Cold War Listening Post Antennas

With a UHF antenna, it is easy to rotate a directional antenna to find the bearing to a transmitter. But at HF, it is more common to use an array of antennas that you can electrically switch as well as analyze the phase information between the elements. [Ringway Manchester] has a look at the “elephant cage” antenna used by the US Iron Horse listening network from the 1950s. You can see a video about the giant antenna system, the AN/FLR-9.

Technically, the ring of concentric antenna elements forms a Wullenweber antenna. The whole thing consists of three rings built on a ground screen nearly 1,500 feet across. The outer ring covers from 1.5 to 6 MHz or band A. The band B ring in the center covers 6 to 18 MHz. The inner ring covers band C which was from 18 to 30 MHz.  Band A was made up of 48 monopoles while band B used 96 elements. The much smaller band C elements were 48 pairs of horizontally polarized dipoles.

These listening posts could, together, locate an HF signal up to 4,000 nautical miles away. The Wullenweber design, as you may have guessed from the name, originated with the German navy during World War II. It found use in several other systems, although they are relatively rare today, with all of the AN/FLR-9 sites gone.

Cold war hardware is always interesting even if sometimes terrifying. If you think a giant shortwave direction finder is high-tech, you should check out how the Russians bugged IBM Selectric typewriters for a long time undetected.

32 thoughts on “Cold War Listening Post Antennas

  1. Not sure if I missed something but:
    1.5 to 6 MHz is band A.
    6 to 18 MHz is band B.
    18 to 10 MHz is band C.

    The way it’s written, it seems like band B and C overlaps by a lot?

  2. When I was in college at the University of Illinois, we drove around in the country a lot and we ran across one of these. I don’t remember if the antennas where still there in the early 1990’s or not. I never really looked into it at the time. The site is still there and marked as a museum on Google maps… 40.04963, -88.38067. You can find info by googling “University of Illinois wullenwebber array”. Cool history.

  3. Should really say ‘old cold war’ or ‘previous cold war’.
    Anyway, seems you can do all your spy stuff on HF since it’s not monitored now :)
    Unless… do they have elephant cages in space now? Or how do they do it now?

  4. Direction finding at HF and lower frequencies can be done at a smaller scale with a loop antenna, which can be handheld sized, similar to UHF direction finding. The loop antenna would have a variable capacitor in parallel to tune it to the desired frequency. This setup would be limited to monitoring one frequency at a time.

    AM radios with loop antennas were used to listen to stations that the Germans were trying to jam during WWII, making use of the antenna’s directionality.

  5. Had these in the Navy also. One at Naval Communications Station – Nea Makri, Greece. Was Crypto tech there 1971/72. Base was closed in 1975, I think. Wullenweber was dismantled, base turned over to Greek government. It is a training facility for firefighters now, pixellated for some reason on Google Earth.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.