A launch cable moves the first connection beyond the OTDR’s initial dead zone. A receive cable lets you evaluate the far-end connection. The required lengths depend on the instrument and test settings; one length does not fit every job.
There is no universal launch length
VIAVI explains that longer pulse widths create longer dead zones, so the launch cable needs to clear the dead zone under the chosen settings. A convenient box size or a familiar cable length is not enough to establish suitability.
Ask the supplier to select launch and receive lengths against the exact OTDR module, link lengths and planned pulse settings. If your work mixes short links with long outside-plant runs, describe both cases. Request the assumptions behind the recommendation.
Match the fiber and connector interfaces
The FOA reference-cable guide calls for OTDR reference fibers that match the plant’s fiber type and size. Confirm the interfaces at the instrument and at each end of the link, including connector type and polish. Do not assume a physically similar connector makes a compatible test setup.
List each end explicitly on the purchase request. Where adapters or additional reference leads are needed, ask for exact part numbers and a connection diagram appropriate to the equipment.
Build a connector worksheet before ordering
Write the connection path in order: OTDR port, launch cable, near end of the link, far end of the link, receive cable. Fill in these details before comparing accessory bundles:
- Instrument: exact OTDR and module, test port, fiber type and required wavelengths.
- Launch cable: connector type and polish at the instrument end, then connector type and polish at the link end. Identify the mating interface for each.
- Link ends: near-end and far-end connector types and polishes, recorded separately. Include any patch panels or adapters in the proposed connection diagram.
- Receive cable: link-facing connector and polish, fiber type, and the connector at its other end. Specify the reverse-direction setup too if the test plan requires it.
- Lengths and records: proposed launch/receive lengths, the module and pulse-setting assumptions, and the required report format.
Mark unknown interfaces as unresolved instead of choosing a default. Include this worksheet when you request a complete test-kit configuration.
Cable selection and compensation are separate checks
Fluke Networks explains that launch/tail compensation removes the reference-cable lengths from the OTDR measurements. Its OptiFiber Pro guidance distinguishes a Launch + Fiber + Tail method for links with different connectors at the near and far ends. It also describes Manual Entry (APC) when low-reflectance connectors prevent the tester from finding the correct launch and tail events.
These are OptiFiber Pro examples. Ask for the applicable compensation procedure for the exact instrument, software and cable arrangement being quoted, including how the crew verifies the selected boundaries. Having the right cables does not establish that compensation has been set correctly.
What belongs in the kit quote?
- Launch and receive cable lengths, with the test assumptions.
- Fiber type and connector details at both ends.
- Cases, adapters and any additional reference leads.
- Compatible connector inspection and cleaning tools.
- Manufacturer instructions for setting launch/receive compensation or event markers.
Check the setup again when the job changes
A cable that works with one module and pulse setting may not resolve the first connector under another setup. Ask how to verify that the launch and receive sections are adequate on the trace. Retain that instruction with the test procedure.
The goal is a complete measurement setup, not a tester plus an arbitrary accessory bundle. For the other main selection decisions, read singlemode, multimode and live-fiber requirements.
Common buying questions
Is a 100-meter launch cable always enough?
No. Required length depends on the instrument’s dead zone at the settings used. Ask for a recommendation tied to your exact module and test plan.
Do launch and receive cables need matching fiber?
Match the reference fiber to the plant’s fiber type and size, and confirm all connector interfaces.
Sources & scope
Prepared September 11, 2026. Updated September 23, 2026 from the references below. Selection guidance is editorial synthesis; no hands-on product testing is claimed. Confirm the current configuration and operating instructions with the manufacturer.