1. Russia suspected of jamming GPS signal in Finland.https://www.bbc.com/news/world‐urope‐46178940. Accessed 12 Nov 2018
2. South Korea issues warning over suspected North Korean GPS disruption
3. Military GPS jamming is disrupting US aviation – and it's getting worse.https://www.linkedin.com/pulse/military‐gpsjamming‐disrupting‐us‐aviation‐its‐getting‐guy‐buesnel. Accessed 8 Mar 2018
4. Can LORAN meet GPS backup requirements?
5. Question: Alternate position, navigation, timing, APNT? Answer: Eloran