4-11
Extech Reporter
UNIT 4
System Reference Power
(shown as Minimum Required Power on Circuit Detail Reports)
Definition: the optical power level that determines whether a link passes or fails; a.k.a. Pass/Fail
threshold. If the Measured Power is greater than the System Reference Power, the link will show PASS;
likewise, if the Measured Power is less than the System Reference Power, the link will show FAIL.
NOTE: link measurements that are marginal (meaning that they are close to the System Reference
Power, within the accuracy of the test equipment) should be evaluated further.
Units: dBm
Calculation: (Light Source Reference Power) + (Total Allowable System Loss)
Total Allowable System Loss
Light
Source
Reference
Power (dBm)
INVALID
OPERATING
MARGIN **
Minimum
Required
Power (dBm)
Measured
Power (dBm)
PASS
OPERATING MARGIN
or
SYSTEM OVERHEAD
Optical Loss
FAIL
Total Allowable System Loss
Definition: the total amount of optical loss attributed to the passive components of the link (i.e. Fiber
Loss, Connection Loss, and Splice Loss). Total Allowable System Loss is also known as a Link Budget.
For generic cabling standards such as the TIA 568 or the ISO/IEC 11801, link budgets are calculated
based upon the actual configuration of the link under test. Some standards (e.g. various Ethernets) have
pre-defined link budget loss values based upon the upper limits of the link configuration.
Units: dB
Calculation: (Fiber Loss) + (Connection Loss) + (Splice Loss)
Total Allowable System Loss
Light
Source
Reference
Power (dBm)
INVALID
OPERATING
MARGIN **
Minimum
Required
Power (dBm)
Measured
Power (dBm)
PASS
OPERATING MARGIN
or
SYSTEM OVERHEAD
Optical Loss
FAIL
Interpreting Extech Reporter Screens and Reports, cont.
