5 GHz RLAN interference with weather radars

The Czech Hydrometeorological Institute (ČHMI) has changed its procedure for sanctions in cases of interference with a weather radar in the shared RLAN band.

A new notice has appeared at http://radar4ctu.bourky.cz/Ruseni.html:

"We would like to draw your attention to the fact that from 1 October 2018 there will be a significant change in the processing of detected interference. Following discussions with Mr Jakub Rejzek of VNICTP z.s., who represents some RLAN/WiFi operators, and representatives of the Czech Telecommunication Office, hereinafter CTU, we have reached the following agreement:
after each measurement of interference sources affecting meteorological radars, RLAN/WiFi operators will have 48 hours to remove the interference without sanction, meaning that ČHMI will not forward a complaint to the CTU. After 48 hours we will carry out a follow-up measurement, and if we record interference from the same source, we will pass it on to the CTU without delay. Interference measurements, and the subsequent follow-up measurement after 48 hours, will always take place only on working days, so the 48 hours are working-week hours. For example, if we carried out an interference measurement on a Friday, the follow-up measurement would take place the following Tuesday at the same time. The above applies only to sources of interference that we are able to identify and that do not damage significant radar data. Sources of interference that we are unable to identify, or that significantly damage radar data, we pass on to the CTU immediately for resolution!"

This is a change in procedure that RLAN operators had been calling for. Although DFS is now mandatory under the RLAN standard ETSI EN 301 893, the possibility of interference with weather radars is not entirely eliminated. Operation on the affected frequencies, 5630 MHz Brdy and 5645 MHz Skalky, is not prohibited, and often the radar, when scanning, "sees" transmission sources at such a low level that operation is not affected. ČHMI has therefore chosen to publish the radio transmitters that are also potential sources of interference.

This useful information can also be read out by machine and, if the SSID or MAC addresses of the devices are known, passed on, for example, to a network operations centre. Unfortunately, ČHMI has not released any application that would allow simple data import, for example via SNMP. 

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Updated 5 March 2024