Punjab PSEB Matric NSQF Telecom (Optical Fiber Splicer) common mistakes
Punjab PSEB Matric NSQF Telecom (Optical Fiber Splicer) · Understand the traps and how to avoid them.
Treating 1310 nm and 1550 nm as interchangeable test wavelengths, and quoting a single 'typical loss' figure for a fibre link without stating the wavelength it applies to.
Candidates memorise one loss-per-kilometre number and one 'OTDR range' figure, then apply it to every question. They do not internalise that 1310 nm sits near the zero-dispersion point and has higher attenuation (~0.35 dB/km) while 1550 nm has lower attenuation (~0.20–0.25 dB/km) but higher dispersion, and that splice loss and connector loss also vary with wavelength.
What to do instead
Build a two-column mental table: 1310 nm and 1550 nm, each with attenuation per km, typical splice loss and typical connector loss. In every numerical answer, write the wavelength as part of the unit, e.g. '0.25 dB/km at 1550 nm'. When a question gives a link budget without a wavelength, state the assumption explicitly before calculating.
Mixing up single-mode and multimode fibre by core size and then choosing the wrong splice method, connector or source for the scenario described.
The numbers 9 µm, 50 µm and 62.5 µm get memorised as a list without being tied to behaviour. Candidates then accept a question about splicing 50 µm multimode to single-mode fibre as if it were routine, or recommend a laser source and long-haul OTDR settings for a short multimode LAN link.
What to do instead
Anchor each fibre type to a use case: 9/125 µm single-mode for long haul, FTTx and PON; 50/125 µm and 62.5/125 µm multimode for short building and data-centre links with LED/VCSEL sources. Learn that joining different core sizes gives high, unpredictable loss and is not a normal field practice. Practise classifying a scenario by distance, bit rate and source before answering.
Reciting the 12-fibre colour code in the wrong order or confusing the fibre position colour with the unit/tube colour, especially around blue, turquoise/aqua and the second group.
Candidates learn the sequence as a chant but never separate the two layers of coding: the colour of the fibre within its tube and the colour of the tube within the cable. Under exam pressure the two lists merge, and standard versus alternative colour schemes are blended.
What to do instead
Write out the 12-position sequence from memory twice a day and pair it: position 1 blue, 2 orange, 3 green, 4 brown, 5 slate/grey, 6 white, 7 red, 8 black, 9 yellow, 10 violet, 11 rose/pink, 12 aqua/turquoise. Then practise reading a cable description as 'tube colour X, fibre colour Y = fibre number...' and compute the absolute fibre count as (tube number − 1) × 12 + fibre number. State clearly which scheme the question uses before answering.
Answering safety questions with generic statements ('wear PPE', 'be careful with chemicals') instead of naming the specific hazard control for the task, such as the correct eyewear for a live fibre or the disposal route for a bare fibre offcut.
Safety is studied as a list of slogans rather than as task-linked procedures. Candidates do not connect the hazard to the control: invisible 1310/1550 nm radiation versus a visible red fault-locator source, skin and eye contact with isopropyl alcohol, or the splinter risk from cleaved fibre ends.
What to do instead
For each task in the splicing workflow, write one line: hazard, control, evidence. Examples: never look into a fibre or connector without confirming the source is off and using a power meter; use a visible fault locator only for finding breaks, not for eye-safe verification; use alcohol in a ventilated area away from ignition sources; collect cleaved offcuts in a sealed sharps container, never on the bench or floor. Learn that laser safety eyewear is wavelength-specific and that ordinary safety glasses are not a substitute for procedure.
Describing stripping and cleaning in the wrong order or with the wrong consumable, e.g. cleaning the bare fibre after cleaving with a dry tissue, or using the cleaver to score through the coating.
The steps are memorised as a sequence of verbs without the reason behind each one. Candidates do not realise that residue left on the bare fibre prevents a clean cleave and causes bubbles or loss in the splice, and that the cleaver blade is for the glass, not the coating.
What to do instead
Lock in the order: remove outer sheath and strength members, expose the buffer/coating, strip coating with the correct-size stripper, clean the bare glass with lint-free tissue and appropriate alcohol, then cleave on a dedicated cleaver. Learn the acceptance check: end angle within tolerance (typically under about 1 degree for good fusion splicing) and no chips, lips or mist. Reject and re-cleave rather than trying to 'splice through' a bad end face.
