We recently saw the below interesting post on a Linkedin group and obtained permission from the author to re-post it here.

Inquiries we made to various parts of the US government about this have not yet turned up any information. Some folks have had ideas, all of which we are forwarding to Professor Dovis to help with his further investigations.

Quite the mystery. If more develops we will post it here as well.  Watch this space!

GPS non-standard codes are being broadcasted?

In the past days we experienced the presence of spurious continuous wave interfering signals at 0.5 MHz from L1.

They appear and disappear during the local afternoon (between about 1.00 UTC and 6.30 UTC). Interference is measured at several Kms from our lab with the same power level so it is likely coming from space. Different equipments were uses for the data collections so it could not be antenna or front-end dependent. Could it be a case of GPS intra-system interference?

The observation of the spurious signal in the GNSS bandwidth has been confirmed by the colleagues at the Joint Research Center of the European Commission in ISPRA.

After several tests and investigations it has been identified as a signal coming from a non operational satellite with orbits similar to PRN 26, likely to be the Navstar 63 (Norad id34661). The harmonic nature of the interference let us guess that is a Non-Standard C/A code (NSC), as described in the GPS SIS ICD.

However, the strong power of the spurious signals is affecting the quality of the GNSS signals sharing the L1 carrier, the other GPS signals, the Galileo OS and Beidou as well.

Further investigations are going on to assess the impact on the receivers…