If you’re 18 and at a rave party, it’s not good to feel alone. You definitely need help. If you’re 69 and at home, it’s 0300, and you hear strange noises in your house, it’s not a good feeling to be alone then either. The chances are you really need help. And if you’re standing before a divorce judge and your attorney has just quit your case… without a doubt you need more help than you can imagine. However, if its 1942 and you’re treading water at sea, alongside a downed Mustang, the chances are that although you may feel alone you are not alone. Given the examples just stated, I would rather be treading water at sea, next to my downed fighter plane, than in any of the other situations.

Why?

Because thanks to the U.S. Army Signal Corps I would likely be treading water along side of an SCR-578.

What’s an SCR-578, you ask?

Well, if you can manage to get it and you into that damned inflatable dinghy before that shark sniffing at your boots decides to see what an Army Air Force pilot tastes like, you’ll soon find out. What you’ll find out is that you’re now sharing your lifeboat with your own private Gibson Girl. And this little beauty may save your life.

As Signaleers, most of us think in terms of our branch being responsible for prosaic means of communication… methods and systems meant to connect people in order to foster better command and control of a battle space. But that’s not always the case. Regular readers of this website know that the Signal Corps gets involved in lots more than just producing and operating combat radio systems. One of the more interesting areas—one that has received surprisingly little recognition—is the area that deals with survival radios. If you’re in trouble and need to be able to reach out and touch someone, the chances are that the radio or telephony device you do it with had its start with the U.S. Army Signal Corps, back in World War II.

When it comes to survival radios however, to be fair, the Germans seem to be the first to have figured out that having spent a ton of money training a man for combat, spending a little more to save him after he got into trouble was a far better use of money than leaving him to die and then retraining a replacement. And since back then, when they were perambulating over how to solve this problem of soldiers dying on the job by some means other than being shot, most of the trouble that came along where lives could be saved had to do with naval vessels being sunk at sea, well… it made sense to find a way to help those who found themselves floating around in the vicinity of a downed ship call out to the world and say ‘come rescue me.’

It was this kind of thinking that caused the Germans in World War II to develop a hand-cranked 500 kHz rescue radio called the NS2. Nicknamed the "Notsender" for the letters in its designation, it was little more than an emergency transmitter that employed two crystal controlled vacuum tubes. Of interest, the design of the unit used a radio case that curved inward in the middle, so that a user seated in an inflatable life boat could hold it securely above their knees and between their legs, at which point they could then crank the attached generator handle to produce the power needed to cause the thing to transmit a May Day signal. In the case of the German NS2, a very basic Morse code distress signal was sent out when the handle was cranked.  

The British found an NS2 floating around somewhere near a German warship they sank, and being as inquisitive as ever picked it up and wondered what it was. Thinking that is was nothing important they didn't bother to tell anyone else about it but instead disassembled it to try and figure out what possible purpose it served. Fortunately, a little while later they found a second one and sent that one off to the U.S. Army Signal Corps. The Signal Corps immediately recognized it for what it was, and within a few months had copied the idea and released the SCR-578, the designation of which stood for not only the emergency transmitter itself, but all of the accoutrements that went along with it.

Issued mostly to the Signal Corps’ then controlled Army Air Force, the SCR-578 was meant to be carried on every aircraft that flew over-water, serving as an emergency transmitter in the event of a crash landing. The reality turned out to be otherwise however, as most combat fighter pilots tended to prefer to leave the thing behind and instead use the weight savings to carry additional rounds of ammunition instead.

Here’s where we come to the Gibson Girl part. Operationally, to assure that a downed pilot could use the device while still kicking at sharks, the unit was shaped like the German sibling it was copied from. It had an hourglass shape that allowed it to be held between the legs while it was cranked.

Army Air Corps combat pilots of the time being what they were… men… it was given the nickname the Gibson Girl… whether for its hour glass shape or the part about where it was held between the pilots legs and cranked, we don’t know. Either way, the name stuck.

To make sure the signal generated was transmitted as far as possible the unit was supplied with a metal framed box kite that was stored in a folded position but was unfolded for use. Once unfolded it was launched into the sky via a balloon, which in turn was inflated by means of a small hydrogen generator. The wire that linked the box kite and balloon to the unit served as the antenna. As in the earlier German version, power was provided by hand cranking.

The transmitter component of the SCR-578 was designated as the BC-778. Its frequency was 500 kHz, and it put out 4.8 watts. At that power level it had a range of about 200 miles (300 km). Unlike the German version which robotically sent out the signal as the crank was turned, the BC-778 made provisions for keying that could be either automatic (sending a standard SOS signal) or manual. At the time of its development and manufacture crystals were still a scarce item for the Signal Corps, and so, the SCR-578, not being high on the list of priority items to receive crystals, used tuning circuits.

Despite these limitations the SCR-578 saw long and reliable use, eventually finding its way into every branch of the U.S. military, and after the war into civilian use. It was not until much later that the Signal Corps released a post-World War II version that was called the AN/CRT-3. Only slightly modified from the original SCR-578, the AN/CRT-3 added a frequency in the 8 MHz range (to reduce the size of the quarter-wave antenna needed). It was designed for use by military personnel and civilians, in both ships and aircraft. A well designed and accepted piece of survival gear, the AN/CRT-3 saw usage up until the early 1970s.

