Here is a rough guide of issues to look for when troubleshooting a PTP820/PTP850 link:
Link not established
- Look at the RSL – if it’s -90dBm then is the transmitter still muted on the other end? Check that the transmitter in radio parameters is set to “unmute”.
- Is tx power set correctly? If it was set to the lowest setting in a lab be sure to turn it up to the allowed transmit power as dictated by your PCN.
- Is it a LOS link or are there obstructions? If it’s NLOS then this will severely degrade the signal and potentially prevent the link from working.
- Has it been aligned properly? During the alignment process be sure to spend sufficient time aligning azimuth and elevation until the RSL is within 5dB of the predicted RSL.
- Are the radio parameters set correctly? Check the tx and rx frequencies and ensure that they are correctly configured and that they match the PCN.
- Is the right sub band used? Ensure the sub bad has a range that supports the assigned frequencies.
- Are they paired Hi/Lo properly? Ensure that the frequency pair has been configured appropriately for the Tx Hi and Tx Lo pair of radios and that the Hi side and Lo side are installed at the correct locations and in compliance with the PCN.
- If RSL is good then look at the MSE – if it’s -99dB check the MRMC scripts and make sure they’re identical.
- If it’s not XPIC ensure that the radios are configured for the correct polarizations. Radio 1 is H-pol and radio 2 is V-pol. If it’s 820S/PTP850S single core make sure both ends are set to the right polarization. If one radio is on the wrong polarization from the remote end this will result in 30dB lower RSL.
- Make sure the dish has the right interface. For 2+0 cross-pol/XPIC if one polarization has achieved the desired signal but the other has not then check to make sure the dish has a circular interface and not the rectangular interface that it ships with. Radiowaves and Commscope have manufacturer specific OMT interfaces to replace the rectangular interface that each dish ships with
- Check that the link ID matches as well.
Link established, but speed is poor
- If RSL is lower than predicted then:
- Check alignment and ensure the link is not on a side lobe. This may take more fine tuning.
- Check the path and verify LOS and that there are no unaccounted obstructions.
- If RSL is good and matches predicted RSL, but MSE is poor (MSE should be -40dB when well aligned):
- It could be interference. Ensure the Tx Hi/Lo radios are installed at the correct locations and not swapped. This could receive and create interference due to being in violation with the frequency coordination.
- If MSE is only poor on one radio in a 2+0 XPIC setup it’s possible that there is a hardware issue. Run a loopback while the remote radio is muted on both cores. A loopback should yield an RSL of about 60dB less than the tx power.
- It could be poor XPI leading to high self-interference. XPI should be 25+ dB, ideally 30+ dB on both cores. This can be fine tuned via the OMT, which has about 5 degrees of flexibility. Also, ATPC is recommended for XPIC links.
Link established, great MSE, but link not passing traffic
- Check to make sure services are setup properly.
RSL degrades/fluctuates over time
- If it degrades over the course of several days and the trend in the PM & Statistics shows that it’s getting worse then it could be wind having blown it out of alignment. Installation may not have been sufficiently robust, if it’s a larger dish like 4’ or larger it may need a stiff arm.
- If it fluctuates and drops but returns to the predicted RSL it is due to temporary environmental conditions like rain, ducting, etc.
RSL is steady, but MSE and modulation fluctuate
- Interference will cause this.
There has been a PTP820 troubleshooting post that you can find here. This has a few additional scenarios to be cognizant of.