3.65GHz 450 LBT issue

We have a 3.65GHz 450 AP with a 90 degree sector on one of our mountains, and we are the only operator registered in 3.65GHz for that mountain.  Since we installed the new AP, we have had nothing but troubles with LBT events.  We have tried changing channels, narrowing the channel, reducing the "Transmit Output Power",  turning on adjacent channel support, and upgrading/downgrading firmware between 13.1.3 and 13.3 to no avail.  We have done numerous spectrum annalysis, and none of them come back with noise levels that would trigger a LBT event, yet the logs show three to four hits a day at very high signals.  I have attached a spec ann and posted the LBT logs.  

There is a Ubquiti 3.65GHz pointed in the opposite direction, which is what is seen in the attached spectrum annalysis in the lower 3.65GHz frequencies.  Oddly, the Cambium 3.65 seems to run worse at 3695 than it does at 3685.

Has anyone else had this issue or have any suggestions?

Thanks,

Mike S.

06/11/2015 : 15:41:51 PST : Normal Transmit for 3685.00 MHz
06/13/2015 : 15:33:26 PST : Transmit Off, interference detected for 3685.00 MHz, -76 A / -64 B dBm
06/13/2015 : 15:33:29 PST : Normal Transmit for 3690.00 MHz
06/13/2015 : 15:39:00 PST : Transmit Off, interference detected for 3690.00 MHz, -62 A / -52 B dBm
06/13/2015 : 15:39:03 PST : Normal Transmit for 3695.00 MHz
06/13/2015 : 18:21:46 PST : Transmit Off, interference detected for 3695.00 MHz, -64 A / -59 B dBm
06/13/2015 : 18:21:49 PST : Normal Transmit for 3685.00 MHz
06/14/2015 : 17:38:49 PST : Transmit Off, interference detected for 3685.00 MHz, -61 A / -55 B dBm
06/14/2015 : 17:38:52 PST : Normal Transmit for 3690.00 MHz
06/14/2015 : 19:56:55 PST : Transmit Off, interference detected for 3690.00 MHz, -63 A / -58 B dBm
06/14/2015 : 19:56:58 PST : Normal Transmit for 3695.00 MHz
06/15/2015 : 07:28:08 PST : Transmit Off, interference detected for 3695.00 MHz, -63 A / -53 B dBm
06/15/2015 : 07:28:10 PST : Normal Transmit for 3685.00 MHz
06/15/2015 : 10:55:06 PST : Transmit Off, interference detected for 3685.00 MHz, -64 A / -54 B dBm
06/15/2015 : 10:55:08 PST : Normal Transmit for 3690.00 MHz
06/15/2015 : 11:19:45 PST : Transmit Off, interference detected for 3690.00 MHz, -61 A / -52 B dBm
06/15/2015 : 11:19:48 PST : Normal Transmit for 3695.00 MHz
06/15/2015 : 15:42:49 PST : Transmit Off, interference detected for 3695.00 MHz, -75 A / -63 B dBm
06/15/2015 : 15:42:51 PST : Normal Transmit for 3685.00 MHz
06/16/2015 : 11:22:36 PST : Transmit Off, interference detected for 3685.00 MHz, -63 A / -54 B dBm
06/16/2015 : 11:22:38 PST : Normal Transmit for 3690.00 MHz
06/16/2015 : 12:27:23 PST : Transmit Off, interference detected for 3690.00 MHz, -63 A / -56 B dBm
06/16/2015 : 12:27:25 PST : Normal Transmit for 3695.00 MHz
06/16/2015 : 17:25:31 PST : Transmit Off, interference detected for 3695.00 MHz, -74 A / -63 B dBm
06/16/2015 : 17:25:34 PST : Normal Transmit for 3685.00 MHz
06/16/2015 : 18:38:39 PST : Transmit Off, interference detected for 3685.00 MHz, -67 A / -53 B dBm
06/16/2015 : 18:38:42 PST : Normal Transmit for 3690.00 MHz
06/16/2015 : 21:14:18 PST : Transmit Off, interference detected for 3690.00 MHz, -66 A / -54 B dBm
06/16/2015 : 21:14:21 PST : Normal Transmit for 3695.00 MHz
06/16/2015 : 21:37:15 PST : Transmit Off, interference detected for 3695.00 MHz, -63 A / -61 B dBm
06/16/2015 : 21:37:18 PST : Normal Transmit for 3685.00 MHz

Hi, I am guessing that what you are likely facing is spurs (Spurious emissions) from the Ubiquiti radio, especially when it is set to transmit at max power. We've had one other customer under the same situation. Luckily he owned the Ubiquiti AP as well, so he was able to turn it off and verify it was the problem. A Spectrum scan will not capture spurs as they are instantaneous spikes and you will need a high performance VSA to catpure it. However, the 450 reciever is able to detect it and trigger an LBT event. Perhpas you can try downtiling your sector to help the situation at the cost of reduced range? But if the interference is too high, then this will not help. 

