DFS variance in 5.2 and 5.4Ghz?

We've been experimenting with 5.2 and 5.4Ghz for really close subscribers of less than a half mile.  Results are outstanding other than the usual problem with these bands -DFS.  For us, it seems like no matter which 5.4 frequency we use, the AP will stop transmission eventually because of DFS -and too frequenty.  The 5.2 band has been solid for us so far. 

My question is to those with experience in these bands, what is your experience with 5.4 and 5.2? Do you see a difference?  Do you seem to have more DFS hits in some parts of the bands and not others? The spectrum for us in these bands looks squeeky clean and we are not in TDWR territory.  My experience with DFS is that the hits are always false positives.  Most of us don't need 60Ghz products, we need the existing equipment that does a better job detecting the real thing.  But, I understand the challenges. 

Is this site a multi ap site? Do you use frequency reuse? Is it only one ap/ direction or on multiple aps?
You do not need to be in a tdwr territory to get hits from a radar station. Weather radar can go a long way if conditions are right.
If it seams random then look at self interference. And signal that is not the cambium signal style can trigger the DFS mechanism and finding it can be a real PITA!
Try placing an SM in spectrum scanning and get some data. On one of my APs I was seeing a sudden rise in DFS hits and we ecentually found it was a TP Link 5GHz bridge that a guy setup without doing a scan and properly setting power levels. Set to 30dB and 60degree 13dB gain antennas for 400ft of path! An SM clamped on each side of the truck ladder frame allowed us to find several of these issues.

Not saying your havung the exact same issue, but happy hunting!

We are just have an omni on a small 80ft tower feeding homes within a half mile of it.  5.2Ghz seems pretty solid in terms of available spectrum and lack of DFS hits.  5.4Ghz on the other hand had huge chunks of clean spectrum but it seemed like no matter which channel was used, DFS was a huge problem.  I was just inquiring about whether anyone else noticed this.  Dealing with these bands is an art into itself and it's nice to hear other peoples experience.  I'm sure sectorizing with extreme downtilt would be beneficial as well. 

Hi Douglas;

Can kindly share how you resolved it once you discovered the suspect interferer?  Were the parties willing to allow you access to their devices and/or make the adjustments on their devices?  Shouldn't the TP-Link product also obey DFS rules. Which will result in both parties backing off, i.e. the TP-Link and Cambium?   Wouldn't the Cambium black-list that frequency and then stay on the alternate channels you may have had programmed in the APs?

Shouldn't eDetect and an automatic channel scan (ACS) allowed you to determine better channels to use?  Since the TP-Link would have always been transmitting on the same channel. 

Will this now almost make you the local regulator for the frequencies, for everyone who starts to have APs around in the same 5.4Ghz space?

Hi Nathan;

Our experience with the 5.2GHz band have been very good to great.   We've had real success with it.  We kept using the 5.2GHz frequency after migrating from the Canopy PMP100 5.2 series.  The Canopy 5.2 really was stable and rock solid.  We've found the same with the ePMP series.  The only problem we had in the past was the distance limitations imposed at that time.  In the ePMP series and changes to the rules (I guess) have allowed for further distances to be achieved.  If all of your clients or SMs are in LOS (conditions), then I would say you won't see any really loss / disadvantages.  With the distance and/or radius that you are trying to service, I don't see why the 5.2 band will not work for you really good.

Using an omni however is something that I can't really speak for.  That in itself may be an issue for either band.  But the risks of interference may be far less in the 5.2Ghz band.  If possible, and if you wish to stick with the 5.4Ghz band, then maybe splitting the omni into 3 x 120degree sectors may be better.  Or, re-evaluate if you really need to have an omni to service everyone.  If budget is not a factor and other tower restrictions don't exist, then consider using sectors.   Another possibility if the tower permits, you could still sectorize using the non-GPS units.  You may still achieve your objectives and have a low cost for implementation.  Some sectors can then use the 5.4 band where there is less / no DFS and other sectors can use the 5.2 band.

With DFS and ePMP we had the same issue you experienced to some degree.  The DFS is a real pain.  However, we've found the recovery time for the ePMP (along with their firmware updates) had allowed for a faster recovery.  In addition, being able to configure alternate channels was a great feature that really helped us further to reduce the outage window imposed by the DFS rules.

One limitation we had found with the 5.2 band was that if you didn't have LOS and you had an nLOS condition, it would not perform well.  But that was in our Canopy 5.2 era.  So far we've stayed away from that type of installation.  Not sure how ePMP will perform with 5.2Ghz and nLOS and distance.


We have some APs that are riddled with faulse DFS hits no where near the TWDR channels. We have been working with Cambium support and their advice is to run an ePMP 2000 to filter out of channel noise. Were going to give their suguestion a go and see if there is any improvement.