I have a very short (40m) PTP link using a pair of SXTs, but when using DFS with Radar Detect, it detects radar on each channel the AP decides to use.

This link is in a very RF dense environment, there's all sorts of Canopy, Ubiquiti and other MikroTik gear in the area (but not co-located)... could it be that one of these other platforms are sending out a RF signature which is being detected by MT as radar?

Both SXTs are running 5.14, in nv2 mode.

A few others have posted with similar problems. I think they rolled back to an older version.

Oh No, do not tell me MikroTik have got the same problems as Ubiquiti and Deliberant with very small amounts of interference being detected as Radar, Ubiquiti have almost cured their false radar detections.

I have just purchased 2 x Sextant's and 2 x SXT's, I would not have wasted my money, if they do not work or detect false Radar, i am not messing about they can gor right back.

Everything was fine with the old Atheros chipset radios, the new Radios are just too sensitive and detecting the slightest interference as Radar, when there is no Radar anywhere near.

I tried upgrading another router (with an abg-only radio) to v5.14 and it doesn't detect any Radar.

Yet another RB -this time with an R52N radio- was detecting Radar indoors!

The Atheros chipset makes available to the OS what pulses it sees on the Physical RF layer - it is then up to the OS to decide how to interpret those messages. But different chipsets provide different levels of data, some better than others. So it is also hardware dependent as well as down to the OS's method of analysing the data provided.

The AR5416 chipset for example can only report if it has what it thinks is radar in the primary 20MHz channel, if you enable 40MHz on such a chipset, it only reports radar on the primary 20MHz channel it ignores the secondary 20MHz channel. Later chipsets such as the AR9130/AR9160, AR9280/AR9285/AR9287 and AR93xx/AR94xx report both pulse width and RSSI level, making it much easier to figure out if the noise really is a radar or not.

I have one client that uses Ubiquiti links and at one site if we enable DFS it never finds a clear channel as it claims they all have Radar interference on every channel, when this is not true.

These later chipsets are all detecting interference as radar, even on the bench in the workshop, it even detects is own clients as radar, Ubiquiti have stopped it with Beta 12, but with beta 12, they will not work when both are in AP WDS mode, instead of AP WDS and Station WDS, Ubiquiti are working on the fix for this bug, when that is fixed they will have good working radios again, something we have not had since firmware 5.2

MikroTik need to get their finger out and fix it on their radios.

same here. I have an Omnitik here that is regularly detecting radars. Other 5Ghz devices (Lancom) do not see these radars.
Some month before ubiquiti devices behaved similarly here - but opalit is right latest firmware (beta) fixed this.
I hope Mikrotik will fix this bug also. If not, the mikrotik devices will be useless for me.