RBSE SS Voc Telecom common mistakes
RBSE SS Voc Telecom · Understand the traps and how to avoid them.
Treating Ohm's law and power calculations as pure formula recall and plugging numbers in without checking whether the circuit is series or parallel first.
Candidates memorise V = IR and P = VI but practise mostly on single-resistor examples, so on combined circuits they add resistances that should be combined reciprocally, or apply the supply voltage across each parallel branch incorrectly.
What to do instead
Before any calculation, redraw the circuit and label it as series, parallel or mixed. In series, current is common and voltages add; in parallel, voltage is common and currents add. Then compute equivalent resistance, total current, and branch values in that order, and sanity-check that total current equals the sum of branch currents.
Confusing the units and prefixes used for signal power, attenuation and frequency (dB versus dBm, MHz versus kHz, and the meaning of a negative dB value).
Learners treat dB as an absolute unit and cannot explain why a loss is negative or why dBm has a reference. Prefix arithmetic is done casually, so 2.4 GHz is written as 240 MHz.
What to do instead
Build a one-page reference: dB is a ratio (10 log P1/P2 for power), dBm is power relative to 1 mW, and a loss is a negative dB figure. Practise converting between kHz, MHz and GHz and between mW and dBm until the direction of the sign is automatic, then apply it to a link-budget style question.
Mixing up the roles of local loop, exchange, trunk and subscriber numbering when tracing a call, and assuming every call is set up the same way regardless of distance.
The PSTN is taught as a diagram rather than a sequence, so candidates cannot say which part performs digit analysis, which carries inter-exchange traffic, and where charging and routing decisions happen.
What to do instead
Learn the call as an ordered story: off-hook, dial tone from the local exchange, digits received and analysed, route selected (local, tandem or trunk), ringing, answer, conversation, release and billing. For each stage, name the equipment and the interface it crosses, and practise tracing one local and one long-distance call end to end.
Treating broadband speed, bandwidth and throughput as interchangeable, and ignoring the effect of contention ratio, line attenuation and Wi-Fi on the delivered speed.
Marketing figures dominate everyday language, so candidates repeat 'bandwidth equals speed' and cannot explain why a customer on a 100 Mbps plan measures 40 Mbps.
What to do instead
Separate the terms explicitly: bandwidth is capacity, throughput is achieved rate, latency is delay. Then list the layers where throughput is lost (access line sync rate, contention, CPE, Wi-Fi, server). Practise diagnosing a slow-broadband complaint by testing at each layer in order rather than blaming the ISP immediately.
Confusing cellular concepts such as cell, sector, handover, channel reuse and the function of the antenna gain and tilt when answering RF questions.
These terms are learned as vocabulary lists without a physical picture, so candidates cannot predict what happens to coverage when downtilt is increased or why frequency reuse needs distance between co-channel cells.
What to do instead
Draw a three-sector site with a reused cluster around it, then reason about each parameter: more downtilt reduces cell edge reach and interference; higher gain concentrates energy in a narrower beam; handover transfers the link as the mobile crosses a boundary. Answer RF questions by referring back to that sketch.
Mixing up single-mode and multimode fibre, their typical wavelengths and core sizes, and which test instrument measures loss versus locates a fault.
Candidates memorise 'single mode is faster' without the numbers, and treat the power meter and OTDR as interchangeable, so they choose the wrong tool or the wrong wavelength for a loss test.
What to do instead
Anchor the facts: single-mode has a small core (about 9 micrometres), carries long-haul traffic at 1310 and 1550 nm; multimode has a larger core (50 or 62.5 micrometres) for short links. A light source plus power meter gives end-to-end loss; an OTDR gives a distance trace showing splices, connectors and breaks. Match the tool to the question asked.
Describing installation and jointing steps in the wrong order, or omitting the preparatory and verification steps such as cleaning, splice-loss checking and sealing before closure.
Practical work is learned by watching, so the written sequence is reconstructed from memory and steps like stripping length, fibre cleaning, and re-measuring loss after closure are dropped.
What to do instead
Write each procedure as a numbered checklist with a verification step at the end: prepare and clean, splice or terminate, measure loss, seal and label, then record results. Rehearse the checklist aloud for splicing, copper jointing and CPE installation so the order becomes fixed.
Jumping to a component replacement on a fault report instead of following a structured diagnostic sequence from the customer premises inward.
Candidates answer with the most dramatic possible cause (cable cut, card failure) because they have not practised narrowing, and they skip confirming the reported symptom and checking the simple causes first.
What to do instead
Use a fixed sequence: confirm and reproduce the fault, check power and CPE indicators, test at the demarcation point, then work outward to the access network. Eliminate half the possibilities at each step, and state the evidence that would confirm or reject each candidate cause in the answer.
Answering safety questions with general statements about being careful rather than naming the specific hazard control, such as isolation and lock-off before work, treating every fibre as live, or using the correct ladder and PPE for the task.
Safety is revised last and treated as common sense, so candidates cannot recall the mandatory controls for electrical work, laser exposure, working at height, or chemical and battery handling.
What to do instead
Memorise controls by hazard: electrical (isolate, prove dead, lock off, earth), optical (never look into a fibre or connector, use a power meter, dispose of shards), height (inspect and foot the ladder, three points of contact), chemical (ventilation, gloves, eye protection, spill kit). Attach each control to a real task you have seen and state the consequence of skipping it.
Treating the entrepreneurship and employability section as opinion questions, giving vague answers about hard work instead of naming concrete business, costing or customer-service concepts.
Candidates focus revision on technical domains and do not prepare vocabulary such as fixed and variable cost, break-even, quotation, service-level commitment, or the difference between a franchise and an independent service business.
What to do instead
Prepare a small set of worked examples: a one-page cost sheet for a cable-laying job, a break-even calculation, a short customer complaint resolution script, and a list of the licences and registrations a telecom contractor needs. Answer these questions with named concepts and a number or a step, not with attitude statements.