Punjab PSEB Sr. Sec. NSQF Telecom (Optical Fibre Technician) common mistakes
Punjab PSEB Sr. Sec. NSQF Telecom (Optical Fibre Technician) · Understand the traps and how to avoid them.
Treating dB and dBm as interchangeable in loss-budget questions, e.g. writing a received power of '-3 dB' or adding a 20 dBm source to a 3 dB loss and answering '17 dBm of loss'.
Candidates memorise the link-budget formula without fixing the unit semantics; dBm is an absolute power referenced to 1 mW and dB is a ratio, so adding and subtracting them produces a power in dBm while losses and gains stay in dB. Under exam pressure the labels get swapped because both appear in the same arithmetic string.
What to do instead
Before any calculation, label every number with its unit and check the dimensional chain: dBm minus dB gives dBm, dBm minus dBm gives dB, dB plus dB gives dB. Practise ten mixed problems where the answer must state units explicitly, and reject any option that reports a loss in dBm or a received power in dB.
Reading the wrong window or wavelength on a two-window power meter or light source, and quoting a splice loss measured at 1310 nm as if it were the 1550 nm figure (or vice versa), without stating the test wavelength.
Loss is wavelength-dependent (Rayleigh scattering falls as wavelength rises while macrobend and OH-absorption losses behave differently), and candidates treat 'loss' as a single fixed property of a component. Instrument default settings and the last-used configuration also carry over silently in lab and field kits.
What to do instead
Always write the test wavelength next to every measured value and confirm source and meter are on the same window before zeroing. Learn the typical directional differences: 1550 nm shows higher macrobend sensitivity, 1310 nm shows higher Rayleigh loss. In numerical answers, state the wavelength as part of the result.
Misreading OTDR traces: calling a reflective spike a splice, ignoring the dead zone after the front-panel connector, or reporting the end-of-fibre reflection as a break when it is simply the far-end Fresnel reflection.
Candidates learn the trace shape by picture-matching rather than by cause: reflection comes from a refractive-index step (connector, mechanical splice, cleaved end), loss without reflection comes from fusion splices and bends. The launch dead zone hides the first events, and the far-end spike looks dramatic enough to be mistaken for a fault.
What to do instead
Build a cause-to-signature table and apply it in order: spike plus loss equals connector or mechanical splice; step loss with no spike equals fusion splice or bend; sudden trace end with strong spike equals far end or clean break; gradual slope change equals macrobend or high-loss section. Always note the event distance, the dB loss, and the reflectance, and check the dead-zone specification against the pulse width chosen.
Confusing single-mode and multimode practice: applying 1310/1550 nm testing and tight bend radii to multimode, quoting 50/125 as the cladding diameter, or assuming a visible red VFL will show a fault in a buried single-mode link end-to-end.
Core/cladding dimensions (9/125, 50/125, 62.5/125) are memorised as strings without a mental picture of the fibre cross-section, and VFL behaviour is assumed rather than reasoned from attenuation and bend-loss physics.
What to do instead
Draw the cross-section once for each fibre type with core, cladding, coating and buffer diameters labelled, and attach the standard operating windows to each type. Remember the VFL is a short-reach continuity and bend-finding aid at 650 nm: it will not pass far down a long single-mode span. Answer fibre-type questions by naming core/cladding in micrometres first.
Getting the 12-fibre colour code out of order, especially swapping the position of blue/green or omitting the standard sequence in tube and fibre counting, and then mis-identifying a fibre during splicing or documentation.
The sequence is learned by rote as a song rather than as an indexed list, and candidates do not distinguish the fibre colour within a tube from the tube colour itself, so counting errors compound when a cable has multiple tubes.
What to do instead
Write the sequence as a numbered table (1 blue, 2 orange, 3 green, 4 brown, 5 slate, 6 white, 7 red, 8 black, 9 yellow, 10 violet, 11 rose, 12 aqua) and practise identifying 'tube 3, fibre 7' style references. Always state whether you are counting tubes or fibres, and confirm the count direction from the cable end marking before splicing.
