Expected ePMP1000 AP behaviour when DFS Status = ISM at Alternate Channel

Hello All,

I have a peculiar issue with an ePMP1000 AP that I hope someone might be able to help with.

It is displaying its DFS Status as "ISM at Alternate Channel" on the System Summary screen.

From the Cambium User guide, the status message is described as "In-Service Monitoring at Alternative Channel: The radio has detected a radar pulse and has moved operation to a frequency configured in DFS Alternative Frequency Carrier 1 or DFS Alternative Frequency Carrier 2."

However the AP has not switched to its 1st or 2nd alternate frequencies that are configured. The operating frequency is still the primary frequency.

The AP has not displayed any RADAR (DFS) detections either in System Statistics (Monitor-->Performance).

The AP has v2.4.1 firmware and the primary frequency has a bandwidth of 40MHz and the alternate frequencies configured have a bandwidth of 20 MHz.

I have raised a case with Cambium technical support and have been advised that the AP could be partially detecting interference and but may not be automatically switching to the alternate frequency because of the fact that the primary channel has a 40 MHz bandwidth and the alternate frequencies have 20MHz bandwidth.

Is this a plausible reason for the behaviour?  It doesn't explain however why the AP has not detected/reported any DFS events?

Also, although detections are classed as RADAR detections, the Cambium support guy stated that the AP will "treat any strong energy received on that channel as RADAR signal".

Is this the case that any interference on the channel is considered a RADAR signal and not just specific RADAR pulses?

This might be a red-herring but one of the SM's connected to the AP has reported DFS detections and has been having intermittent connection issues but none of the other SM's attached to the AP have any issues, including SM's adjacent to the problem SM, none have detected DFS events and all have good signal strengths and SNR's.

Would the AP report a local interference issue for just a single SM in this way?

Appreciate any thoughts and comments on the above.

Best Regards,

Hello Professor K,

First of all I would like to mention that DFS detection behavior depands on Regulatory which complies with   devices locks(ETSI/FCC) and configured Country Codes.

I can guess you have some ETSI Country Code configured.

For FCC locked and ROW devices with Country Code - US, radar can be detected only on AP side. SM does not perform operating channel check for radar detection.

For ETSI locked devices and ROW devices with ETSI Country Code,  radar can be found both on AP and SM side. In case when Radar was detected on AP side - AP moves to Alternate channel and it does not depend 10,20 or 40 MHz BW configured. In case Radar was detected on SMs side - SM stops transmittion and waiting for 30 minutes and then perform operating channel check again.

Only specific pulses are considered as Radar on ePMP devices.

But sometimes very rarely(when interferer behaviour looks like Radar pulses) strong interferer may causes issue when interferer will be considered as Radar.

About the issue you have seen on your device, I would be really appreciate it if you could tell what Country Code is configured on device and is that issue reproducible on 2.4.1 FW and on 2.5.2 FW.

Thank you in advance.


Hi Fedor,

Yes the units are indeed ETSI, specifically United Kingdom as Country Code.

The SM is at 2.4.3 and the AP at 2.4.1.  

I have attached some screenshots that illustrate the issue (sensitive details removed)  

As we have a lot of live subscribers on the AP we have to forward plan and notify any outages and upgrades so I will not be able to test v2.5.2 for some days.

Thankyou for clarifying the radar/inteference detection functionality.

1 Like

Professor K,

I see what is root cause of that issue.

You have configuration:

Frequency Carrier - 5745 MHz (40 MHz Bandwidth)

Alternate Frequency Carrier 2 - 5735 MHz (20 MHz Bandwidth)

40 MHz Bandwidth channel includes two 20 MHz channels.

5745 MHz is a central frequency for 40 MHz BW channel. First 20 MHz BW channel from 5725 to 5745 MHz and second from 5745 to 5765 MHz.

For ePMP devices lower 20 MHz channel is major and  it's central frequency(5735MHz) is used in internal device tools.

So Main Frequency Carrier and Alternate ar considered as same channel.

I will open issue for that case and it will be fixed asap.

Thank you.

Hi Professor K,

Issue described by you in that topic has been already fixed in release 2.6.

Thank you.

The new 3.0 also will cause this to happen.


Thank you for your feedback.
I will check it asap and will be back.

Thank you.


I've checked issue and I did not o bserve it on 3.0 Release.

I've had UK Country code configured with Frequency Carrier 5755 MHz, and Alternate Frequency Carrier 1 5745 MHz.

And I get:

DFS Status	In-Service Monitoring

Thank you.