First, let's understand the concept of ANEXT. What is ANEXT?
ANEXT is short for Alien Near-end Crosstalk loss, also known as external near-end crosstalk loss. ANEXT contains near-end crosstalk attenuation
between the primary and the keyed pairs in different cables.
So why we test ANEXT?
Figure 1: Data center machine room bundle laying
Figure 2: Security monitoring bundle laying
At present, many application scenarios of cabling are bundle laying, such as data center room, security monitoring engineering, intelligent
building projects, etc., then it is necessary to consider the level of cable
resistance to external crosstalk. Therefore, an external proximal crosstalk attenuation test was used to measure.
Let's look at how ANEXT tests work.
Figure 3 Interference between cable groups
ANEXT test adopts the "6+1" test mode. The test principle is that the peripheral 6 cables are used as the main cable and the main cable is carried out around the center 1 cable. The main cable and the cable
located in the center are tested successively, and the total number of tests is 96 (4x4x6).
In practical applications, because the same manufacturer or even the same batch of cables are usually used in the wiring process, the core
geometry of the same color (core to wire) is almost the same, so the
interference between the core of the same color is particularly serious. (Refer to resonance phenomena in physics).
Figure 4 Interference between cores of the same color
The external proximal crosstalk attenuation test items are
represented by the external proximal crosstalk attenuation power and PS ANEXT and calculated by the following formula.
PSAX-talkj- The sum of the external crosstalk power of the line to j, expressed in dB
AX-talki,j,l - Specifies the crosstalk attenuation, in dB, between the line pair j of the cable and the line pair i of the adjacent cable
j- The number of the string pair i-Number of the main string pair
l- Serial number of the main cable
n- Total number of primary string pairs N- Total number of main series cables
External proximal crosstalk attenuation power and (PS ANEXT) | ||
Lan cable | frequency(MHz) | Proximal crosstalk attenuation power and (PS ANEXT), minimum (dB) |
6A | 1-500 | PS ANEXT≥92.5-151g(f) |
7A | 1-1000 | PS ANEXT≥107.5-151g(f) |
frequency(MHz) | External proximal crosstalk attenuation power and (PS ANEXT), minimum (dB) | |
6A | 7A | |
1.00 | 67.00 | 67.00 |
4.00 | 67.00 | 67.00 |
8.00 | 67.00 | 67.00 |
10.00 | 67.00 | 67.00 |
16.00 | 67.00 | 67.00 |
20.00 | 67.00 | 67.00 |
25.00 | 67.00 | 67.00 |
31.25 | 67.00 | 67.00 |
62.50 | 65.60 | 67.00 |
100.00 | 62.50 | 67.00 |
200.00 | 58.00 | 67.00 |
250.00 | 56.50 | 67.00 |
300.00 | 55.30 | 67.00 |
400.00 | 53.50 | 67.00 |
500.00 | 52.00 | 67.00 |
600.00 | / | 65.80 |
1000.00 | / | 62.50 |
If the calculated value is greater than 67dB, set the minimum value to 67dB.
ANEXT test sample strapping
Before the test, 7 samples of 100-meter-long cables to be tested
should be prepared and each cable should be marked in advance. These cables should be made from the same production batch. The 7 cables
should be bundled in straight lines along the entire length to form a "6+1" structure.
Cables should be kept straight and untwisted during bundling. Cables should be evenly bundled with insulation tape or other similar strips at
equal intervals. The bundling strength should be appropriate to ensure that the overall structure of cables is not damaged and the bundling
interval should be 200MM.
Laying mode: circular laying
Figure 5 Test scenario layout of 1+6 bunched cable samples
Cyclic laying is shown in the figure above. The cyclic spacing should be no less than 100mm. The laying site should be non-metallic ground.
Figure6: 6 Around 1 Cable configuration for Alien Crosstalk Test
Figure7: crosstalk test results
As can be seen from the chart, the upper half of the chart shows
proximal crosstalk attenuation, while the lower half of the chart shows distal crosstalk attenuation. Among all the line pairs, only one and two line pairs are coupled, and the crosstalk attenuation between the two
groups is slightly larger than that of other groups. The proximal crosstalk attenuation is 7.55dB, and the performance is also excellent. The other
lines are excellent for both proximal and remote crosstalk performance.
Experimental results: Test network cable samples, near and far end crosstalk attenuation all line pairs PASS, the cross-stalk performance
between groups is excellent.