Choosing mechanical splicing over fusion splicing (or vice versa) without justifying it by environment, loss budget and volume, and describing fusion splicing as simply 'joining two fibres with heat'.
Candidates learn a definition but not the decision criteria. They miss that fusion splicing gives lower loss and higher long-term reliability and suits permanent joints, while mechanical splicing needs no power and suits emergency or low-volume work but has higher loss and needs index-matching gel and a protected housing.
What to do instead
Prepare a comparison table with rows for typical loss, equipment needed, power requirement, skill, repeatability, environment and cost per joint. Then practise short scenario answers: 'rural FTTx distribution joint, 200 splices, mains power available' leads to fusion; 'single emergency repair in a flooded chamber, no power' leads to mechanical with a proper splice protector. Always state the trade-off, not just the choice.
Reporting a splice loss figure straight from the fusion splicer display as the final measured value, and treating an estimated loss reading as a calibrated measurement.
The splicer's estimate is convenient and looks authoritative. Candidates do not know it is derived from alignment and camera data, not from optical measurement, and can differ from the true loss. They also confuse splice loss with total link loss and forget that a bi-directional OTDR reading is needed because of gainers and directional effects.
What to do instead
State the hierarchy explicitly: splicer estimate is for process control only; the acceptance value comes from OTDR measurement, ideally averaged from both directions, or from a power meter and source for end-to-end loss. In calculations, separate splice loss, connector loss and fibre attenuation, then sum them. When asked for a splice loss value, say how it was measured and quote the method.
Reading an OTDR trace as if every upward step were a fault, and setting the wrong range, pulse width or refractive index for the fibre under test.
Candidates learn the OTDR screen as a picture rather than as a measurement with settings. They do not recognise that a reflective spike is a connector or mechanical joint, a non-reflective step is a fusion splice, a downward step can be a 'gainer' caused by mismatched backscatter, and that a wrong refractive index shifts every distance reading.
What to do instead
Learn the four trace signatures: end of fibre, reflective event, non-reflective event, and gainer. Before interpreting a trace, confirm the settings: correct refractive index for the fibre type, pulse width suited to the distance, and range set beyond the link length. Practise reading a described trace as a sequence of events and converting event positions to distances, and always state that a suspected bad splice should be re-measured from the far end before being condemned.
Describing closure sealing and cable management in general terms, without specifying strength-member anchoring, bend radius, slack storage and the direction of sealing (tape, heat-shrink, gasket) for the closure type named in the question.
Closures are studied as a labelled diagram, so candidates remember 'it protects the splice' but not the mechanical logic. They forget that the strength members carry the tensile load, that the splice tray must keep fibres above the minimum bend radius, and that a poorly seated gasket or wrongly wrapped sealing tape is the usual cause of water ingress.
What to do instead
Learn closures as a load path plus a water path. Load: sheath opened to the correct length, strength members and central member secured to the closure anchor, buffer tubes routed with slack in the tray, bend radius respected. Water: gasket clean and seated, sealing tape or heat-shrink applied in the specified direction and sequence, unused ports blanked. Practise describing a specific closure type end to end, including the final pressure or visual check.
Confusing the roles and signal directions in a PON - saying the OLT receives the upstream signal from the ONT, or mixing up downstream 1490 nm and upstream 1310 nm - and ignoring split ratio and power budget when judging whether an ONT will come online.
The PON is memorised as a diagram of boxes rather than as a directional system with a shared upstream and a broadcast downstream. Candidates then cannot reason about why a splitter loss or a long drop causes a weak ONT receive level, or why one ONT's transmitter cannot be heard over another's.
What to do instead
Draw the PON as arrows: OLT downstream transmit at 1490 nm through the splitter to all ONTs; ONT upstream transmit at 1310 nm through the same splitter to the OLT, arbitrated by time slots. Add typical splitter losses (1:2 about 3.5 dB, 1:4 about 7 dB, 1:8 about 10.5 dB, 1:16 about 14 dB, 1:32 about 17.5 dB) and use them in a power-budget sum from OLT launch power to ONT receive sensitivity. Practise deciding whether a described fault is fibre, splitter, connector or ONT by the numbers.