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What Is an OTDR Launch Cable Box? Uses, Selection Guide & FAQ

by Fusion Splicer

When testing fiber optic networks with an OTDR (Optical Time Domain Reflectometer), one of the most common challenges engineers face is the dead zone — a blind spot at the very beginning of the fiber trace where the instrument cannot accurately measure events. The solution is a launch cable box, also called a dead zone eliminator or OTDR launch fiber reel.

This guide explains what a launch cable box is, when and why you need one, how to select the right product for your application, and answers the most frequently asked questions from fiber optic technicians worldwide.

What Is an OTDR Launch Cable Box?

An OTDR launch cable box is a pre-wound reel of single-mode or multimode optical fiber — typically 100 m to 2,000 m in length — that is connected between the OTDR port and the fiber under test (FUT). By inserting this known length of fiber before the measurement begins, the OTDR's initial dead zone is pushed past the first connector or splice of the network being tested, allowing accurate characterization of the entire link.

Key terms:

  • Dead zone — The distance after a reflective event (e.g., a connector) during which the OTDR cannot detect another event. Typically 1–10 m for event dead zones and 5–25 m for attenuation dead zones, depending on the instrument.
  • Launch cable / launch fiber — The fiber reel inserted before the FUT to overcome the dead zone.
  • Receive cable — An optional second reel placed at the far end of the FUT to characterize the final connector.

Why Do You Need a Launch Cable Box?

Without a launch cable, the OTDR's initial pulse saturates the detector, creating a dead zone that masks the first connector, splice, or bend in the network. This means:

  • The first connector loss cannot be measured accurately.
  • Reflections at the near end are hidden inside the dead zone.
  • Compliance testing (e.g., TIA-568, IEC 61280-4) requires characterization of all connectors, including the first one.

A launch cable box solves all of these problems by shifting the dead zone to a section of fiber you already know is good.

Common Use Cases

Application Recommended Launch Length
Premises / LAN cabling (short links) 100–500 m
Outside plant (OSP) / metro fiber 500–1,000 m
Long-haul / submarine cable testing 1,000–2,000 m
FTTx / PON network commissioning 500–1,000 m
Data center interconnect (DCI) 100–500 m
Aerial and underground cable acceptance 500–2,000 m

Rule of thumb: Choose a launch cable length that is at least 1.5× the OTDR's event dead zone at the pulse width you plan to use. For most field OTDRs, 500 m is sufficient for short-range testing; 1,000 m or 2,000 m is recommended for long-haul or high-dynamic-range measurements.

How to Use an OTDR Launch Cable Box

  1. Connect the launch cable box output connector to the OTDR's optical port.
  2. Connect the other end of the launch cable to the near-end connector of the fiber under test.
  3. Set the OTDR range and pulse width appropriate for the link length.
  4. Acquire the trace. The launch cable appears as a flat, known-loss section at the beginning of the trace.
  5. Set the start marker at the far end of the launch cable (the first connector of the FUT) to begin measurement.
  6. (Optional) Connect a receive cable at the far end to characterize the final connector.

How to Choose the Right OTDR Launch Cable Box

1. Fiber Type

  • G.652D (OS2) single-mode — The industry standard for telecom and OSP applications. All launch cables in our store use G.652D fiber for maximum compatibility.
  • OM3/OM4 multimode — Required for multimode OTDRs (850/1300 nm). Ensure the fiber type matches your OTDR wavelength.

2. Launch Cable Length

  • 500 m — Ideal for short-range premises and data center testing. Compact and lightweight.
  • 1,000 m — The most versatile choice for field technicians. Covers the dead zone of virtually all field OTDRs at standard pulse widths.
  • 2,000 m — Best for long-haul, high-dynamic-range, or submarine cable testing where longer pulse widths create larger dead zones.

3. Connector Type

Choose connectors that match both your OTDR port and the fiber under test:

  • SC/UPC — Most common for telecom and OSP.
  • SC/APC — Required for PON/FTTx networks (green connector, 8° angled ferrule).
  • FC/UPC or FC/APC — Common on older OTDRs and test equipment.
  • LC/UPC or LC/APC — Used in high-density data center environments.
  • ST/UPC — Legacy enterprise and campus networks.

Tip: Our launch cable boxes are available with mixed connector configurations (e.g., SC/UPC to FC/UPC), so you can match any OTDR port to any network connector without an adapter.

4. Reel Quality and Housing

  • Look for a rugged ABS or aluminum housing that protects the fiber during field use.
  • A smooth, low-friction reel prevents microbends that add insertion loss.
  • IL (Insertion Loss) ≤ 0.3 dB and RL (Return Loss) ≥ 50 dB (UPC) or ≥ 60 dB (APC) per connector end.

Our OTDR Launch Cable Box Products

We stock a full range of G.652D single-mode OTDR launch cable boxes with SC, FC, LC, and ST connectors in UPC and APC polish:

Frequently Asked Questions (FAQ)

What is the difference between a launch cable and a receive cable?

A launch cable is placed at the near end (between the OTDR and the FUT) to eliminate the initial dead zone. A receive cable is placed at the far end to allow the OTDR to fully characterize the last connector of the link. For bidirectional testing or full end-to-end connector characterization, both are recommended.

Can I use any fiber patch cord as a launch cable?

Technically yes, but a dedicated launch cable box is strongly preferred. Patch cords are typically 1–3 m long — far too short to push the dead zone past the first connector. A proper launch cable reel (≥ 100 m) is required for accurate measurements.

Does the launch cable length affect OTDR measurement accuracy?

The launch cable itself introduces a small amount of attenuation (approximately 0.2 dB/km for G.652D fiber), which the OTDR will display as a sloped line at the beginning of the trace. This is expected and does not affect the accuracy of measurements on the FUT. Simply set your start marker at the end of the launch cable.

What connector polish should I choose — UPC or APC?

Match the connector polish to your network. UPC (blue) is standard for most telecom and enterprise networks. APC (green, 8° angle) is required for PON/FTTx and CATV networks where high return loss is critical. Mixing UPC and APC connectors will result in high insertion loss and potential damage to APC ferrules.

How do I know if my OTDR dead zone requires a 500 m, 1,000 m, or 2,000 m launch cable?

Check your OTDR's datasheet for the event dead zone and attenuation dead zone at the pulse width you plan to use. As a general rule:

  • Event dead zone < 5 m → 100–300 m launch cable is sufficient.
  • Event dead zone 5–20 m → 500 m launch cable recommended.
  • Event dead zone > 20 m (long pulse, high dynamic range) → 1,000–2,000 m launch cable required.

Are your launch cable boxes compatible with all OTDR brands?

Yes. Our launch cable boxes use standard SC, FC, LC, and ST connectors and are compatible with all major OTDR brands including EXFO, JDSU/Viavi, Yokogawa, AFL, Fluke Networks, Anritsu, and Fujikura.

What is the insertion loss of your launch cable boxes?

Each connector end is factory-tested to ≤ 0.3 dB insertion loss and ≥ 50 dB return loss (UPC) or ≥ 60 dB return loss (APC). A test report is available upon request.

Can I use a launch cable box with a multimode OTDR?

Our current stock is G.652D single-mode fiber, suitable for 1310 nm and 1550 nm single-mode OTDRs. For multimode (850/1300 nm) testing, you would need an OM3 or OM4 launch cable. Contact us if you need multimode options.

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