[IGSSTATION-7819] IGS station OP71: back to nominal operations

[Pierre Uhrich]

Dear IGS Colleagues,

One year ago, I had alerted that the GNSS reception of OP71 at Observatoire de Paris (OP) was jammed by an interference of unknown origin. It took us one year to solve the issue.

To make a long story short, here are the major points.
- The issue was a typical out-of-band jamming by a powerful signal in the band 1515-1560 MHz (just below the GNSS L1-band).
- Only OP multi-GNSS stations were impacted. But this was mostly due to the largest bandwidth of antennas used for collection of multi-GNSS signals. The old GPS-only antenna bandwidth was apparently sharp enough around GPS carrier frequencies to downsize the power of the jamming signal preventing LNA saturation. This is why the GPS-only station OPMT was not affected.
- The responsibility of the RF spectrum for France is in the hands of Agence National des Fréquences (ANFR). A formal complaint was raised by OP to ANFR early 2019. The jamming source was identified to be an institutional body from penitentiary administration. Their aim was to jam all communications in all bands (GSM, WiFi, satellite, …). It was not easy to organize a common test series experiment with the company in charge of the transmitters, but it finally took place twice during Summertime.
- We eventually reached the point where the current jamming power as received in OP is restricted to + 3 dB with respect to no jamming signal at all. We extensively tested that this power level was not disturbing GNSS L1-band reception anymore in OP, according to our own computations and for the current equipment at 10 ps level. Therefore, we consider that OP71 station is fully nominally usable again since 1st December 2019.

For those of you interested by this kind of issue, there is a paper available in ITU Journal describing the irruption of the jamming signal in OP, the effect on our multi-GNSS stations, and the monitoring we put in place for surveying the spectrum below L1-band: https://www.itu.int/pub/S-JOURNAL-ICTS.V2I1-2019-1

Meanwhile, the temperature monitoring control system was upgraded in the OP operation room, resulting in a decrease of the diurnal effect in OP71 data.

We updated the OP71 log file accordingly, here joined.

Any question or comment is welcome.
Best regards.
P. Uhrich



Dr Pierre Uhrich

Ingénieur-Chercheur LNE		Pierre.Uhrich at obspm.fr

LNE-SYRTE	
Observatoire de Paris, Université PSL, CNRS, Sorbonne Université
61 avenue de l'Observatoire
75014 Paris
France

Tél.: + 33 (0)1 4051 2217
Fax.: + 33 (0)1 4325 5542


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