Aeronautical radio beacons & maps, Finland 1950s - Military Airfield Directory
What is an ILS and its different component? | AIRPORTS AUTHORITY OF INDIA
ATPL Theory - Marker Beacons Marker Beacons are stations on the ground. When you fly overhead they will let you know by means of a visual or a sound (can be both).
Communication and navigation services
What's The Maximum Distance For IFR Procedure Turns? | Boldmethod
navigation - What are outer marker horizontal dimensions at 3 degrees ILS path? - Aviation Stack Exchange
Marker Beacon (Wikipedia Reference) | PDF | Geography | Wireless
RNAV – BruceAir, LLC
LOM - "Compass Locator at the Outer Marker" by AcronymsAndSlang.com