Thanks,

Sriram

If it's the ubiquiti that is causing the trouble, I am tempted to try shielding kits on the radios.  I know i can get one for ubiquiti, but is there one available for Cambium?

Is it also possible that the 13.4 firmware may also help the issue?

It would really be unfortunate if the two AP's can not be co-located on the same tower.  We have a good number of clients on the ubiquiti and limited alternatives in the direction it faces.

Thanks again for your help and quick response

-Mike S.

Hi, shielding on the Ubiquiti may help. Remember that these are spurs from the Ubiquiti so shielding the Cambium radio is unnecessary and will not help.

OK, we haven't yet installed the shield kit yet, but we have turned down the ubiquiti a couple of decibles and upgraded the Cambium 3.65 450 to firmware 13.4.   After the firmware update, we noticed that the LBT is being triggered on frequencies listed below.  This puts the trigger events 3GHz below our center frequency.  Any ideas?

07/23/2015 : 23:18:29 MST : Normal Transmit for 3685.000 MHz
07/24/2015 : 18:58:37 MST : Transmit Off, interference detected for 408.200 MHz, -76 A / -64 B dBm
07/24/2015 : 18:58:40 MST : Normal Transmit for 3690.000 MHz
07/24/2015 : 19:52:42 MST : Transmit Off, interference detected for 413.200 MHz, -77 A / -64 B dBm
07/24/2015 : 19:52:45 MST : Normal Transmit for 3660.000 MHz
07/26/2015 : 08:15:30 MST : Transmit Off, interference detected for 383.200 MHz, -65 A / -64 B dBm
07/26/2015 : 08:15:33 MST : Normal Transmit for 3685.000 MHz
07/27/2015 : 16:37:58 MST : Transmit Off, interference detected for 408.200 MHz, -78 A / -64 B dBm
07/27/2015 : 16:38:01 MST : Normal Transmit for 3690.000 MHz
07/27/2015 : 16:38:24 MST : Transmit Off, interference detected for 413.200 MHz, -89 A / -64 B dBm
07/27/2015 : 16:38:27 MST : Normal Transmit for 3660.000 MHz
07/27/2015 : 20:22:23 MST : Transmit Off, interference detected for 383.200 MHz, -67 A / -64 B dBm
07/27/2015 : 20:22:25 MST : Normal Transmit for 3685.000 MHz
07/28/2015 : 17:31:56 MST : Transmit Off, interference detected for 408.200 MHz, -88 A / -64 B dBm
07/28/2015 : 17:31:59 MST : Normal Transmit for 3690.000 MHz
07/28/2015 : 18:08:32 MST : Transmit Off, interference detected for 413.200 MHz, -80 A / -64 B dBm
07/28/2015 : 18:08:35 MST : Normal Transmit for 3660.000 MHz
07/28/2015 : 23:18:40 MST : Transmit Off, interference detected for 383.200 MHz, -65 A / -65 B dBm
07/28/2015 : 23:18:43 MST : Normal Transmit for 3685.000 MHz

1 Like

Haven't seen a response to this in three weeks, but here is an update on this side of things.  We have added a shield kit to the Ubiquiti 3.65, turned down the Ubiquiti 3.65 power levels, adjusted channels on the Cambium 3.65, adjusted channel width on the Cambium 3.65, downgraded/upgraded firmware on the Cambium 3.65.  We continue to have LBT events no matter what we have tried, and we have two other Cambium 3.65 AP's on different locations that have no trouble at all.

Additionally when the channel width on the Cambium 3.65 is 10 wide, the problem strikes more often when we at 3.690GHz than it does when we are closer to the Ubiquiti.  We have even gone so far as to put both AP's on the same channel, and we see fewer LBT events than at 3.690GHz.  The fact that the logs show interferance in the 400MHz range is concerning.  This particular AP is located on a public tv broadcast tower.  Is it possible that the interferance is coming from them?  Or is it possible we have a bad access point?  If you notice the logs, the interferance is almost always on chain B which seems a bit unusual. Additionally, the installtion of the shield kit to the Ubiquiti and adjustment of the TX power has not affected the frequency of LBT events or the levels of interferance.

