Multiple ePMP 1000 on site self interference issue


      Sorry for bodering you with this kind of situation but since i want to expand my number of Cambium APs from one of my sites i need to know how can i address self interference issue that suddenly appeared.

       In the beginning i had just one ePMP 1000 ap on site, but now the increased number of clients and their subscriptions forced me to add 2 more ePMP 1000 aps looking in the same direction.

      For this situation i took different frequencies with at least 100 Mhz guard but immediately after this setup was in place i started to see major degradation on the uplink speed on the first AP as well on the newest ones. I have checked the performance on the SMs and i saw that the retransmission procent is almost as 20% on uplink  which lead to a speed of 4 Mbps in the best case scenario. Reading on the community i understood that self interferences came in place and need to lower them.

   So for this moment the best next thing i thought is to enable GPS sync, thinking that if all APs will talk and listen in the same time all the self interferences will go away. That being said i started to configure the GPS sync paramenters on radio menu such as :

- Distance = 15 KM

- Frame Ratio = 75/25

- Sync source = GPS

- channel width = 20Mhz

        Please tell me if there are any other parameters that need to be corellated such as maximum number of subscribers or co-located option on top of sync source in order to have full sync between all of my APs, this is crucial i think in order to maintain a good uplink speed to all my existing and future clients.

        My subscriptions are : up to 5 mbps up / 20 mbps down and 10 mbps up / 50 mbps down and the total number of clients on one APs is intended to be as  high as 55 or 60.

       Further more please tell me how come i can accomodate a force 110 link in this tower even if it's at 300 Mhz apart from APs chunk of frequencies. I want to use this link in eptp mode for low latency reasons, but if this cannot be achieved i will move this link in another frequency (11/18 ghz ).

Thanks in advance for your answers,


Can you post what sector antennas you are using and what freqs?

Also can you tell us how far apart they are (physically)?

What freq is your backhaul in?


for this setup i'm using :

old ap : 5780 mhz
ap2 covering the same area as the old ap : 5650 mhz
ap3 covering 90 degree apart from those first 2 : 5840 mhz
PTP link using Force 110 and ePTP mode paralel with ap3 but steered a little bit to the right : 5525 Mhz

For old ap,ap2 and ap3 we are using 90 degree sector antena from cambium. The distance between all of them is maximum 3 meters. for those covering the same area the antenas are one beneath the other having 10 or 20 cm separation.

The Force100 link in Eptp mode is not syncronized, so consider it a source of interference, and make sure to use the lowest possible TX/RX-power.

What value is set in the "GPS holdoff timer" at these AP's?  
How many sattelites are tracked by each AP? check the Syslogs to see if one of them is loosing Sync.

Do you have any synced sectors in other towers arround doing frequency reuse?; 
What frequency reuse option is selected? (None || Front || Back)?

Is you farthest client really 15km away?  you could (if you don't have other sectors synced arround), try to lower that value , say, if all your customers are in a 3km radius. 

Can you post a screenshot of the "Monitor>>Wireless>>Show List" tab for these AP's?
Just cut the MAC/Ip/Device names in paint.

snyc will help a lot here.  this looks like a case of co-band noise, GPS sync does 2 things, allows for frequceny reuse, and deals with co-band noise.  

if you can, make sure your PTP radio is decent distance away from your multipoint.    it won't be snyced with your multipoint and distance plus good atennas will stop the co-band noise for that device.     also if you've got a specific area needing more access aside from the 90 degree area,  RFelements twist ports are a good solution. they have great SNR numbers and made for a tiny area.

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                Thank you all for your answers, currently i don't have the option to use another backhaul frequency apart from 5,4 - 5,8 Ghz.

                 My question for you all is that if i could separate PMP modems at lets say 200 Mhz apart from my 3 x PTP links the co-band interference will be at the same level.

These 3 PTP links are using 40 Mhz and PMP which are 4 on the same tower use 20 Mhz channels.

                 All PMP devices are synced using the following configuration :

                                    - Max Distance : 15 Km

                                    - 20 Mhz wide channel

                                    - 75/25 ratio

                                    - 2.5 ms frame size

                  PTP links are at different distances with different throughput using :

                                    - 1 x Mikrotik NetMetal 5 Ghz AC pair (5km , 250 Mbps down / 80 Mbps Upload)

                                                           (here maybe i can think using a PTP650 link if the effect over co-band noise will worth)

                                    - 1 x epmp 1000 + 25 DB directional antena pair using ePTP mode (13 km, 90 Mbps up / 90 Mbps down)

                                    - 1 x Force 180 pair using ePTP mode (0.5 km, 100 Mbps down / 100 Mbps up ) - new temp link, planning to be swapped with epmp 1000. 

Thank you all for support and maybe if you visit romania we can meet live ;) !

Best Regards,


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