Image: NASA

Many thanks to SWLing Post contributor Scott Gamble, who writes:

Hi Thomas –

An interesting article was published in the most recent issue of Inside GNSS magazine that suggests that the US Military has been using an obscure field in GPS broadcasts to deliver encoded messages, potentially for use by intelligence agencies.

The article “The Empty Field That Wasn’t: GPS, OTAD, and Two Decades of Encrypted Messages,” by Steven J. Murdoch of University College London, is available via the link below:

https://lsc-pagepro.mydigitalpublication.com/publication/?i=865273&p=62&view=issueViewer

Scott