OTDR Launch Cable Box Guide: Why You Need One and How to Choose 1000m vs 2000m
Quick answer: An OTDR launch cable box (also called a launch fiber or dead zone eliminator) is a spool of known-length fiber placed between the OTDR and the link under test. It moves the first connector out of the OTDR's dead zone so you can measure its loss and reflectance accurately. Choose 1000 m for FTTH and short links, and 2000 m for long-haul testing with longer pulse widths.
What Is the OTDR Dead Zone?
Right after the OTDR fires a pulse, the strong reflection at its front connector saturates the detector. For a short distance the trace is blind, so the first connector and any nearby events cannot be measured. Wider pulse widths create longer dead zones.
How a Launch Cable Box Solves It
With a launch cable in place, the OTDR recovers from saturation before light reaches the link, so the first connector appears as a clear, measurable event. Add a second box at the far end (a receive cable) to measure the last connector too.
1000m vs 2000m: Which Length?
| Length | Best for |
|---|---|
| 1000 m | FTTH, PON drops, campus and data center links, short pulse widths |
| 2000 m | Metro and long-haul, longer pulse widths, high-dynamic-range OTDRs |
Rule of thumb: the launch cable should be longer than the attenuation dead zone at the widest pulse width you plan to use.
How to Set Up a Launch Cable
- Clean and inspect all connectors (see our inspection and cleaning kit).
- Connect OTDR → launch box → link under test (→ receive box).
- Match connector type and polish (APC/UPC); swap OTDR ports with an EXFO swap-out connector if needed.
- Enter the launch length in the OTDR setup so the distance is offset automatically.
- Run the test and read loss at the first and last connectors.
Recommended OTDRs
Pair your launch box with the COMWAY MAX-600-M4, EXFO MAX-715D or budget HSV-110D. Compare them in our 2026 OTDR buying guide, and for quick short-link checks read our VFL guide.
FAQ
Do I really need a launch cable for OTDR testing?
Yes, if you need to measure the first connector. Without it, that connector sits in the dead zone and cannot be characterized.
What fiber is in the launch box?
Our boxes use G652D single-mode fiber with SC, FC, LC or ST connector options.
Can I use one launch box at both ends?
You need two for a full test: one launch and one receive cable, or test from both directions.
Does the launch cable length affect results?
Only the offset. Enter the length in the OTDR so distances are measured from the start of the link.