Cable test question

[RebusCom]

For my own edification, on a cable test to a Fast Eth radio, if the results are Okay, Okay, Short, Short, as normal for Fast E, but pairs 3 and 4 show as precisely half the line length of pairs 1 and 2, what would be your best guess as to cause, e.g. near end crimp, far end crimp, cable damage, or any of the above?

[sirhc]

For my own edification, on a cable test to a Fast Eth radio, if the results are Okay, Okay, Short, Short, as normal for Fast E, but pairs 3 and 4 show as precisely half the line length of pairs 1 and 2, what would be your best guess as to cause, e.g. near end crimp, far end crimp, cable damage, or any of the above?

Run the test once powered up.
So long as the cable diagnostics does not detect "cross-short" it is safe to power up with the "correct" POE option.

Cable diagnostics can be affected by a device that is not powered up, this depends on how the manufacturer designed their equipment.

Personally I feel UBNT designed the airFIBER 24 and airFIBER 5 correctly and if you run a cable diagnostics on it when un-powered you will see OPEN, OPEN, OPEN, OPEN. Once the unit is powered up you will see OK, OK, OK, OK.

If you look at the old 10/100 airMAX radios you will see either OPEN, OPEN, SHORT, SHORT or OK, OK,SHORT, SHORT. In my "personal opinion" the POE Ethernet circuits were not designed correctly but rather to save money.

I was upset to see that the new aiFIBER X radios test out as SHORT,SHORT,SHORT,SHORT when un-powered. I was really hoping they would follow the design they used on the original airFIBER 24 & 5.

However if pair lengths show different on a powered ON device and there is not an Ethernet Surge protector in the loop as they can affect this test then the cable was probably damaged during installation where it was either stretched or kinked which damages the cable electrical characteristics such as cross talk and or attenuation between pairs.

what would be your best guess as to cause, e.g. near end crimp, far end crimp, cable damage, or any of the above?

YES!

[RebusCom]

Thanks. The scenario above is when powered up (Rocket N). It seems to be working okay but the problem is indicated.

[sirhc]

Thanks. The scenario above is when powered up (Rocket N). It seems to be working okay but the problem is indicated.

If it is a short jumper cable on my bench (3- 12 feet) I sometimes see that but not on my longer production cable runs unless they are damaged.

CLICK IMAGE TO VIEW FULL SIZE

avatar.jpg (204.76 KiB) Viewed 6032 times