08/18/2015 : 08:23:00 MST : Transmit Off, interference detected for 413.200 MHz, -67 A / -64 B dBm
08/18/2015 : 08:23:03 MST : Normal Transmit for 3680.000 MHz
08/18/2015 : 09:04:15 MST : Transmit Off, interference detected for 403.200 MHz, -67 A / -64 B dBm
08/18/2015 : 09:04:17 MST : Normal Transmit for 3685.000 MHz
08/18/2015 : 11:31:08 MST : Transmit Off, interference detected for 408.200 MHz, -70 A / -64 B dBm
08/18/2015 : 11:31:10 MST : Normal Transmit for 3690.000 MHz
08/18/2015 : 14:13:13 MST : Transmit Off, interference detected for 413.200 MHz, -68 A / -64 B dBm
08/18/2015 : 14:13:15 MST : Normal Transmit for 3680.000 MHz
08/18/2015 : 14:16:35 MST : Transmit Off, interference detected for 403.200 MHz, -68 A / -64 B dBm
08/18/2015 : 14:16:38 MST : Normal Transmit for 3685.000 MHz
08/18/2015 : 14:46:33 MST : Transmit Off, interference detected for 408.200 MHz, -67 A / -64 B dBm
08/18/2015 : 14:46:36 MST : Normal Transmit for 3690.000 MHz
08/18/2015 : 14:48:22 MST : Transmit Off, interference detected for 413.200 MHz, -69 A / -64 B dBm
08/18/2015 : 14:48:24 MST : Normal Transmit for 3680.000 MHz
08/18/2015 : 15:09:05 MST : Transmit Off, interference detected for 403.200 MHz, -67 A / -64 B dBm
08/18/2015 : 15:09:08 MST : Normal Transmit for 3685.000 MHz
08/18/2015 : 18:05:22 MST : Transmit Off, interference detected for 408.200 MHz, -66 A / -64 B dBm
08/18/2015 : 18:05:25 MST : Normal Transmit for 3690.000 MHz
08/18/2015 : 19:36:45 MST : Transmit Off, interference detected for 413.200 MHz, -66 A / -64 B dBm
08/18/2015 : 19:36:47 MST : Normal Transmit for 3680.000 MHz
08/18/2015 : 20:36:57 MST : Transmit Off, interference detected for 403.200 MHz, -66 A / -64 B dBm
08/18/2015 : 20:37:00 MST : Normal Transmit for 3685.000 MHz
08/18/2015 : 21:22:23 MST : Transmit Off, interference detected for 408.200 MHz, -66 A / -64 B dBm
08/18/2015 : 21:22:26 MST : Normal Transmit for 3690.000 MHz
08/19/2015 : 06:25:15 MST : Transmit Off, interference detected for 413.200 MHz, -71 A / -64 B dBm
08/19/2015 : 06:25:17 MST : Normal Transmit for 3680.000 MHz
08/19/2015 : 06:35:26 MST : Transmit Off, interference detected for 403.200 MHz, -68 A / -64 B dBm
08/19/2015 : 06:35:29 MST : Normal Transmit for 3685.000 MHz
08/19/2015 : 07:09:06 MST : Transmit Off, interference detected for 408.200 MHz, -70 A / -64 B dBm
08/19/2015 : 07:09:09 MST : Normal Transmit for 3690.000 MHz
08/19/2015 : 08:09:21 MST : Transmit Off, interference detected for 413.200 MHz, -71 A / -64 B dBm
08/19/2015 : 08:09:24 MST : Normal Transmit for 3680.000 MHz
08/19/2015 : 08:34:15 MST : Transmit Off, interference detected for 403.200 MHz, -69 A / -64 B dBm
08/19/2015 : 08:34:17 MST : Normal Transmit for 3685.000 MHz

Hi,
The logs stating 413.200 MHz is wrong, sorry about that.
They should actually be saying 3680.000 MHz.

We have this 400 MHz print issue fixed in 13.4.1 and the beta is expected to be available next week. 

We've had the exact same problem for months.  It always happens on the B channel as well. There are no other operators anywhere nearby, as none are registered and doing a spectrum scan with all other APs off one night verified this.  We don't have anything pointing in another direction either.  I finally just lowered the transmit power by 3db and this increased the LBT threshold enough where the problem stopped happening.  Not an ideal fix, but a weaker signal is better than no signal for now!

