Why Is My Fibre Optic Loss Reading Too High? Troubleshooting with NOVKER NK281 Malaysia
A high fibre optic loss reading does not always mean that the installed cable is damaged. The problem may come from dirty connectors, defective reference patch cords, incorrect wavelength settings or an improper testing procedure.
The NOVKER NK281 Stable Light Source, used together with a compatible optical power meter, can help technicians measure the total end-to-end loss of a fibre link.
When the result is higher than expected, use a systematic troubleshooting process before replacing the cable.
What Is Considered a High Fibre-Loss Reading?
There is no single loss value that is acceptable for every fibre link.
The expected loss depends on:
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Fibre type
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Cable length
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Testing wavelength
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Number of connectors
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Number of splices
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Splitters and other passive components
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Project specifications
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Required safety margin
The estimated link-loss budget may be calculated as:
Total Expected Loss = Fibre Loss + Connector Loss + Splice Loss + Component Loss + Design Margin
A measured result should be compared with the calculated loss budget or the acceptance limit specified for the project.
Confirm the NK281 and Power Meter Wavelengths
The first check is simple but important: make sure both instruments are using the same wavelength.
Correct setting:
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NK281: 1310nm
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Optical power meter: 1310nm
Incorrect setting:
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NK281: 1310nm
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Optical power meter: 1550nm
An optical power meter applies calibration according to the selected wavelength. If the wavelength is incorrect, the displayed result may not represent the actual optical power accurately.
Repeat this check every time the testing wavelength is changed.
Clean Every Fibre Connector
Contamination is one of the most common causes of excessive optical loss.
Dust, oil and small particles on the connector end face can block or scatter the transmitted signal. A contaminated connector may also transfer dirt to another clean connector.
Before testing:
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Inspect the connector end face when suitable equipment is available.
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Clean the connector using an approved fibre-cleaning tool.
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Allow cleaning fluid to dry before connection.
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Never touch the ferrule end face.
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Clean both sides of an adaptor connection.
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Reinspect the connector after cleaning.
Do not repeatedly disconnect and reconnect a dirty connector. This can damage the polished surface and contaminate the test equipment.
Check the Reference Patch Cords
A damaged reference patch cord can make a good installed link appear defective.
Inspect the test cords for:
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Dirty connectors
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Cracked or damaged ferrules
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Excessive bending
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Loose connector boots
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Damaged cable jackets
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Incorrect UPC or APC connector types
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Poor-quality or unstable connections
Replace the patch cord with a known-good cable and repeat the reference process.
Reference-grade test cords should be protected and reserved for testing rather than used as ordinary network patch cords.
Establish the Reference Again
The reference value must be established correctly before testing the installed link.
Connect the NK281 directly to the optical power meter using the appropriate reference patch cord. Wait for the reading to stabilise, then record the reference or set the power meter to 0dB.
Establish the reference again when:
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A reference patch cord is changed
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An adaptor is changed
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The wavelength is changed
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The connection has been disturbed
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The reading appears inconsistent
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The equipment has been switched off and restarted
An incorrect reference can affect every subsequent measurement.
Confirm the Correct Fibre Core
Multi-core fibre cables can create confusion during testing. The light source may be connected to one fibre while the optical power meter is connected to another.
Possible signs include:
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No received signal
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Extremely low optical power
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An unstable reading caused by signals from an active adjacent fibre
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Unexpected results that change when patching is rearranged
Label both ends clearly and verify the fibre-core identification before starting the test.
Check for Tight Bends
Fibre cables must not be bent below their recommended minimum bending radius.
Common problem locations include:
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Behind a network rack
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Inside a fibre distribution box
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Around cabinet corners
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Under cable-management covers
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Near cable-entry points
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At patch-panel connections
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Under overtightened cable ties
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Inside crowded ceiling routes
Bending loss may be more noticeable at 1550nm than at 1310nm.
If the link passes at 1310nm but shows unusually high loss at 1550nm, inspect the route for tight bends or cable compression.
Inspect Fusion Splices
A poor fusion splice can introduce excessive loss even when the splice appears physically complete.
Possible causes include:
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Incorrect fibre alignment
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Contaminated fibre
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Poor cleaving
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Incorrect splicer settings
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Incompatible fibre types
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Damaged electrodes
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Movement during the fusion process
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Poor splice protection
The NK281 and power meter can confirm that the complete link has excessive loss, but they cannot show which splice is responsible.
Use an OTDR to identify the position and estimated loss of individual events along the fibre.
Check Mechanical Connectors and Splices
Field-installable mechanical connectors can cause high loss when:
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The fibre is not fully inserted.
