Fiber Optic Light Level is Good, Receiver Optical

Power LED is on

Follow this troubleshooting flowchart. Also see the notes following the chart.

These notes apply to the previous troubleshooting flowchart.

Troubleshooting

No RF Output: Fiber Optic Light Level is Good, Receiver Optical Power LED is on

DescriptionNote

For low input receiverFor standard receiver

If the green LED is Off, it is outside optical

input range. Green (On) indicates that light is

present and the optical input value is higher than

-14 dBm.

If the green LED is Off, it is outside optical

input range. Green (On) indicates that light is

present and the optical input value is higher than

-10 dBm.

The recommended RF output level at the output

of the receiver module is 27 dBmV (+7.0 dBmV

as measured at the -20 dB RF test point). This

setup is recommended to achieve the best

possible performance with 8 dB setting.

The recommended RF output level at the output

of the receiver module is 27 dBmV (+7.0 dBmV

as measured at the -20 dB RF test point). This

setup is recommended to achieve the best

possible performance.

• Assumes 2.5% OMI/CH or 20% composite.

• Assumes 1310 nm wavelength / Add one dB for 1550.

• Assumes 0dB attenuator switch setting unless noted, if otherwise subtract attenuator value from reading.

• Assumes -4dB optical input, if otherwise add or subtract 2dB RF for each 1dB optical input.

Note

Poor C/N Performance

Follow this troubleshooting flowchart. Also see the notes following the chart.

Troubleshooting

Poor C/N Performance

These notes apply to the previous troubleshooting flowchart.

DescriptionNote

RF drive level to the laser must be set to the laser manufacturer’s specification.1

It is possible that the distribution module is set up incorrectly. See the pad and equalizer selection

charts in Appendix A for correct pad and equalization. The C/N performance will suffer if the

RF levels are too low into the first gain stage or the interstage.

Troubleshooting

Poor C/N Performance

DescriptionNote

It is important to monitor the DC level at the receiver module because in the process of cleaning

the connectors, the transfer of light through each connector may improve or degrade. The DC

reading should degrade if there is a reflection in the path depending on the severity of the core

mismatch. Scratches on the surface of the fiber of the connector can cause reflections. Scratched

connectors must be replaced.

For low input receiver

For standard receiver4

Attenuate the light to simulate the amount of

light that should be at the node and rerun the

C/N performance. Add components into the

path one at a time until the problem is found.

Change jumpers, couplers, fibers and connectors

one at a time, taking C/N measurements after

each change.

A phenomenon called “shot noise” will occur

if the light level is too high into the receiver.

This is noise generated by the photo diode when

the light is converted back to RF. An optical

input level exceeding -2 dBm at the detector

will also generate distortions.

Attenuate the light to simulate the amount of

light that should be at the node and rerun the

C/N performance. Add components into the

path one at a time until the problem is found.

Change jumpers, couplers, fibers and connectors

one at a time, taking C/N measurements after

each change.

A phenomenon called “shot noise” will occur

if the light level is too high into the receiver.

This is noise generated by the photo diode when

the light is converted back to RF. An optical

input level exceeding +2 dBm at the detector

will also generate distortions.

• Assumes 2.5% OMI/CH or 20% composite.

• Assumes 1310 nm wavelength / Add one dB for 1550.

• Assumes 0dB attenuator switch setting unless noted, if otherwise subtract attenuator value from reading.

• Assumes -4dB optical input, if otherwise add or subtract 2dB RF for each 1dB optical input.

Note

Poor Distortion Performance

Follow this troubleshooting flowchart. Also see the notes following the chart.

Troubleshooting

Poor Distortion Performance

These notes apply to the previous troubleshooting flowchart.

DescriptionNote

Recommended RF input levels are:

• Headend transmitter module: 14 dBmV

Based on 79-channel loading. The input will increase as the channel loading decreases.

