Testing with Loopback IF & DIG (Apex)

The diagnostic tool loopback can be used to check the proper operation of an Apex up to the point where the signal leaves the radio. This can be useful for determining if one side or another may have a hardware issue.

Setting a loopback mode other than off activates one of the loopback modes for test purposes.  This must be turned off by a command when done with testing.  The CLI is still active while the mode is on to allow monitoring of various parameters.  

During IF and digital loopback, the transmitter signal from the far end will still be present at the input to the Apex and may cause a poor result.   Therefore, the opmode OFF on the remote end of may be required to eliminate any signal from the far end which may corrupt the result.

Caution: All loopback modes will stop live traffic from passing across the link and will cause data traffic to loop back out the data port. It is important for this reason that data ports be disconnected or disabled prior to activating loopback.

To use the loopback function to diagnose a particular unit:

1. Establish out of band management access to the unit.
2. Disable or disconnect the data ports. If you're using in band management (IBM) you will also be disabling your management access, so you must establish out of band access.
3. Ensure that opmode is on: opmode on.
4. Activate loopback if.
5. Run the linktest command, possibly with multiple iterations like linktest 10.
6. Check that the lock status is 1 (locked) and record the MSE. The MSE should be -36 or better, typically -36 to -40. If the loopback IF result is in the -36 to -40 range, you can skip the loopback dig testing.
7. Set opmode off.
8. Activate the digital loopback mode by using the command loopback dig. This causes the signal to be looped in the Apex before it goes to the IF stage.
9. Run the linktest command, possibly with multiple iterations like linktest 10.
10. Check that the lock status is 1 (locked) and record the MSE. The MSE should be -40 or better, typically -42. 
11. Set loopback off.
12. If desired turn the transmitter on again, opmode on.
13. Enable or reconnect the Ethernet data ports as needed.