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The fibre end is poorly cleaved.
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Matching gel is contaminated.
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The connector is reused incorrectly.
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The fibre has moved inside the connector.
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The connector is incompatible with the cable type.
Re-terminate or replace suspected connectors and repeat the loss measurement.
For permanent high-quality installations, fusion splicing may provide more consistent results when performed correctly.
Verify UPC and APC Compatibility
UPC and APC connectors must not be directly mated.
Common connector identification:
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UPC: Usually blue
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APC: Usually green
APC connectors use an angled polished end face. Connecting APC to UPC creates an air gap and poor physical alignment, producing excessive loss and reflectance.
Always check:
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Connector colour
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Adaptor type
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Patch-cord specification
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Equipment-port requirement
Do not rely only on the connector shape because SC/UPC and SC/APC use similar external housings.
Account for Splitter Loss
An optical splitter intentionally divides the optical signal and introduces significant loss.
A link that contains a 1:8, 1:16, 1:32 or 1:64 splitter cannot be assessed using the same expected value as a direct point-to-point fibre.
Before declaring that the link has failed, verify:
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Splitter ratio
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Manufacturer’s insertion-loss specification
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Number of connectors before and after the splitter
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Additional fibre length
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Project loss budget
When troubleshooting an FTTH PON installation, distinguish between controlled light-source testing and the measurement of live PON signals.
Check the Light-Source Operating Mode
For standard loss measurement, the NK281 should normally provide a stable continuous optical output unless the procedure requires a modulated signal.
If the light source is operating in a tone mode such as 270Hz, 1kHz or 2kHz, confirm that the power meter supports and correctly detects that mode.
An incompatible or incorrectly selected operating mode may cause unstable readings.
Check Battery Condition
Low battery power can affect equipment operation and may result in unstable output or display behaviour.
Before starting site work:
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Charge the equipment fully or install fresh batteries.
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Carry a suitable charging cable or spare batteries.
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Check the battery indicator.
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Avoid performing acceptance tests when the instrument is about to shut down.
If the reading becomes unstable after extended use, check the battery before investigating the installed fibre.
Compare 1310nm and 1550nm Results
Dual-wavelength testing can help narrow down the problem.
High loss at both wavelengths
Possible causes include:
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Dirty connectors
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Poor splice
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Damaged cable
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Faulty patch cord
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Incorrect reference
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Excessive connector loss
Much higher loss at 1550nm
Possible causes include:
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Tight bends
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Cable compression
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Poor cable routing
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Fibre trapped inside an enclosure
No signal at either wavelength
Possible causes include:
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Complete fibre break
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Wrong fibre core
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Disconnected patching
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Incorrect adaptor
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Light source not transmitting
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Severe connector contamination
Use an OTDR when the fault location cannot be determined through visual inspection and end-to-end testing.
When Should You Use an OTDR?
Use an OTDR when you need to determine:
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Distance to a fibre break
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Position of a high-loss splice
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Connector locations
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Reflective events
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Cable length
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Individual event loss
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End of the fibre
The NK281 and optical power meter answer the question:
How much total optical power has been lost?
The OTDR answers:
Where along the fibre did the loss occur?
Professional troubleshooting may require both tests.
Quick Troubleshooting Checklist
When the loss reading is too high:
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Confirm matching wavelengths.
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Clean all fibre connectors.
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Inspect and replace the reference patch cords if necessary.
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Establish the reference again.
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Confirm the correct fibre core.
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Check UPC and APC compatibility.
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Inspect for tight bends and compression.
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Account for splitter loss.
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Repeat the test at another wavelength.
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Use an OTDR to locate the abnormal event.
Record the results before and after corrective work to confirm that the repair has improved the link.
NOVKER NK281 Applications
The NK281 is suitable for:
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FTTH installation and maintenance
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Fibre optic contracting
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Data centre cabling
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Factory fibre networks
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Building backbone testing
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Campus fibre systems
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CCTV fibre transmission
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Telecom maintenance
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RJ45 and fibre field work
Its combination of stable optical output and network-cable testing functions makes it practical for technicians working with mixed fibre and copper infrastructure.
Contact MTM Precision
Contact us for the NOVKER NK281 Stable Light Source, optical power meters, VFLs, fibre identifiers, OTDRs and fibre optic troubleshooting equipment in Malaysia.
MTM Precision Sdn Bhd
No. 29-1 & 29-2, Jalan Bandar 18,
Pusat Bandar Puchong,
47160 Puchong, Selangor, Malaysia.
Website: www.mtmpre.com.my
WhatsApp: +6016-660 7346
Email: mtmpre@yahoo.com
04 Sep 2026
