The mystical radar

Long time dream went true during the last weekend. I was able to capture an DFS ( Dynamic Frequency Selection ) or radar event in the wild.
First time I was able to detect a real world weather / rain radar from DWD (
https://www.dwd.de/DE/Home/home_node.html ) with Ekahau Analyzer, Pro and Sidekick.

Since the availability of the upper 5 GHz bands their usage often is blocked by the mystical radar.

Too often I have to ask WLAN operators why they don’t use the channels above 100 or between 120 and 140. Its because of the radar they reply. I ask back: “Did you measured any radar ? “Yes there are radar events in our syslog file several times a day or week”, they claim.
The radar events are reported by the WLAN manufacturer themself. 

Does it mean this is the truth ? ¯\_(ツ)_/¯

Because of that I was looking desperately to double check radar events with a spectrum analyzer.

With Version 1.2.x Ekahau finally created a radar classification feature for their Ekahau Analyzer App.
(https://www.ekahau.com/products/ekahau-connect/analyzer/) .

I was able to proof that the detection works correct based on the radar event generator of the WiFiMetrix V.2 I’m lucky to own (http://wifimetrix.com/the-dfs-project/

It generates FCC pulses only, but it’s better then nothing.

What I really was keen of is capturing radar events in the wild. I tried it at airports but found nothing except some nice OFDM channels.

Then I started to search about weather radars. It came to rain detection radars. 

There are several manufacturers globally.

(https://www.environmental-expert.com/companies/keyword-doppler-weather-radar-63671

Some use 5600 MHz frequencies for rain drop reflection detection.

But who’s is operating these?

In Germany in terms of weather you will stumble over DWD (Deutscher Wetterdienst) and this interesting PDF- document.

(https://www.dwd.de/SharedDocs/broschueren/DE/presse/wetterradar_pdf.pdf?__blob=publicationFile&v=7)

I planned to visit the location next to Berlin in the nice village of Prötzel. First try failed.

I didn’t found the location.

That’s why one should check this document with the exakt GPS position. 

(https://www.dwd.de/DE/derdwd/messnetz/atmosphaerenbeobachtung/_functions/HaeufigGesucht/koordinaten-radarverbund.pdf?__blob=publicationFile&v=5)

Last weekend I was lucky, found the place and made a foto to prove it.

Img. 1. DWD weather radar Prötzel

Of course I also fired up the Ekahau Analyzer and after I little time (some felt minutes) it really reported radar at ch 128 as expected from theory ! Yeah ! See screenshot for evidence.

Img. 2. Radar event classified with iPad, Ekahau Sidekick and Ekahau Analyzer App at a maximum receive power of -30 dBm

The normal fox hunt method to switch OFF and ON the signal source and double check that the correct signal was captured is not useable here, I guess.

I used the Ekahau Pro RTFM spectrum magnifier to get a little closer to ch 128.

If you compare the intrinsic line of Img. 3 and 4 you may see they are quite similar, right ?

I´ll take that as a proof this time. 

May be one of the US colleagues could additionally double check if FCC 0 is the pulse for weather radar.

Img. 3. Captured signal at DWD radar Prötzel at ch 128
Img. 4. Captured generated radar pulse FCC 0 at ch 128

Think it could be interesting to find out what the exact “impact radius” of this weather radar station would be. This radius should end at a power level below -62 dBm.

Thats what I learned from a WLPC presentation by David Coleman in 2019 in Prague. 

As a start I can say the signal is not able to catch 2.000 m away in one direction. So further investigation is ongoing. Stay tuned folks.

WLPC presentation by David Coleman in 2019 in Prague. The whole thing is worth to view of course but for impatient people start at minute 15:30.

Ein Gedanke zu „The mystical radar

  1. That’s very cool to see that radar in action. I use DFS channel on home wifi and it’s very stable and best of all, impervious to my neighbours’ wifi who blast away on the usual unii1 and unii3. Thanks for sharing this.

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