RF Loopback Test:
PTP 820/850 series radios have an option for RF Loopback test where the radio itself transmit and receive which can be used to determine the status of Radio Transmitter and Receiver.
In case the RF link parameters (Signal level, MSE, MRMC) are bad or if there are lot of defective blocks and we have verified the physical installation, alignment, but still unable to figure out the cause of issue then we can run RF-Loopback test to check the hardware status.
This Article explains the complete procedure to run RF Loopback test and Interference test**.**
Select Radio > Diagnostics > Loopback. The Radio Loopbacks page opens.
Select the Radio that you want to test and click Edit
To activate a RF loopback, select ON and the Loopback timeout (minutes) to restore traffic (0 = no timeout) > Apply.
Refer below screenshot:
Refer below screenshot to understand what happens during the RF-Loopback test:
Below are the challenges that you may face while running RF Loopback test:
Traffic affecting – RX is stopped, should have maintenance window to perform.
Local access to the Radio would be required running RF Loopback test on both ends.
You cannot perform loopback directly on a multi-Carrier ABC group.
Radio-level diagnostics can be performed on individual members of the group (MC-ABC)
The RF loopback test may not work in case of XPIC setup. For this we must disable XPIC first and then run loopback test.
Below Radio parameters must be configured as mentioned to run proper RF-Loopback test:
For loopback it is recommended to run around 30 min, in that way at least one complete performance cycle of 15 min will show results (for analysis purposes).
To perform radio loopback, the radio must be set to its maximum TX power. Path: Radio>Radio parameters.
When performing RF loopback, the antenna port of the radio must be terminated.
Do not change the TX or RX frequencies while radio loopback is active. Doing so will prevent the radio link from being re-established after the loopback has finished.
The Radio end radio and the second radio core on local radio (If applicable) must be muted (should not be transmitting).
ATPC(Radio>ATPC) and Adaptive Transmit power admin (Radio>Radio parameters> Adaptive Transmit power admin > must be disabled.
The Modulation mode should be fixed with lowest MRMC profile (Profile-0).
After starting the loopback clear the counters, monitor for no defective blocks in the counters during the time of the loopback
RF-Loopback Test Results:
We can see RF Loopback test results under the Radio Parameters.
If RSL, MSE and Defective Blocks are looking good, this transducer and the whole way to it, are operational.
RF loopback acts as if the Rx would be on the same Frequency as your Tx, for the activation period.
RSL value: RSL value is dependent on the Tx Power and any changes performed in Tx Power should be observed in received signal level (i.e., Decreasing 5dB Tx should also reduce RSL by 5dB)
RSL value read on loopback depends on the product, but expect to receive RSL=Tx Power - 60dB (with a margin of ±10dB)
No Defective Blocks should observe (make sure counters are clear before starting loopback, if needed reset counters.)
This test would help us to determine if there is any Interference in the link resulting in low link performance.
Below is the procedure for running Interference test:
Turn off the Remote Radio or TX mute the remote radio, also if applicable mute the second radio core of the local radio as well and check for the RX level at local radio.
Similarly, turn off the local radio or TX mute the local radio and check for the RX level at remote radio.
Results of Interference test:
- In case there is no interference in the link, the Signal level when the other end radio is not transmitting should be around -88 to -99 dBm.
- If the signal level is stronger than -85dBm then this indicates that there is an interference as the unit is receiving some signal from a different site.
- We may have to check for the interferer nearby.
- To avoid or eliminate the impact of interference we can check for the operating frequency and channel bandwidth of the interferer and revise the frequency planning for both the devices such that they do not interfere with each other.