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I am responsible for Mono-pulse Secondary Surveillance Radar (MSSR) system that resets itself after a watchdog failure. So far I have found the following:

  • An unwanted number of replies are received by it.

  • A noise test was also done but the test didn't find any interference,

  • The system is running smoothly, but suddenly from west direction an excess number of replies are received which cause my MSSR to reset.

  • this interference time is only occasionally, it come out whenever they wanted,

  • The Frequency Allocation Board team has been contacted to find out the source of this interference, but since it happens only occasionally they are also unable to find it.

If someone has experience on it or face the same issue kindly reply as soon as possible.

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    $\begingroup$ @Asifa Liaqat Welcome to aviation.stackexchange.com. I've edited your question so it is better readable. I hope my interpretation is correct, please make further modifications if needed. $\endgroup$
    – DeltaLima ♦
    Commented Nov 7, 2019 at 8:28
  • $\begingroup$ <<this interference time is only occasionally, it come out whenever they wanted>> who's "they"? $\endgroup$
    – Federico
    Commented Nov 8, 2019 at 9:23

2 Answers 2

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1) What I expect is that there is a transmitter (or multiple) on 1090 MHz to the west of the RADAR that does not conform to the ICAO standard. I would start by looking at the decoded replies that the MSSR is receiving (not in ASTERIX format, but raw datagrams format. I believe the INDRA MSSRs can provide this). This may give a hint as to what the cause is(e.g. a certain 24 bit address range, certain downlink formats only, received power level, etc.).

2) Are there any military bases to the west of your RADAR? Or RADAR manufacturers? A transponder manufacturer? It may help to contact them. (Likely they will deny any experiments are going on, but the problem may suddenly disappear. It happened before).

3) Atmospheric tunneling may cause a specific transmission path only to exist under certain weather conditions (e.g. inversion layers) . Can you find any correlation between the interference and weather conditions?

4) Do you have multilateration systems covering the same area. The multilateration system may be able to locate the source.

If nothing else helps, you may have to install an array of 1090 MHz receivers and multilaterate the source.

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  • $\begingroup$ MLAT system is installed and when interference came over MSSR, MLAT also received the same interference and yes at west side there is military base but sometimes this interference also received from east side $\endgroup$
    – Asifa Liaqat
    Commented Nov 11, 2019 at 7:26
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I have had a similar problem with a Thales RSM970S where a (hidden) QRSLS alarm caused a watchdog failure. The best we could conclude was that the interference was caused by non-compliant wireless equipment, but tracking the user proved to be impossible. With the help of the OEM we modified the bite alarm reference file to reduce the systems sensitivity to this issue (outside of the scope of normal optimization or LRU maintenance). The modifications had no negative impact on the radar's aircraft tracking, confirmed with SASS-C analysis.

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  • $\begingroup$ I've encountered wireless security video systems from China that use 1090 MHz. They cause serious interference with secondary radar. You can imagine the joy when a local restaurant owner near an airport secured his restaurant with such a system... There are also video transmission systems used on drones (FPV) that operate in the aviation L-Band (e.g. Mateksys 1G3), close to the SSR frequencies and some PSR frequencies (although the PSR doesn't care much). $\endgroup$
    – DeltaLima ♦
    Commented May 14, 2020 at 8:16

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