F400 ePTP link drops Reason: 53 (AP KEEP ALIVE RX STUCK)

So this link ran great at 40Mhz ePTP for a year or so, just perfect, not even a hiccup.

Had to bump it up to 80Mhz and it just started dropping with no reason given. Then upgraded firmware and seemed to be good again but lots of odd errors in logs. Support gives me beta software RC9 to try and errors still there but now DFS hits, DFS hits over and over…

So go back to 40Mhz channel , still running 5.4.1RC9 and it seemed fine for a few hours then started dropping the link every few minutes with

F=5620 11axahe40plus. Reason: 53 (AP KEEP ALIVE RX STUCK)

(oh and the occasional DFS thrown in the mix too).

So I looked and I see lots of posts with the keep alive stuck error but so far the only one I found with a possible solution was one person that changed from ePTP to TDD. However F400 doesn’t have TDD.

Anyone else seeing this on F400 and found a solution ?

I’ve seen the Reason: 53 (AP KEEP ALIVE RX STUCK) issue on a handful of F400 links. I’ve assumed that it is transient noise causing the issue, but on one particular link that was having a lot of this, I replaced the radios with AF5xHD and haven’t had a single issue or seen any evidence of noise.

At 1.5km an AF60-LR will be rock solid, except maybe if it gets iced over or packed with wet snow.

What happened here guys?

I am seeing this same thing on all my F400425 links. They work great as far as latency and capacity goes, but they are so unreliable as far as link uptime is concerned. I bought a bunch and they just sit in their box waiting for the firmware to become stable. It’s like the epm3k/f300 early days (years) all over again. Its a rare to see a cambium ptp link with an uptime of more than a couple of weeks. Although I have started seeing it with a couple of F300-25 eptp links on 4.7.

Does cambium look in here and care about this? I have opened a support ticket but they will tell me it’s interference, and when I prove there is no interference they will say it is intermittent interference lol.

Currently I set the netonix sw to bounce poe every few days at 4am, but it still manages to drop at peak times of course. I know I should buy a proper backhaul but this F425 link has no noise with like 800Mbps capacity and sub 3ms latency non-stop, until it drops and somewhere a kitten dies.


The AF60LR is awesome, up to maybe 1km or less.

I RMA’d my ptp550’s because they dropped and self rebooted their way through every firmware update for 3 years.


That’s terrible huh. The amount of stress the ptp550 links caused me has probably shortened my life by 37 hours. I bought the F400C radios to replace them and they are worse. I have one link that’s failover for a Siklu link, so hardly ever passes traffic, and ive never seen it with an uptime of more than 6 days. There’s hardly any noise and capacity is great, but they just drop for no reason. It hurts my wisp organ.
The AF60LR are great huh. We have some heavy rain so my 1km link drops rarely, but i’m sure if it was a little shorter it would never drop. I get -36 for 100% - it’s worth spending time getting it bang on. Good luck with it man

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… both of you are using those Netonix PoE ? Both of you didn’t try to replace it with something else ?

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