This is not really apropos radio broadcasting, but it is about radio and it has a lot to do with engineering. Back in the day, as a young man out to do whatever it was, I ended up being stationed on Guam, working at the Coast Guard radio station there. That was interesting work, to be sure, but every morning and evening, either on my way to or from work, I would drive by this, which looked very interesting:
AN FRD-10 NAVCAMSWESTPAC, Guam
I had to lift the photo from a Navy Radio history site. Back in my day, aiming or even possessing a camera around this area or building would likely inflict the extreme ire of the Marines, who attentively observed the area and were ready to call down a painful lesson to all not obeying the “NO PHOTOGRAPHY ALLOWED” signs.
Nick named “The Elephant Cage” it is a Wullenweber antenna used for high frequency direction finding (HFDF) and was part of a system called “Classic Bullseye.” There were several of these systems across the Pacific Ocean, and they all worked together using a teletype network. The Army-Air Force version was called a AN FLR-9, which was slightly larger.
AN/FRD-10 antenna layout
There were two concentric rings of antennas, the tallest being the closest to the center building and used for the lowest frequencies. It covered from about 1.5 to 30 MHz. The rings consisted of several individual antennas, all coupled to a Goniometer with coaxial cables cut to identical lengths. The outer ring had 120 vertical sleeved dipole antennas, the inner ring consisted of 40 sleeved dipole antennas. The inner ring of towers also contained a shielding screen to prevent the antennas on the other side of the array from picking up signals from the back of the antenna. A radio wave traveling over the array was evaluated and the Goniometer determined the first antenna that received the signal by comparing phase relationships. The ground system was extensive. Immediately under the antennas was a mesh copper ground screen. From the edge of the copper mesh, buried copper radials and extended out 1,440 feet from the building.
The effective range for accurate DF bearings was about 3,200 nautical miles, which equates to about two ionospheric hops with the angle theta between 30 to 60 degrees referenced to ground.
It was quite effective, it only took a couple of seconds to get a good bearing. If the other stations on the network were attentive, a position could be worked out in less than 10-15 seconds.
AN FRD-10 ground diagram
It is a little hard to read, but this is the ground layout of the AN FRD-10 CDAA. The transmission lines to each antenna are shown, along with the ground screen and building in the center of the array.
We Coast Guard types used this mainly for Search and Rescue (SAR) and the occasional Law Enforcement (LE) function. I believe we actually saved a few lives with this thing. I found the Navy operators to be very helpful, I think some of them enjoyed the change of targets from their normal net tripping.
The navy operated AN FRD-10s at the following locations:
- Imperial Beach, CA (south of San Diego)
- Skaggs Island, CA (north east of San Francisco)
- Hanza (Okinawa) Japan
- Waihawa, HI
- Finegayan, Guam
- Adak, AK
- Marietta, WA
The Air Force/Army installed AN FLR-9′s in the following Pacific Locations:
- Missawa AB, Japan
- Clark AB, Philippines
- Elmandorf AFB, AK
Basically, there was no corner of the Pacific Ocean that could not be listened to and DF’d. Some people look back nostagically at the cold war, when we “knew who the enemy was,” so to speak. I am not one of those. They either didn’t really know the enemy, or have conveniently forgotten some of the less endearing qualities of the Soviet Union.
I believe all of these systems have been decommissioned and most have been taken down and scrapped. The National Park Service studied the Waihawa, HI system as a part of their Historical American Building Survey (HABS HI-552-B2) (large .pdf file) before it was torn down. Good technical description and building pictures. Near the end of the report, it is cryptically noted that:
Beginning in the mid-1990s the NSG (ed: Naval Security Group), noting the absence of Soviet targets and wanting to cut costs and change the focus of its SIGINT collection, began closing FRD-10 sites… Undoubtedly, since the September 11, 2001 terrorist attack on the World Trade Center and the Pentagon, listening posts have gained importance and most likely increased in number and sophistication. The FRD-10 CDAA at NCTAMS Wahiawa ceased listening in August 2004; it can only be assumed the closure occurred because there was a better way to do it.
Indeed.
The Guam site has been striped out and abandoned, the latest photo I can find is from 2008:
Abandoned AN FRD-10, Finegayan, Guam
And people think AM broadcasting is expensive…
I remember something like this outside of the Champaign-Urbana metro area in Illinois. As I recall, it was only a single ring of antennas, though.
That was build by the University of Illinois shortly after the plans were captured from the Germans in 1945. They studied the Wullenweber design extensively. I think it was abandoned sometime around 1980, it might still be standing.
Interesting. I am curious as to who the contractor was?
I believe the contractor was ITT Federal for the Navy systems and Sylvania for the Army/Air Force, although a lot of the equipment for the Navy system was made by Sylvania, things like antenna couplers, etc.
