Ever since GPS became popular enough that receiver antennas began sprouting up in the same general area they have been interfering with each other.

A brand new case study from Chronos Technology shows how two GPS antenna can be 20m (60ft) apart and still cause problems.

By the way- it’s not a new problem and not just GPS antennas.  A 2002 Institute of Navigation paper explained how TV set antennas managed to jam GPS reception in a small California harbor.