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ETA · Last updated November 2026

ETA OTDR Testing Specialist (OTS): free practice test

OTS is ETA's stand-alone specialist certification for OTDR testing: set-up, operation, trace analysis and maintenance of OTDRs, plus related test equipment, for premises, outside plant, FTTx and PON links. The written exam has 25 questions in 2 hours with a 75% pass mark, after a hands-on OTDR course and skills exam at an ETA-approved school. This prep covers only the written exam.

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About the ETA OTS exam

OTS is ETA's stand-alone specialist certification for OTDR testing: set-up, operation, trace analysis and maintenance of OTDRs, plus related test equipment, for premises, outside plant, FTTx and PON links. The written exam has 25 questions in 2 hours with a 75% pass mark, after a hands-on OTDR course and skills exam at an ETA-approved school. This prep covers only the written exam.

What's on the exam

ETA OTS
Fiber Optic Safety for OTDR Work
8 key facts
Transmission, Decibels and Light Principles
8 key facts
Fiber Construction and Characteristics
8 key facts
Connectors, Endfaces and Reflectance
9 key facts
Related Test Equipment and Loss Testing
8 key facts
OTDR Operation and Settings
8 key facts
OTDR Trace Analysis and Dead Zones
8 key facts
Launch and Receive Cables and Link Measurement
7 key facts

Each branch is a topic in the official outline. Members see every key fact on the full mind map. Read the free study guide →

How to pass the ETA OTS exam

  • Each of the 25 questions is worth 4%, so 7 wrong answers means a fail. With almost 5 minutes per question, sketch the trace for any OTDR scenario before choosing.
  • Over half of the competency list is background: safety, light, fiber, connectors and loss test sets. Don't study only OTDR traces.
  • Know the named standards: TIA-526-14 one, two and three test jumper references (Annexes A, C and B), Telcordia GR-326 endface geometry, IEC 61300-3-35 inspection and TIA-568 loss and reflectance limits.
  • For every OTDR setting (wavelength, pulse width, index of refraction, averaging, auto versus manual), learn what it changes on the trace and the trade-off it brings.

Save your results and get your Readiness Score

Create a free account after the test: your score by topic, a mistakes bank, the complete study notes for the first topic, flashcards and the RCDD Numbers & Formulas Sheet.

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What's in the premium ETA OTS prep

Premium ETA OTS prep is studied one topic at a time. Each step starts with that topic's key notes and flashcard deck, then its own question sets of 25, so you master one topic before you move to the next. When every topic is strong, the 6 full mock exams show you're ready.

3,000practice questions, every answer explained
6full-length mock exams, 50 questions each, timed
800flashcards with spaced repetition, sorted by topic
60comprehensive key notes across 8 topics

Your step-by-step study path

  1. 1
    Fiber Optic Safety for OTDR Work8 key notes, 100 flashcards, then 375 practice questions in 15 sets of 25
    Notes free with an account
  2. 2
    Transmission, Decibels and Light Principles8 key notes, 100 flashcards, then 375 practice questions in 15 sets of 25
    Premium
  3. 3
    Fiber Construction and Characteristics8 key notes, 100 flashcards, then 375 practice questions in 15 sets of 25
    Premium
  4. 4
    Connectors, Endfaces and Reflectance8 key notes, 100 flashcards, then 375 practice questions in 15 sets of 25
    Premium
  5. 5
    Related Test Equipment and Loss Testing7 key notes, 100 flashcards, then 375 practice questions in 15 sets of 25
    Premium
  6. 6
    OTDR Operation and Settings7 key notes, 100 flashcards, then 375 practice questions in 15 sets of 25
    Premium
  7. 7
    OTDR Trace Analysis and Dead Zones7 key notes, 100 flashcards, then 375 practice questions in 15 sets of 25
    Premium
  8. 8
    Launch and Receive Cables and Link Measurement7 key notes, 100 flashcards, then 375 practice questions in 15 sets of 25
    Premium
  9. Final step: 6 full mock exams50 questions each, timed like test day. Pass them, then book your exam.
    Premium
Free with an account

Read the complete ETA OTS study notes for “Fiber Optic Safety for OTDR Work”

Our first full set of comprehensive notes, about 12 minutes of reading: Laser classes and the OTDR · Safe inspection · Handling OTDRs and working near live networks · OSHA and electrical hazards, a worked exam example, the traps examiners use and a one-minute recap. Create a free account to read it and see how premium notes work before you decide.

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Study tools included

3,000 practice questions

3,000 exam-style questions per exam, organized topic by topic in sets of 25. Every answer explained, with the rule it comes from.

6 full mock exams

6 full-length timed mock exams per exam, with real question counts and time limits, so test day feels like practice day.