The reader can readily understand that the SCR-578 and AN/CRT-3 were transmission devices. That is, they sent a signal out saying ‘come help me.’ But whether there was someone out there listening for this signal or not was not known. To complete the circle and make sure there were people tuned in to the distress frequencies the Signal Corps worked on developing a radio location device that could be mounted inside of an airplane specifically outfitted to perform the function of search and rescue.

This concept, when turned into reality, caused the development late in World War II of line-of-sight VHF radios. Centered around a much shorter wavelength, VHF allowed the use of simple dipole or whip antennas. The U.S. unit developed to serve this purpose appeared post WW II and was known as the AN/URC-4. It operated on the aircraft emergency frequencies of 121.5 and 243 MHz, which in turn involved wavelengths of 2.5 and 1.2 meters. At these wavelengths antenna lengths were ideally suited to the types of search and rescue aircraft then being used.[1]

As time moved on and the Vietnam era came to pass the Signal Corps did its best to stay on top of the task of keeping the survival radio systems it developed up to date, in terms of the latest in technology. Unfortunately post Vietnam budget issues constrained new radio development. The result was that while better designs could have been produced and brought to market post Vietnam they were set aside as part of the normal knee jerk reaction Uncle Sam has after a war is over... the one where Congress, acting in his name, cuts the budget for everyone and everything with the word military attached to it to the bone. In this case the effect was that better survival radio technological designs and circuitry sat on the drawing boards and failed to make it into the form of a finished product.

Yet while circuit improvements may have stood still during the early 70s, time itself was not standing still... nor were events. In 1972 Congressmen Thomas Hale Boggs, Sr. and Nick Begich,  flying on a light plane in Alaska, crashed and could not be found. Suddenly, Congress stood up and took notice of what the U.S. military, in the guise of the Signal Corps, had been saying for a number of years… that better survival radio technology was available, including designs for emergency beacons that self activated when a plane crashed. Just like that the law was changed, the budget was increased, and from that point forward our always responsive Federal Government began requiring that all aircraft carry an Emergency Locator Transmitter (ELT) that automatically activated in the event of a crash.

Initially, in order to get devices into the field quickly, the frequency used was left at 121.5 MHz (the standard emergency beacon frequency) so that existing equipment/transmitters could be used. As time wore on though newer devices began to reach the field, using 406.025 MHz. This frequency allowed the devices to be picked up by the Cospas-Sarsat international satellite system. Cospas-Sarsat was a satellite-based search and rescue (SAR) distress alert detection and information distribution system that was created by the U.S., partly in response to congressional mandates following the deaths of congressmen Boggs and Begich. Operationally, the system was jointly established by Canada, France, the United States, and the former Soviet Union. It’s first functional use was in 1979.

Based primarily on U.S. Signal Corps lab designs, the benefit of the 406 MHz beacon was that it allowed each transmitter to have a unique digital ID code. Anyone acquiring a device for use in their aircraft was required to register the code on the device, along with their contact details, with the Cospas-Sarsat authorities. In this way, even without anyone notifying the Cospas-Sarsat authorities that a plane was missing, when a signal was detected the digital ID code allowed Cospas-Sarsat to reach out to the people who registered the code and ask if everything was OK. Later, as time allowed for the introduction of even more sophisticated emergency beacon designs, newer models were introduced that could transmit location specific information derived from an internal GPS or GLONASS receiver.[2]

So successful was the Cospas-Sarsat system that over the years many countries joined the project, either as 'providers' of ground segments or as 'user states.' To date some 26 countries are providers of ground segments, while 11 countries are classified as user states. Today, Cospas-Sarsat, a concept that originated with the U.S. Army Signal Corps, is based in Montréal, Québec, Canada, eh.[3]

Maritime emergency beacon transmitters on the other hand have shifted from their early reliance on rescue radios that operated at the 500 kHz distress frequency to the Cospas-Sarsat system too. In fact the 500 kHz frequency is no longer officially monitored, although many ham radio operators around the world still keep a radio tuned to the frequency. To supplement the maritime environment’s unusual requirements for more than one means of transmitting emergency signals, radar transponders (which obviously respond to and transmit signals able to be seen by radar systems on other ships, versus radio systems) have been added to naval kits, as have hand-held marine VHF radios. The picture at right shows the SART Radar Transponder.[4]

In terms of where the U.S. Military is in regards to survival radios, military organizations now issue pilots and other combat personnel individual survival radios. Unlike the one-size fits all approach of the past, these radio systems have become increasingly sophisticated, with built-in Distance Measuring Equipment (DME), Global Positioning Satellite receivers and satellite communication. Looking back over all of the various survival radio sets/systems that the U. S. military has used and the Signal Corps has promulgated, one finds the following:

World War II

AN/CRC-7 - World War II era set, 140.58 MHz

AN/PRC-17

AN/PRC-32 - Navy rescue sets, 243 MHz

AN/PRC-49

AN/PRC-63 - Smallest set built

AN/URC-64 - (Air Force), 4 frequency rescue sets. Four crystal controlled channels (225-285 MHz)

AN/URC-68 - (Army), 4 frequency rescue sets

Vietnam War and Later Eras

AN/PRC-90 - Vietnam War era airman rescue set. The AN/PRC-90-1 and AN/PRC-90-2 are improved, repairable versions. They operate on 121.5, 243 and 282.8 MHz AM. The PRC-90 also included a beacon mode, and a tone generator to allow the sending of Morse Code.

