The 1,200-Foot Antenna That Listened to the World

In the 1960s, the US Air Force and US Army constructed eight huge antenna systems, each the size of the Pentagon, to conduct HF Direction Finding (HFDF) and intercept operations. The FLR-9 antenna systems, sometimes referred to as the "Elephant Cages" were Circularly Disposed Antenna Arrays (CDAAs), or Wullenweber antennas. The eight Air Force and Army FLR-9 systems formed the IRON HORSE HFDF and intercept system. Sixteen US Navy CDAA systems, the FRD-10, of a different design but of a similar scale and complexity were also deployed around the world in the BULLSEYE system. These systems supported National Security Agency (NSA) SIGINT missions for decades 0:00 Introduction 0:58 Overview of the FLR-9 "Elephant Cage" & FRD-10 antennas 1:57 Origins: German WWII Wullenweber antenna design 3:04 How the goniometer & direction finding work 4:26 Phased combining: sum & difference signals 5:59 Post-war Soviet adoption: the "Krug" system 7:33 US Navy R&D: Multi-band intercept & fixed beams 9:57 NRL experimental CDAA at Hybla Valley & Sputnik tracking 13:46 The US Navy AN/FRD-10 system design 15:47 Sugar Grove Navy Station & diversity HF reception 17:26 The USAF & Army AN/FLR-9 architecture 19:39 Antenna bands: sleeve monopoles & inner bow-tie dipoles 21:24 Massive scale: comparing the array to the Pentagon 22:26 Sleeve monopole RF design & bandwidth 24:08 Band C bow-tie dipoles & impedance matching 25:29 The underground coax infrastructure & phase matching 27:36 Inside the roundhouse: multicouplers & line tuners 30:58 Beamforming mechanics & nanosecond time delays 37:38 The rotating goniometer & angle resolvers 40:45 Sum & difference null processing for precision DF 44:16 Operations tunnel & distribution to intercept stations 46:18 The Joint DF Network & remote station tasking 48:56 Strategic deployment: Iron Horse network & pacific ring 49:53 Decommissioning, demolition & site conversions 52:02 Maintenance challenges & transition to modern DSP 54:49 Elmendorf drone video walkthrough 56:38 Audience Q&A: Bow-tie polarization & ionospheric faraday rotation 59:16 Audience Q&A: Monopulse radar comparison 1:00:43 Tracking Soviet burst transmissions: Project Boresight & Bullseye 1:03:48 Q&A: Cable loss, sensitivity & 75-Ohm hardline 1:06:17 Q&A: Vertical angle of arrival & multiple hops 1:09:44 Q&A: Soviet Krug systems & conclusion Vienna Wireless Society is one of the largest and most active Amateur Radio clubs in Northern Virginia. Club meetings are conducted in hybrid mode, with remote attendees joining via Zoom, and are open for everybody, anywhere. To learn more, please visit our website: http://viennawireless.net/wp/ To receive notifications about meetings, and participate in discussions and activities, please join the Club: https://viennawireless.net/wp/join/ You can also browse the archive of past presentations: https://viennawireless.net/wp/meeting... To receive notifications about new videos and streams, please subscribe to the channel. The video has been published on the channel with permission from the presenter, as a service for Vienna Wireless Society amateur radio club. The presenter holds full responsibility for the content of the presentation. If you believe that the video infringes your copyright, please contact contact@viennawireless.net To use this video in your content or play at a meeting, please send an email to contact@viennawireless.net #HamRadio #ColdWarHistory #Antenna #AmateurRadio #RadioHistory #MilitaryHistory #ElephantCage #ANFLR9 #Wullenweber #DirectionFinding #sigint #RFEngineering #AntennaDesign #vws #ViennaWirelessSociety #hamr