C5x problems - keep changing channels

I have auto channel turned off on the C5x. However it still keeps switching channels and I get a notice that says "RADAR SIGNAL DETECTED, Changing to different channel.

So if auto channel is turned off, why is this happening??


You are using what’s called a DFS frequency, 5245-5340 or 5480-5730, these frequencies we are secondary users. Meaning that if your equipment detects a signal that indicates that there is a Radar station using the frequency then, by law, the equipment has to change channels (minimally temporarily).

Now there is such a thing as false DFS hits, they can happen because of various things and are largely because the regulations for detecting DFS hits forces equipment to have a broad range of things it has to look at.

There are a few ways to minimize the chances you will get false DFS hits though, primarily correctly setting your antenna gain in your radios. You can also check for local weather radar locations and airport radar which there are a few maps floating around the internet that shows which frequencies they are using. Lowering your transmit power can help as well, that will help you dodge issues with reflections of your own signal triggering false DFS hits.

That said, you can go months/years without having a DFS hit then suddenly get a slew of them, normally this settles down after a day or so, but sometimes there’s just some local noise that will trigger your equipment for a certain frequency. Unfortunately, DFS is forced to be really sensitive and false hits are a fact of life.

If the C5 is seeing another radio using TDMA even on another adjacent channel it will detect a false radar hit. Be very careful about overshoot and other radios in the path. Use the lowest power/gain to achieve the signal/phy rates you need.

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We must not forget cellular towers and the RF interference they provide free of charge. Especially now with 5G rolling out to more and more towers. The amount of power cellular uses will shock you when you apply the “minimum amount of RF needed to complete the connection” is applied.

Other things that trigger are harmonic-based in nature… signal 1 plus signal 2 = intermod, possibly in your selected channel.

We recently experiences a HUGE amount of rolling interference that all but took down our P2MP system. Our P2P was also affected, but since they use the channels differently, it didn’t take them out of commission…and then…a few hours later… nothing… RF ghost town.

We had also considered that this might be a directed (on purpose) jamming event.

Also, we recently learned that another company that makes equipment like Mimosa apparently is able to run channels at 10mhz wide instead of the normally seen 20, 40, or 80… Mimosa hardware detects this… you likely won’t see it on the built-in spectrum view… I am aware of 2 competing WiSP providers in our area that use this specific equipment… None of their P2MP appears on the spectrum view, but their primary links do, and they’re using 100-250’ towers with a commanding view…

So… it’s not fun, but there’s a huge amount of potential interference that can (and does) trigger a channel change when using DFS frequencies. This is a risk of unlicensed users and additionally with the FCC regs on how DFS must automatically sense and move when it picks “something” up. If the primary users had something in their signal we could key off of for a legitimate channel change need, that would be nice…I don’t see that happening.

As noted, there’s a few lists out there that have the KNOWN radar frequencies listed…it’s rather extensive, and if you’re in a high usage area RF-wise, manually adding these other frequencies to be blocked from your use, you’ll find you STILL get radar channel changes! Unless you block all DFS channels… That would not be helpful in the long run.