Exam Readiness Score

One 0 to 100 number that tells you when you're ready to book. Reach 80 and you're covered by our Pass Guarantee.

800 flashcards + spaced repetition

800 flashcards per exam, in a deck for each topic, that come back right before you'd forget them. Five minutes a day keeps every number fresh.

60 comprehensive key notes

60 key notes per exam, split across its topics and each explained in full: the concepts, worked exam examples, the traps examiners use and a quick recap. Your first set is free with an account.

Mind maps

See the whole exam on one screen: every topic and the facts under it.

Sample questions with answers

These are the questions in the free test above, with answers. Try the test first. You'll learn more by getting some wrong.

1. A technician wants to check whether an OTDR port is emitting by looking into it through an optical (eyepiece) fiber microscope. Why is this unsafe?
Answer: It focuses invisible infrared light into the eye. Telecom OTDR wavelengths are infrared and invisible, and an optical microscope collects and magnifies that light straight into the eye with no blink reflex. Use a video inspection probe, or confirm output with a power meter, and only inspect ports with the source off. Single-mode lasers are a hazard too.
2. A source launches -5 dBm into a link and the power meter reads -18 dBm at the far end. About what share of the launched power arrives?
Answer: 5%. Loss is -5 - (-18) = 13 dB. A 10 dB loss leaves 10% and each further 3 dB roughly halves the power, so 13 dB leaves about 5% (10 to the power -1.3 = 0.05). Don't read the dB number as a percentage; 3 dB is 50% and 20 dB is 1%.
3. Why does light escape from the core of a fiber at a tight macrobend?
Answer: Rays hit the boundary below the critical angle. Total internal reflection only works when light hits the core-cladding boundary beyond the critical angle measured from the normal. A tight bend steepens the angle at the outer side so it falls below the critical angle and light refracts into the cladding and is lost. Longer wavelengths spread more into the cladding, so they lose more at bends.
4. On a 50/125 µm multimode link, the OTDR shows a steeper fiber slope at 850 nm than at 1300 nm. What explains this?
Answer: Rayleigh scattering is much greater at shorter wavelengths. Rayleigh scattering varies roughly with 1 over wavelength to the fourth power, so multimode fiber loses about 3 dB/km at 850 nm against about 1 dB/km at 1300 nm. The OTDR slope shows that attenuation. Dispersion spreads pulses but doesn't change the trace slope, and the water peak is near 1383 nm.
5. A G.657 fiber data sheet describes a trench-assisted index profile. Where is the trench, and what does it do?
Answer: A low-index cladding ring that holds light in at bends. The optical trench is a ring of lower refractive index placed in the cladding just outside the core. At a tight bend it reflects escaping light back toward the core, which is how bend-insensitive single-mode and multimode fibers keep bend loss low. It's part of the glass profile, not the coating.
6. An OTDR reports -28 dB reflectance at a single-mode UPC mated pair. The project uses the ANSI/TIA-568 limit of -35 dB for single-mode. What is the result?
Answer: Fail, because -28 dB reflects more light than the -35 dB limit. Reflectance is a negative number, and the closer it is to zero, the more light is reflected. -28 dB is worse than -35 dB, so the pair fails; inspect, clean and retest, and replace a damaged connector. TIA-568 sets loss and reflectance limits separately, so a pair can fail on either one.
7. Single-mode factory jumpers from one batch show poor return loss, yet their endfaces look clean and undamaged under a video microscope. What test is most likely to find the cause?
Answer: An interferometer check to Telcordia GR-326. An interferometer measures radius of curvature, apex offset and fiber undercut or protrusion. Out-of-spec geometry, such as an undercut fiber or large apex offset, stops the cores touching and creates an air gap that reflects light. A video microscope only shows surface cleanliness and damage, not geometry.
8. A fiber break is suspected about 3 m beyond a patch panel, inside the OTDR's dead zone even with its shortest pulse. Which tool locates it fastest?
Answer: A visual fault locator (red light). A visual fault locator injects bright visible red light that glows through the jacket or buffer at a break, a tight bend or a bad connector within its range of a few kilometres, which is ideal close to the panel. A longer pulse widens the OTDR dead zone. A power meter only confirms loss, not where it is.
9. Before disconnecting a fiber in a working patch panel, a technician must confirm whether it carries live traffic without interrupting service. Which tool is used?
Answer: A clip-on fiber identifier. A clip-on fiber identifier puts a slight macrobend in a buffered fiber or patch cord and detects the leaking light, showing traffic, its direction and any test tone without disconnecting. An OTDR, OLTS or VFL all need the fiber opened and could disrupt the service. Treat any fiber as live until checked.
10. A 300 m data center link has connector pairs only 5 m apart at each patch panel. On the OTDR in automatic mode, each pair of connectors shows as a single merged event. What change resolves them?
Answer: Switch to manual mode with the shortest pulse width. A short pulse narrows the event dead zone, so closely spaced reflective events show separately. Auto mode often picks a longer pulse to reach the fiber end. A longer pulse merges events further, averaging affects noise not resolution, and a wrong index only shifts distances.
11. The OTDR trace of a long outside plant span is noisy near the far end, making a small splice hard to measure. The pulse width already suits the event spacing. What should the technician do?
Answer: Increase the averaging time. Averaging more acquisitions lowers the random noise on the trace, improving the signal-to-noise ratio far down the span without changing resolution. Real-time mode shows a fast but noisy trace for live checks, and a shorter pulse adds noise. The index of refraction only scales distance.
12. An OTDR shows a non-reflective event at 4.2 km with 0.04 dB loss at 1310 nm but 0.85 dB at 1550 nm. What is the most likely cause?
Answer: A macrobend in the cable or a splice tray. Bend loss rises steeply with wavelength because the longer wavelength's mode field spreads further into the cladding. A splice or MFD mismatch loss is similar at both wavelengths, and a connector pair would also be reflective. Check slack loops, closures and trays at that distance, and test at 1625 nm if available.
13. Two reflective connector pairs 1.5 m apart show as one reflective spike on the trace. Which OTDR specification describes this limit?
Answer: Event dead zone. Event dead zone is the minimum distance after a reflective event at which a second reflective event can be seen as separate. Attenuation dead zone is longer: the distance before the loss of a following event can be measured. Dynamic range sets how much loss the OTDR can see through, not how close events can be.
14. A technician fits a 20 m launch cable and uses a 1 µs pulse to test a 2 km link. The first link connector cannot be measured. Why?
Answer: The launch cable is shorter than the attenuation dead zone. A launch cable must be long enough for the trace to recover from the OTDR's own connector reflection before the first link connector, so it must exceed the attenuation dead zone at the pulse used. A 1 µs pulse is about 200 m long in the fiber, far beyond 20 m. Use a longer launch cable or a shorter pulse; a receive cable is needed for the far-end connector.
15. A link is tested with launch and receive cables. Where are the OTDR's end-to-end loss markers placed so that the result includes both end connectors?
Answer: On the launch and receive cable backscatter, outside the end connectors. Placing markers on the backscatter of the launch cable just before the first link connector and of the receive cable just after the last one includes both end connections, the fiber and any splices. Markers inside the link leave out the end connectors, and the trace start and end add the test cables and the OTDR port.

