> For the complete documentation index, see [llms.txt](https://help.security.gallagher.com/knowledge-hub/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.security.gallagher.com/knowledge-hub/products/cc-hardware/perimeter-solutions/gallagher-fibre-transceiver/fault-finding-biasing-and-termination.md).

# Fibre Transceiver communication issues

Diagnose HBUS communication issues caused by incorrect biasing, termination, or dirty fibre connections.

{% hint style="info" %}
Read [Configure HBUS biasing and termination](/knowledge-hub/products/cc-hardware/perimeter-solutions/gallagher-fibre-transceiver/fibre-tranceiver-biasing-and-terminati.md) for the required configuration.
{% endhint %}

Use these diagrams to identify biasing and termination faults. Clean disconnected fibre terminations professionally if communication remains intermittent.

### Check the Controller connection

This diagram shows four Fibre Transceivers linking one Controller and five Fence Controllers.

![Fibre transceiver biasing and termination, fault finding diagram](https://328339335-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F6bM8WhlBE9BYizPWJaPN%2Fuploads%2Fgit-blob-3ab80c87dc6feabf118a931bc6ba20b2a1914a78%2FSECHUB-FIBRE-07-fault-finding-diagram.png?alt=media)

The Controller is always a biasing source. Turn off biasing on its connected Fibre Transceiver. Terminate both devices when they are at opposite ends of the HBUS run.

### Check each HBUS run

Each blue line from a Fibre Transceiver is a separate HBUS run. Each run needs one biasing source and termination at both ends.

* Missing biasing causes unreliable HBUS communication
* Incorrect termination reduces reliability

{% hint style="warning" %}
The lowest HBUS run has a Fibre Transceiver in the middle. Do not terminate this unit.
{% endhint %}

![Fault-finding: biasing and termination states at the device end, biased-not-terminated versus biased-and-terminated](https://328339335-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F6bM8WhlBE9BYizPWJaPN%2Fuploads%2Fgit-blob-89213b7d5bcda2da4721e97ac2eb6142311d2f77%2FSECHUB-FIBRE-08-fault-finding-diagram-2.png?alt=media)

### Check biasing sources

Biasing supplies voltage to the HBUS run. Communicating devices pull this voltage down.

A segment is an HBUS run on one physical electrical path. Fibre sections separate segments. Each segment needs exactly one biasing source.

![N11/N12 termination diagram](https://328339335-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F6bM8WhlBE9BYizPWJaPN%2Fuploads%2Fgit-blob-ed67ee3a0fec8aad32bdcb973a5c78eed4dd819f%2FSECHUB-FIBRE-06-n11-n12-termination-diagram.jpeg?alt=media)

***

🔗 **Related**

* [Configure HBUS biasing and termination](/knowledge-hub/products/cc-hardware/perimeter-solutions/gallagher-fibre-transceiver/fibre-tranceiver-biasing-and-terminati.md) defines the configuration requirements.
* [Fibre Transceiver specifications](/knowledge-hub/products/cc-hardware/perimeter-solutions/gallagher-fibre-transceiver/fibre-tranceiver-switch-settings.md) identifies the biasing and termination switches.
* [Connect Fibre Transceiver power and ground](/knowledge-hub/products/cc-hardware/perimeter-solutions/gallagher-fibre-transceiver/fibre-tranceiver-power-requirements.md) explains required ground connections.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation by asking a question.

Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters:

```
GET https://help.security.gallagher.com/knowledge-hub/products/cc-hardware/perimeter-solutions/gallagher-fibre-transceiver/fault-finding-biasing-and-termination.md?ask=<question>&goal=<user_goal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.