Lone Sentry: New German Emergency Transmitter (WWII Tactical and Technical Trends, No. 39, December 2, 1943)

The German Emergency Transmitter NS-4 is a 2-tube, self-contained, battery-operated, air sea rescue transmitter, apparently replacing the NS-2 prototype of the Gibson girl transmitter. The apparatus is colored bright yellow, is buoyant and water-tight, and a length of cord and a hook enable the instrument to be secured to a person or small boat.

The estimated life of the battery on intermittent use is about 4 hours. The instrument is preset in the frequency band of 53.5 to 61.0 megacycles and radiates a modified continuous wave note of approximately 400 c.p.s.*

The equipment is well-designed, its special features being its compactness and light weight. It has a limited life however, and gives evidence that it was designed to replace the NS-2 which uses far more critical materials.

a. Construction

The equipment is housed in an aluminum box measuring 6 1/4 x 6 1/4 x 3" and weighs 3.5 pounds. The base and lid of the box are stiffened by 2 ribs made diagonally in the material and the lid is secured by 4 screw fittings which are rivetted on the outside of the box. A rubber gasket ensures a watertight joint.

The transmitter is secured in the box by means of 4 captive screws, one of which is used as a connector to the aerial. Two of the screws are located beneath the batteries which must be removed before the screws can be loosened.

The chassis is not of the usual die cast construction but is of sheet aluminum spot-welded together. No tube holders are used, the connection being made by soldering directly to the pins of the valves. The coils and condensers are of ceramic material with the exception of paper smoothing condensers in the vibrator pack.

[German Emergency Transmitter WWII]

b. Antenna

The antenna is of particular interest. It is a 3 ft 5 in strip of copper-plated steel tape similar to that used in pocket rules, and is wound around the box when not in use.

The antenna system might be used on vehicles or pack sets but would not be suitable for aircraft use. The base of the antenna is 1 inch tapering to 3/16 inch and has been sheathed in rubber for the last 10 inches to avoid shorting due to heavy rain or spray.

The antenna may be swivelled in one plane and is wrapped round the instrument and held in position by 2 clips when not in use.

Two press switches fitted with rubber covers are located under one of the antenna retaining clips; when the antenna is unwound the transmitter is automatically switched on. In the sample examined one press stud marked K was not used, the contacts of the switch not being fitted. This is probably used to key the transmitter for sending Morse and conserve the battery life.

c. Vibrator Unit

The vibrator is of the non-synchronous variety and is particularly interesting as the frequency is approximately 210 c.p.s. The armature is of unusual design being a light, flat strip at right angles to the reed. The magnetic circuit is smaller than in the conventional vibrator although the driving coil is a good deal larger. A separate driving contact is used and the whole contact assembly is considerably smaller than usual.

No rectifier is used, the raw A.C. being applied to the transmitter so that the carrier will be modulated at the frequency of the vibrator and its harmonics.

d. Batteries

The 2-volt lead acid batteries used for power supplies are 1 1/4 x 1/2 x 1 3/4" and weigh approximately 1 1/2 ounces each. Eleven are used in all, 3 in parallel for the 2-volt filament supply and 8 in series parallel for the 8 volt vibrator supplies. These make up 1 pound of the 3 1/2 pounds which is the total weight of the equipment. These batteries were originally developed for the meteorological balloon transmitters.

A discharge test was carried out and the 2 volts fell to 1.7 volts in 2 hours 40 minutes and the 8 volt to 6 volts in the same time. A translated enemy document indicated that the batteries last 4 hours if switched on for 3 minutes and off for 1 minute.

*Cycles per second