IDEAL Networks LanTEK III, Руководство пользователя, Страница: 66 / 78

LanTEK III 161809 Iss 2
User Manual Page65
Fig. 81 Return Loss Test
6.12.1 Return Loss Test Error
Same as with loss, an excessive return loss also results in signal reduction at the reception
end. It also indicates that an impedance mismatch exists in a section of the cable. A value of
20 dB or higher indicates a good twisted-pair cable.
6.13 Impedance Test
The average impedance is calculated from delay of electrical signal and capacitance
measurement. The result is indicated in ohm. The average impedance can help in
indentifying damages to cable, connections or cable sections with impedance mismatch.
Since this test uses a capacity measurement, the correct cable type must be indicated to
obtain a precise measuring result.
NOTE:
The measurements are incorrectly calculated if the setting is for a type CAT 3 cable (the
cable insulation containing PVC), but the test is actually performed on a CAT 5 cable
(insulation containing Teflon  ). Therefore, ensure that the correct cable type is selected.
Fig. 82 Impedance Test
6.13.1 Impedance Error
Impedance errors cause signal reflections and signal reduction. Average impedance of wire
pairs should comply with LAN system impedance of 100, 120 or 150
Ω .