1 Like

Thank you for your response.  We have also tried this, and you are correct that it helps reduce the number of LBT events.  We have also found that adjusting the channel width to 10 wide seems to help, but doesnt completely resolve the issue.  At this point, where we haven't been able to come to a solution that will allow us to install clients with sensitive connections to this AP; my company has decided to remove the Cambium 3.65 from the tower and replace it with something else.

I am hoping to try it again in a different location, as I have a feeling it is a bad AP.

We have been experiencing these LBT hits on one of our AP's in a 4 cluster setup for about two months now.  It just started happening out of the blue.  Is the general consensus here that turning down transmit power corrects this issue?  I must be 200 miles from the nearest Radar station and this is just becoming unacceptable for this product.  We have a competitior running Ubiquiti 3.65 that would be facing this AP and even though those M3 radios will only transmit in lower 25Mhz (and we are transmitting in upper 25mhz of that band) I suspect this is the issue.  I don't think I can decrease our transmit 3db and it have an impact on our longer links.  Any suggestions?

Couple questions... and things to try:

  • Are you using the Cambium antenna part number C030045D901A, or not, what 3rd party antenna(s) are you using? If using 3rd party, make sure that they have at least as good, if not better F/B ratio as Cambium antenna.
  • What kind of physical seperation and/or shielding is between you and the UBNT 3.65 radios? Put as much space as possible between your PMP450 radios and the UBNT radios.
  • Are the UBNT 3.65 radios and antennas using RF Armor shield kits? If no, then they should be.
  • For PMP450 sectors that are physically close to or are directly facing UBNT sectors, make sure that both radio's channels are as far apart as possible... e.g. UBNT @ 3655 and PMP450 @ 3695.
  • If you're using back to back frequency reuse AND you're not using any spacing between adjacent channels, make sure you enable 'adjacent channel support' on all AP's in the cluster.
  • On all AP's set SM recieve target level to -68dBm or less. Do not set to -65dBm or stronger.
  • Upgrade all AP's and SM's to 13.4 if you haven't done so already.
  • Make sure all AP's are getting proper GPS sync timing, check log  for GPS sync issues.
2 Likes

Eric,

Thanks for your suggestions.

Yes, we are using Cambium 90 degree sectors. 

I cannot say for sure about the Ubiquiti radios because they are not ours and they are located across town but I'm certain that their North AP is facing our South AP, for example.  We only use the upper 25Mhz of the 3.65 band because it's cleaner due to Ubiquiti's inability to transmit in the upper 25Mhz.  I have 3.5 or more guard band between our two 10Mhz channels and the AP in question is transmitting at 3695 (which should be the furthest away from what a Ubiquiti M3 Rocket could even transmitt. The nearest TDWR site is probably 400 miles away from the direction of this AP.  

I have flashed everything to 13.4 which did help reduce LBT but still not 100%.  We service several businesses off this AP so I'm about ready to pull my hair out.  

In regards to target recieve, we have found that this makes no difference for us.  I have set the target recieve above and below the LBT Thresholds and also went ahead and added additional artificial external gain to really close SM's to turn their power down manually.  In fact, when I was playing with this for about a week, it had more LBT hits when power in SM's was turned down to combination of target recieve and adding artificial external gain and not less. 

The bottom line is this is not actually radar being detected and I'm getting pretty frustrated.  Do you think Cambium support can manually adjust the sensitivity to LBT?  I'm checking GPS logs and will report back if I find anything out of sorts.  

Thanks for your response.  Appreciated.

Nathan

This is more of a band-aid than a fix (until someone at Cambium can check your AP(s) out)...

  • Try 10, 7 and 5MHz channel modes and see if you have better LBT luck. It might not be an ideal bandwidth situation, but it would be interesting to see if you still see LBT events. IIRC the LBT threshold is better for smaller channel widths.
  • Do not use secondary/tertiary backup channels on your AP. If the AP experiences an LBT event, it will just keep trying the same channel over and over again immediatly.
  • Remove all other checked channels and channel widths other then the one you're trying to operate on on your SM's, which should cause them to associate almost immediatly in the event of an LBT hiccup.

Again, not a fix, but it might significantly reduce the downtime your business customers are experencing from a minute outage to a brief couple second hiccup that they will probably not even notice.

Do these things first, and then in the mean time open up a support ticket with Cambium and have them look over your AP and see what can be done.