Note

Troubleshooting

Poor Distortion Performance

DescriptionNote

For low input receiver

For standard receiver2

The range for optical light input level is -10 to

-2 dBm which converts to 0.1 to 0.6 V DC. The

optimum operating range is -6 dBm to -2 dBm

which converts to 0.25 to 0.6 V DC. Levels

higher than -2 dBm can cause the photo diode

to generate distortions, which add to the

distortion performance of the link, effectively

degrading the distortion performance.

The range for optical light input level is -6 to

+2 dBm which converts to 0.25 to 1.6 V DC.

The optimum operating range is -3 dBm to +2

dBm which converts to 0.5 to 1.6 V DC. Levels

higher than +2 dBm can cause the photo diode

to generate distortions, which add to the

distortion performance of the link, effectively

degrading the distortion performance.

Attenuate the light to simulate the amount of light that should be at the 1.2 GHz GS7000 Node

and rerun the distortion performance. If the distortion performance improves, there is too much

light. An inline optical attenuator or a coupler with a higher loss can reduce the light, or the laser

may have to be replaced with a lower launch power.

Attenuate the RF input level into the amplifier by increasing the pad value at the OIB. If the

distortion perform improves, there is too much RF.

Poor Frequency Response

Follow this troubleshooting flowchart. Also see the notes following the chart.

Troubleshooting

Poor Frequency Response

These notes apply to the previous troubleshooting flowchart.

DescriptionNote

Be sure all unused ports are properly terminated into 75 ohms to prevent mismatches. The

frequency response is cumulative and reflects the response of each active device in the link:

• The frequency response for the transmitter is dependent on the transmitter manufacturer's

specification.

• The frequency response of the node is ±1.0 dB from 52 MHz to 1218 MHz (for optical

receiver and amplifier combined).

It is possible that the RF amplifier is set up incorrectly. Always check to see that padding and

equalization is correct to ensure proper levels at the inputs to each gain stage. See the pad and

equalizer selection charts in Technical Information for correct pad and equalization.

No RF Output from Reverse Receiver

Follow this troubleshooting flowchart.

Troubleshooting

No RF Output from Reverse Receiver

Reference: 2x2 RPD Module LEDs

This section contains LED definition for the 2x2 RPD module. It provides a coarse-grained indication of

device connectivity to field technicians during their installation or repair of the RPD.

NotesState IndicatedLED Pattern or ColorLED

Required - Indicates power goodPower-on - InitializingGreen - 2 Hz Flash

Pattern

System

LEDs

Required - Indicates remote SSHv2 session

possible

IP acquired via DHCP,

synchronizing and acquiring

configuration

Green - 4 Hz Flash

Pattern

No faults detectedSystem status good -

Connections good

Green - Steady

Loose connection, connector faults, water

ingress at connector, wavelength mismatch,

etc.

Connection fault - No physical

connection to CIN or RF

interfaces

Red - 2 Hz Flash

Pattern

Wrong DHCP configuration, unreachable

hosts, failed authentication with CCAP

Core, etc.

Configuration fault - Failed

synchronization or failed to

receive configuration from

Principal CCAP Core

Red - 4 Hz Flash

Pattern

Indicates hardware fault, always indicated

by a steadily illuminated LED.

System fault - Device cannot

initialize

Red - Steady

Vendor-defined LED behavior. May

indicate high error rates in CIN or RF

ports, marginal operating conditions, etc.

Warning - RPD operational but

operation is imperfect

Amber - Various

Indicates connection state

Per [IEEE 802.3x]Flash PatternCIN

LEDs

Indicates possible port failure or a port

which has been configured to be disabled

Ethernet port failure or port

administratively disabled

Unilluminated

At least one pilot and/or alignment tone

active

Power-on - Downstream RF

initializing

2 Hz Flash PatternD-RF

LEDs

Awaiting downstream channel set

configuration

Channel or channels activated4 Hz Flash Pattern

Downstream channels operationalDownstream channel set

configuration obtained

Steadily Illuminated

Fault detected in RF port or RF port muted

by CCAP Core

RF port fault or RF port muteUnilluminated

Troubleshooting

Reference: 2x2 RPD Module LEDs

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