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ETA OTS exam FAQ

How many questions are on the ETA OTS exam?

25 multiple-choice questions, with a time limit of 2 hours. Format: closed book; scratch paper and a non-programmable calculator are allowed. eta requires an otdr testing course and hands-on skills exam at an eta-approved school, so this prep covers only the written knowledge exam.

What is the passing score for ETA OTS?

75%.

How much does the ETA OTS exam cost?

US$155 for the exam, with one free retake within one year of the first sitting; course and hands-on fees are set by the school. Certification term 4 years, with maintenance required. BICSI fees can change without notice, so confirm on bicsi.org before you apply.

Which languages is the ETA OTS exam offered in?

English. ETA does not list other languages for OTS; confirm with ETA or your school.

Where do I take the ETA OTS exam?

ETA-approved fiber training schools with an ETA Course Approval, which run the required OTDR testing course and hands-on skills exam; the written exam is proctored by an ETA Certification Administrator online (Trapeza) or on paper.

Is this ETA OTS practice test free?

Yes. The 15-question practice test on this page is free, with an explanation for every answer and no signup. A free account also unlocks the complete study notes for the first topic. The full ETA OTS prep is Premium at $147 a month for this exam.

What's in the premium ETA OTS prep?

3,000 practice questions organized topic by topic (Fiber Optic Safety for OTDR Work: 375; Transmission, Decibels and Light Principles: 375; Fiber Construction and Characteristics: 375; Connectors, Endfaces and Reflectance: 375; Related Test Equipment and Loss Testing: 375; OTDR Operation and Settings: 375; OTDR Trace Analysis and Dead Zones: 375; Launch and Receive Cables and Link Measurement: 375), 6 full-length timed mock exams of 50 questions, 800 flashcards and 60 comprehensive key notes split across all 8 topics, plus a mistakes bank and the Readiness Score.

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Exam details are summarized from the official candidate information available in October 2026. BICSI changes formats and fees, so confirm with ETA International (Electronics Technicians Association), accredited by ICAC under ISO/IEC 17024 before you book. RCDDQuizBank is not affiliated with BICSI or Pearson VUE.

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