AN/PRC-103 - (Air Force) Rescue Swimmer Radio.

AN/PRC-112 - Offered synthesized radio in the VHF and UHF aircraft bands. A PRC-112 and a hand held GPS were used by Capt. Scott O'Grady when he was rescued after being shot down over Bosnia. The AN/PRC-112B, initially known as the Hook 112, is a PRC-112 modified to include a GPS receiver, allowing encrypted position information to be sent. The unit also has a Cospas-Sarsat beacon. The latest model PRC-112G, built by General Dynamics can communicate with satellites. Over 31,000 radios in the PRC-112 family have been produced.

AN/PRC-125 (Navy) Rescue Swimmer Radio.

AN/PRC-149 Rescue Radio, replaced the PRC-90, PRC-112 and PRC-125 for non-combat use. It included both a GPS and Cospas-Sarsat beacon, and operated on 121.5 MHz, 243.0 MHz, 282.8 MHz, and 406.025 MHz. Built by Tadiran, the PRC-149 used standard D cell batteries, unlike other units that took special batteries.

AN/PRQ-7 Combat Survivor/Evader Locator (CSEL). This unit combines selective availability GPS, UHF line of sight and UHF satellite communications along with a Sarsat beacon. It can send predefined messages digitally along with the user's location. As of 2008, the PRQ-7 cost $7,000 each, “batteries not included.” A rechargeable lithium-ion battery pack cost $1,600, while a non-rechargeable lithium-manganese dioxide unit cost $,1520. As of October 2011 Boeing had delivered 50,000 PRQ-7s.

AN/URC-4 - 121.5 and 243 MHz.

AN/URC-11 - (243 MHz), "A" versions replaced one audio tube with transistors.

AN/URC-10 - The RT-10 are sub-miniaturized, completely transistorized UHF radio sets. They consist of a crystal-controlled receiver-transmitter, a 16-v dry cell battery, and a power cable assembly. The unit operates on one channel in the 240-260 MHz band (usually 243 MHz). RT-60 and RT-60B1 are two frequency versions of the RT-10. ·        

AN/URC-14 - (121.5 MHz)

With all of these systems out there, how can anyone feel all alone? If you’re that guy we started off talking about who was 69 years old and at home alone when his house was broken into at 0300, it’s now clear that all you needed to protect yourself was a good AN/PRQ-7 beside your bed.

And if you are that guy standing before a divorce court judge as your attorney resigns from your case, then what you need is a AN/URC-68 rescue set. Why? Because it will give you access to 4 different frequencies, and in your case letting as many people as possible know that you need help is the only thing that is going to save you at this stage of your life.

And as for you claiming to be the 18 year old at the rave party, forget about it. We all know you are far too old to be him. And besides, what any 18 year old needs to survive he already has: a cell phone and a Twitter account.

 

 

            

Footnotes

[1] On the Allies side, the VHF devices available for use during WWII included the British Walter, a small single vacuum tube oscillator design that operating at 177 MHz (1.7 meter wavelength). The Germans, pioneers in the use of VHF, used the Jäger (NS-4), a two-tube master oscillator power amplifier design that operated at 58.5 and 42 MHz. Both the British and the German versions were small enough to be carried in the life rafts that were found on single-seater fighter aircraft. - To return to your place in the text click here:

[2] GLONASS (Russian: ГЛОНАСС), acronym for Globalnayanavigatsionnaya sputnikovaya sistema or Global Navigation Satellite System; a space-based satellite navigation system operated by the Russian Aerospace Defence Forces. - To return to your place in the text click here:

[3] Ground Segments: Algeria, Argentina, Australia, Brazil, Chile, People's Republic of China, Greece, India, Indonesia, Italy, Japan, Republic of Korea, New Zealand, Nigeria, Norway, Pakistan, Peru, Saudi Arabia, Singapore, South Africa, Spain, Thailand, Turkey, United Arab Emirates, United Kingdom, Vietnam and two organizations, Chunghwa Telecom of Chinese Taipei and the Hong Kong Marine Department.  User States: Cyprus, Denmark, Finland, Germany, Madagascar, Netherlands, Poland, Serbia, Sweden, Switzerland, Tunisia  - To return to your place in the text click here:

[4] A Search and Rescue Transponder (SART) is a self-contained, waterproof radar transponder intended for emergency use at sea. The radar-SART is used to locate a survival craft or distressed vessel by creating a series of dots on a rescuing ship's radar display. A SART will only respond to a 9 GHz X-band (3 cm wavelength) radar. It will not be seen on S-band (10 cm) or other radar.  - To return to your place in the text click here:

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This page originally posted 1 December 2013