nofars.net

GIBSON GIRL 
By Billy Williams, N4UF

In the 1980s,  NOFARS member Ed Harvey, K4YNM gave me a military surplus AN/CRT-3 Radio Set.  In mint condition, it was a "Gibson Girl." Ed joined NOFARS in the early days.  Ed is now deceased.  His son-in-law is Randy Bahr, KI4RHQ, now NOFARS President in 2014.

I brought the Gibson Girl to a NOFARS Show & Tell Night. We got a chance to look inside and it generated curiosity.

I taught electronics at the FCCJ Geis Marine Center when Ed gave it to me and the Gibson Girl was very useful as a teaching prop for demonstrating principles of generating electrical power.

Turning the crank produced enough power for a light bulb and also for a transmitter that generated an automated SOS on 500 Hz and 8280 Hertz.

The Gibson Girl package included a box kite, two balloons and a canister of hydrogen gas. When combined with water, the hydrogen would fill up the balloons in case the wind wasn't blowing.

A 300 foot antenna wire reeled out of the main unit and attached to either the balloon or box kite. A ground electrode attached to another wire was thrown overboard.

According to the instruction book, the AN/CRT-3 was a simple, rugged emergency transmitting system carried on aircraft and designed for operation from a rubber life raft. The set was dropped over water using a parachute. Radio transmission on two frequencies was intended for reception on 8280 KHz by stations cooperating in long distance rescue and on 500 KHz by aircraft and ships participating locally in a rescue.

The AN/CRT-3 was sufficiently buoyant to float and was colored brilliant orange-yellow to give good visibility. The radio transmitted automatically in code. Provision also was made to allow manual keying using a push button.

In addition to transmitting RF, the radio set also supplied power for a signal lamp (M-308-B). All electrical power for operating the radio and/or signal light was furnished by the hand-powered generator inside the transmitter cabinet.

RF power output was about 2 watts on 500 Hertz and 2 1/2 watts on 8280 KHz. The instructions indicate that possible ranges were up to 300 miles on 500 KHz. and 1500 miles on 8280 KHz. 

Including the generator/transmitter, kite, hydrogen generator, accessories and equipment bag, the Gibson Girl weighs about 36 pounds. A parachute also could be included and it weighed an additional 4 pounds. Typically, if a plane was about to crash or be ditched, the rubber life rafts and Gibson Girl were thrown out just before the crew bailed. Crew members then would swim to the rubber life rafts and Gibson Girl.

The Gibson Girl also could be dropped from a rescue airplane to assist survivors during a rescue operation. Extra padding was available to drop it over land.

The concept was developed by the Germans during early phases of World War II. The U.S. improved upon the German invention and produced the Gibson Girl later in the war. It was used extensively during the Korean War but was replaced by much smaller devices operating on VHF, such as the EPIRB, in the 1970s.

The two tube layout includes a 12SC7 as an audio modulator (the unit sent modulated CW to aid in reception) and a 12A6 as an RF oscillator/output. A rotating wheel automatically produced SOS when the generator was turned and keyed either the light and/or the transmitter.

The unit was shaped to fit between the legs of an operator sitting on a life raft. It was important to turn the generator at a constant speed and an additional pilot lamp was included in the unit to help the operator keep the proper cranking speed. The term "Gibson Girl" came from the shape of the unit.

The next time you watch an old war movie, look for a Gibson Girl whenever a plane crashes or life rafts are in use.