820s 2+0 Signal Horrible - Installation Mess Up or Defective Radio?

[nivlage999]

Hey everyone, I am scratching my head over here.   This is our first licensed link deployment and we're having some issues.

We installed a 13 mile, 6ghz link made up of two 820s 2+0's with 3' radiowave dishes  and the PCN shows the signal should be -39, but the best we can get is -68 after re-aligning both sides multiple times. 

Today on one side I took the ODU's off of the OTC(combiner) and checked to make sure the waveguide(little disc) on the ODU was set properly.  One of the ODU's has the v set in the 12 oclock noon position and the other ODU has the h set to the 12 o clock position.  I am guessing this is how it should be with the 2+0 configuration as well.

We also changed the circular mount on the back of the radiowave dish in order for the OTC to fit on there properly - it all came with the cambium link planner kit.  

The instructions refer to rotating the OTC on the back of the dish to get maximum cross polarization difference.  We tried rotating the OTC with the two ODU's on it left, right, center and all variations in between on both sides and yes the signal changes, but not for the better on both sides at the same time.

We really don't know what to do.  We have the vertical ODU set to vertical on the combiner, same with the horizontal, but this just doesn't make sense.  

Does anyone have any experience with the 2+0 set up and maybe you can help me out a little?  We have 2 links and can't finish the first yet - we haven't started on the second and don't want to until we figure out the solution to this first pair. 

I have attached random pics outlining our setup.  

[RayS]

I have forwarded this to our support team. Please also contact them at support@cambiumnetworks.com.

[nivlage999]

Thanks, I have a ticket open as well. Appreciate it!

[RayS]

I saw the other post about how it may be a polarity mismatch. did you check for that?

[allenyu (Allen Yu (inactive))]

here is few suggestions and recommendation for installation of PTP820S 2+0 configuration. If your antennna alignment is done properly, the issue probably on the twist alignment on the radio. As a wrong twist could add 30 dB loss.

Things to check:

1. Adjust the twist of PTP820S, make sure each radio has correct V and H polarity. You shall find following details in PTP820S installation manual.

2. The OMT has one port as  Vertical and one port as Horizontal. You need make sure Radio has Horizontal polarity match with OMT Horizontal port, the radio has Vertical polarity match with OMT Vertical port.

3. Attach the OMT with antenna, use a level to make sure OMT is leveled. No need to twist the OMT if both side is levelled.

4. Enabled one of the radio ONLY and align the antenna. If antenna alignment is done properly, you shall see the receive  level match the guidance provided by linkplanner.

5. Once finished, turn on both radio. You work shall be done.

Regards

Allen

[nivlage999]

See my responses inline.  

1. Adjust the twist of PTP820S, make sure each radio has correct V and H polarity. You shall find following details in PTP820S installation manual.  -

*****We have checked one side and tomorrow we will be going up and checking the other end.  All looks good on the first side.  

2. The OMT has one port as  Vertical and one port as Horizontal. You need make sure Radio has Horizontal polarity match with OMT Horizontal port, the radio has Vertical polarity match with OMT Vertical port.

******This has been triple checked in the lab before deployment, but we are going up again tomorrow to verify the side that has not been checked again since we deployed. 

3. Attach the OMT with antenna, use a level to make sure OMT is leveled. No need to twist the OMT if both side is levelled.

**** Ok.  Thanks.  I am glad to hear that it is just to make sure the omt is leveled.  Thanks. 

4. Enabled one of the radio ONLY and align the antenna. If antenna alignment is done properly, you shall see the receive  level match the guidance provided by linkplanner.

***Ok.  Link planner says we should be at -39.  We can try muting one radio on both sides.  Worst case scenario we will have to put them on with one polarity only and see if the problem still exists.  

5. Once finished, turn on both radio. You work shall be done.

*****One thought I have had is that I dont think it is a polarity mismatch because for that to be true, one of the radios should be within a great signal range.  All of the 4 RX signals are between -62 and -67.  

For us to see this issue, it seems that there would have to be a mismatch on at least one radio from both sides.  One side has been taken apart and inspected, so unless the other end has errors on both radios, I don't see how the problem will be resolved.  

The most logical consideration is that the ODU's were put on the wrong side of the OMT - as in the ODU's were set correctly and then just put on the wrong side.  The reason I doubt that is because I had my employee take them all apart one more time before deployment, but it's possible he made a mistake.  

If just one of the two odus were set incorrectly, that would mean that one is set correctly - and that one would connect to the other end which has been verified.  

Hope I did a good job explaining this.  

[nivlage999]

Hey Allen,

Today 8 have received 100% confirmation, with video documentation from both sides that everything is installed 100% to your specifications and the issue still exists.

All was installed properly the first time.

I can upload videos and pics when I have some time this Friday after the Wispa show, but believe me when I say that I have confirmation all is correct.

What do we do now?

[David_Hensley]

This appears to be a 2+0 cross-polar link. (It's not an XPIC link.)

It's possible that the V on one end is using the frequency pair to talk to the H on the other end.

Have you checked that?

Mute the H radios.

Check the RF status of the V link. Is the power still about 30 dB too weak, even though the link is aligned and the OMTs are level? At one end, mute the V radio and unmute the H radio. Configure this H radio with the V frequencies. Does the power improve by 30 dB or so? If yes, you appear to have swapped the V and H at one end.

To summarize, the near end V needs to be aligned with the far end V, and the V radios need to use the same Tx/Rx frequency pair. (One end uses Hi/Lo, and the other end uses Lo/Hi, but they should use the same pair.)

The near end H needs to be aligned with the far end H, and the H radios need to use the same Tx/Rx frequency pair. (Again, one end uses Hi/Lo, and the other end uses Lo/Hi.)

In addition to all of this, both Hi's have to be at the same end, and both Lo's have to be at the same end.

I hope this helps!

Dave

[nivlage999]

All that you have mentioned has been triple checked.

Are we sure there isn’t another piece for the cross polar links in 6ghz that goes between the odu and OMT?

[nivlage999]

So luckily we found out that 2 of the ODU's were swapped regarding their programmed frequency - so the v was connected to the h on both radios.  We swapped it and all is back and running great at  -44 & -41.16 MSE

[RayS]

Great. I am glad that all is good. Can you send us some photos when these are up and running?