I worked at this site for 3 years from Dec. ’72 to March ’76. There is more information posted here than we were allowed to know when working at the site. The Naval Security Group rating at that time were CT’s (Communications Technicians) and there were 5 branches CT-R, CT-C, CT-T, CT-M, CT-A. They were sort of their own organization within the navy with the required security clearances to deal with the needs of the Naval Security Group. The C’s handled two way communications within the rating, the T’s dealt with the digital modes of communications, the M’s maintained the equipment, the A’s handled the administrative functions, and the R’s were collections (I guess because the C’s were already spoken for). The R-branchers were Morse Code operators and worked in the DF part of the operation. Today the CT personnel are known as Cryptologic Technicians. There was an armed Marine guard at the entrance door who would only allow you in if you displayed the proper ID tag that must be worn at all times when in the building. After getting past the first door there was a second door that required a security code to get past. Once inside there were various areas within the building that also required security codes to get past in addition to the proper ID tag that was color coded to show what areas of the building to you were allowed access. In the rare instances when private contractors were required to work in the building, all equipment had to be set to a defalt setting that would not give away their intended purpose, or if that was not possible it was covered so it couldn’t be viewed.
I remember the CT’s well. I was there in the late 80′s early 90′s when Classic Wizard was the primary focus, however, the Wullenweber antenna was still in use. It was a fantastic engineering feat and it is a shame that it was dismantled.
I believe the AF is still operating the AN/FLR-9s The one we had at Misawa AB in Japan (FLR-9a) was a newer one with a few differences than the stock -9. Our friendly “Bear” still operates a lot of HF equipment and it pays to know from where it is working. If you check Google Earth you can quite clearly see the one at Misawa. Look Northwest of the runway and across a small lake to find “The Hill” as sigint facilities are often called..
Dave, I didn’t know that the AF was still using CDDAs, that is interesting. I suppose there is more Bear air/army traffic than naval activity these days, as most of their old fleet is now razor blades.
I know that the FLR-9 at Clark was turned into an amphitheater after the US pullout in 1991.
Very nice article. I spent 5 1/2 years of my life working in the Elephant Cage on Guam. First tour was 1978-81. During my second tour from 1992-94 I ran the operation. Several things went on in the Naval Security Group Department (NSGD) Guam. HFDF was one of the centerpiece missions that faded away due to changes in communications technology. When HFDF was still front burner we spent most of our time tracking Soviet planes and Naval targets, surface and subsurface. Other countries were also in our target list. And, we supported Search & Rescue (SAR), working closely with the Coast Guard and other services to assist in locating distressed ships or aircraft. Fix accuracy Pacific HFDF Net was always an issue due to potentially long distances to the target, signal drift, and atmospherics. Fixes were more often expressed as elipses, within which targets could be found. Sometimes the elipse was quite large, so for SAR ops it was often best to send a rescue ship or aircraft out on a line of bearing (LOB). During a SAR mission we ideally wanted our target to go up on a specified HF frequency and communicate a long count of numbers. That way the Pacific HFDF Network could keep copying and triangulating for a better fix. Getting a fix on the Soviets or “Ivan” was not so easy. Over time they migrated to communicating with packeted burst signals that were often over in milliseconds. Each signal had a unique signature that could be assigned as a specific target. For moving targets accurate fixes were problematic but if we got enough hits as they moved along then we could provide general locating data and a probable course/speed. It was a game of electronic cat and mouse. S. Wuelfing got the CT branches a little off or his info may have been dated. He said a CT-C was a communicator. That may have been true once, but when I was on active duty CTO’s were communicators. And, he left off CTI’s, the Linguist branch. Before getting my commission in the Navy I was a Marine CTI. The Navy and Marine Corps always worked closely together. Navy CT’s comprised the Naval Security Group Command while Marines with CT-like MOS’s were the Marine Support Battalion and Radio Battalions. We all worked together at many NSGD sites. In addition to HFDF in the Pacific the we also had the Atlantic Net and there was an Indian Ocean site on the island of Diego Garcia. We also worked closely with allied countries, such as the UK, Canada, Australia and a few others who joined in the effort to target Soviet aircraft, ships and submarines. A primary concern during the Cold War was tracking their ballistic missile submarines that lurked under the Arctic ice shelf close to the U.S. and our allies in the Northern Hemisphere. That could be another whole story. A great book on how CT’s were used by the U.S. Navy and the National Security Agency (NSA) onboard our submarines to counter the Soviets is “Blind Man’s Bluff.” CT’s or “Spooks” as they were known back in the day were involved in many missions vital to U.S. security. It was a privelege to have been able to serve in the Naval Security Group and to have gotten to know many of the brilliant and interesting people who dedicated themselves into the cause of freedom.
Thanks for the interesting comment, Bill. My service on Guam was between yours. By your second tour, the Coast Guard communications station (in building 150) had been closed down. You may have received some occasional tasking from MARSEC, located down at Apra Harbor. I always enjoyed working with the Navy guys. Toward the end of my tour, we had a couple of courtesy visits from NSG Hawaii. I got to talk with a couple of the CTO’s and they had interesting things to say.