Describing a splice procedure that skips mandatory steps: cleaving without checking the cleave angle, opening the fusion splicer wind cover before the arc completes, or forgetting to set the splice mode/programme for the fibre type before arc.
Candidates recall the headline 'strip, clean, cleave, splice, protect' and treat the quality checks as optional detail, because those checks are not visible in a written summary of the process.
What to do instead
Learn the procedure as a checklist with acceptance criteria attached: strip length per holder, wipe with lint-free tissue and alcohol, cleave angle within the splicer's limit (typically under about 1 degree for good results), estimated loss checked on screen, then heat-shrink protection centred over the splice with no bubbles or trapped fibre. Rehearse the checklist in writing until the acceptance numbers come out automatically.
Quoting a single generic bend radius for all cables and situations, e.g. 'never bend fibre tighter than 30 mm', instead of the installed-versus-during-pull distinction and the manufacturer's stated minimum.
The rule is remembered as a slogan, not as two separate limits (a tighter limit during installation, a looser one in permanent service), and candidates do not connect macrobend loss to the 1550 nm window where it bites hardest.
What to do instead
State both limits with their context: minimum bend radius during installation is typically a multiple of the cable outer diameter (commonly around 20 times OD for long-term and roughly 10-15 times during a controlled pull, per manufacturer data), and permanent bends must respect the datasheet. Add the consequence: excessive bending causes macrobend loss that is worse at longer wavelengths and can be seen as a loss step on an OTDR trace.
Answering FTTH questions with a generic 'install the ONT and test it' instead of the specific sequence: power level at the ONT, connector cleanliness and inspection, bend management in the drop cable and ONT tray, and confirming service with the correct upstream/downstream readings.
Customer-premises work is learned from watching rather than from a structured procedure, so the steps that prevent callbacks (inspection, cleaning, strain relief, loss verification against the design budget) are omitted from written answers.
What to do instead
Memorise the commissioning sequence as a numbered list ending in measured evidence: receive power within the ONT's specified window, no visible contamination on the connector end-face, drop cable secured with correct bend radius, and the reading recorded on the job sheet. Include the fault-isolation order (ONT reading, patch cord, drop, splitter, feeder) when asked about a no-service complaint.
Treating documentation and restoration as afterthoughts: no as-built record of splice loss, fibre assignment, or route, and a restoration answer that jumps straight to re-splicing without first confirming the fault location and spare capacity.
Candidates separate 'technical' work from 'paperwork' and do not see that records are what make fast restoration possible; exam scenarios reward the diagnostic sequence, not the repair action alone.
What to do instead
Learn restoration as locate, isolate, confirm, repair, retest, record: use OTDR and power meter results to fix the fault distance, check records for spare fibres and tube assignments, then splice and re-measure against the original baseline. Practise writing a one-line as-built entry (route, cable, tube, fibre, splice loss, date, tester) so documentation answers carry the same specificity as technical ones.
Giving vague safety and tool-handling answers: 'handle chemicals carefully' or 'wear PPE' without naming the specific hazard controls for bare fibre offcuts, alcohol-based cleaning fluids, and fusion splicer electrodes.
Safety is studied as a list of nouns rather than as hazard-control pairs, and the sharpest real risks in OFC work (fibre shards in skin and eyes, flammable cleaning solvents, arc and hot electrodes, laser exposure) are not linked to their controls.
What to do instead
Rewrite each safety point as hazard plus control plus disposal: bare fibre offcuts go into a sealed sharps container and are never left on the bench or in clothing; alcohol wipes are used away from the arc and stored sealed; the splicer is powered down before electrode work; laser sources are never viewed directly and connectors are capped. Pair every tool with its inspection habit, such as checking the cleaver blade and waste bin before each shift.