When we purchase the OTDR, sometimes we meet the problem: how long this OTDR can test? Today, we share a tip to you:

Take the single mode OTDR with 1310/1550nm as example, in the actual test, the average  loss with 1310nm is near to 0.33dB/KM, the average loss with 1550nm is near to 0.22dB/KM. We know during the test, the fiber quality, connector quality, connecting close or not, etc. all would infect the loss and then final test distance. So to make it more precision, we caculate 1310nm as 0.38dB/KM, 1550nm as 0.3dB/KM.

Here's the formula used to get the distance: OTDR dynamic range÷Loss=Distance.

For example, EXFO OTDR MAX-715B-SM1, 1310/1550nm, 30dB. The testing distance with 1310nm: 30dB÷0.38dB/KM=79KM. The testing distance with 1550nm: 30dB÷0.3dB/KM=100KM. 

Here we see, 1550nm is right for long test because of its low loss. We suggest, constructors test with both 1310nm and 1550nm while working.

Besides the dynamic range on the paper, there's another factor influencing the real test distance: Quality of the inside laser. Poor laser has less power to reach the formula testing distance. Same 30dB on the paper, maybe the final test distance only more or less 40KM. So,if you want to get the true test distance corresponding to the dyanmic range on the paper, better to choose high-quality OTDR.