X-band motion detector interference with QO-100 downlink

  • Hi AMSATs,

    I have notice that at some urban locations there can be a strong interference at the 10 GHz downlink from what I believe X-band motion detectors. This happens for example at my office in Nijmegen, while in my hometown the same setup has crystal clear downlink signals.

    I just wonder if there are more amateurs with this problem as I get feedback from amateurs in urban locations that have similar experiences. I wonder if anything can be done against it, because those motion detectors are extremely close at 10.525 GHz.

    Below I put a link of an example motion detector:


    Kind regards,


    William Leijenaar PE1RAH

  • Hallo William,

    I don't know how the Dutch Regulations look like, in Germany the use of these sensors is not allowed. We have two ISM-Bands 5,8 and 24 GHz where 10 G-Motion Detectors can be used. 10 GHz-Systems from Asia are not legal. By the way, these oscillators are very unstable and noisy and drift with all parameters, temperature and supply voltage. The doppler effect based systems work with bad signals also.

    From my point of view interference in a narrow band system is hard to believe. These sensors have transmit power in the lower mW range. And the beam of a downlink dish is narrow too. Probably there are other noise sources in the envirement. Beside this, it is interesting to get more information. May be, for a test you can move the dish in different directions and locate the noise sources.

  • Hi Andreas,

    These are fully allowed for indoor use, and even well known companies like Bosch have these kind of motions sensors for sale.

    I looked it up, you can find the FCC regulation about it in the link below:


    The problem happens when a building full off those sensors are in the azimuth direction off the antenna beam. I have confirmed the source by changing the antenna direction and I also didn't believe it in the beginning. I spend quite some time trying to find the cause off "LNB oscillations", but later figured out it was actually comming from a 10.525GHz source from a nearby office building. After analyzing the signal pattern and searched the internet I figured out the existance off those microwave motion detectors. Even when the leakage is small, it is still more powerfull than the QO-100 downlink signal and slightly overloading the high gain IF stage causing problems with receiving.

    With kind regards,


    William Leijenaar

  • Hi William,

    probably you are right if this is carefully discovered. It surprises me, that there are some motion detectors in small area. Because these sensors "see" each other and trigger each other. The poor oscillator design leads to lock effects between the LOs. Drifting by, funny effects can be seen. This happened on 5,8 and 24 GHz also. I remember a customer who wants to check a low angle range with some 24 GHz-sensors. The signals in the spectrum moved towards and locked each other, horrible. Sorry, but I have no idea what to do.

    I will ask some friends if there are more observations and solutions. As I told before, this will not happen in DL.