German Five-Watt Sender, WWII Tactical and Technical Trends, No. 45, April 1, 1944 (Lone Sentry)

The German five-watt sender, "5W.S./24b-104," is a medium frequency transmitter which is used in divisional and regimental nets of the German army both as a ground and as a mobile station. Its operation is very simple and it could readily be put into emergency use by our troops. However, its frequency band is below that of our sets of comparable transmission range. It does fall within the frequency bands of the SCR-177, SCR-188, SCR-193, SCR-245, SCR-299, SCR-506 and SCR-543 and could be netted with these sets. For operation as a ground station it is supplied with a foot-pedal generator, and for vehicular use it operates from the vehicle storage batteries through a dynamotor.

a. Technical Data

(1) Frequency range,

In four bands:   I   950 - 1,500 kc
                II   1,450 - 2,050 kc
               III   2,000 - 2,600 kc
                IV   2,500 - 3,150 kc

(2) Preset frequencies -- Two. Shifting by means of a mechanical method.

(3) Tuning -- M.O (modulated oscillator).

(4) Power supply -- Pedal generator, automobile storage battery and dynamotor, or gasoline motor generator, depending on unit to which it is issued.

(5) Power consumption

Filaments - 1.3 amp at 3.8 volt -- 5 watts.
Plates - 0.14 amp at 300 volt -- 42 watts.

(6) Power output, telegraphy -- 5-7 watts.

(7) Antenna -- Standard antennas: (1) horizontal wire and counterpoise of 15 meters; (2) automobile roof-antenna; or any of the following may be used: (1) high antenna (10-meter mast with 15-meter horizontal wire and 25-meter counterpoise); (2) ground antenna (2 ground cables of 25 meters each, rolled out to 5-12 meters); (3) emergency antenna of uncoated wire or field cable 10-30 meters long and counterpoise cable of 15-20 meters.

(8) Tubes -- 2 - Telefunken Type RS 241

b. Military Characteristics

Range, with horizontal antenna: telephony, 10 miles; telegraphy, 35 miles.

Dimensions, without fittings -- 17 in high, 13 in wide, 8 in deep

Weight, excluding all accessories -- 46 lbs

Transportation -- Transported or mounted in vehicle; also carried by one man as a back-pack.

c. Physical Characteristics

The transmitter is carried in a metal case which is provided with a carrying handle on top, hooks and rings at the rear for attachment of a harness, and wooden foot rests on the bottom. The case is a light metallic alloy material, reinforced by sheet iron strapping. It is of very heavy construction and weighs almost as much as the transmitter itself. The front cover, which is fastened on with four tension clamps, is fitted with rubber stripping to make the set waterproof when closed for transportation. This case contains no accessories.

d. Transmitter

(1) The transmitter can be removed from the case by loosening the four screws encircled in red. The operating panel and a portion of the mountings on its rear are cast as a single piece of light alloy. The panel and all mountings are painted gray.

An attempt has been made to make the construction as stable as possible in order to retain electrical stability during vehicular operation. The plate on which the tubes are mounted is bedded in cotton felt to reduce vibration of the tubes. The tubes are clamped into holders.

The operating instruments include a voltmeter for plate and filament voltages and an ammeter in the antenna circuit. The dialing mechanism, while of sturdy and positive construction, is of old design. Two frequencies within the entire tuning range may be preset by the clamps which are located on the large ring on the operating panel. This ring serves as a friction drive for the tuning knob, and setting the clamps limits tuning to frequencies between the two preset values. The four bands are color coded for both the band switching and tuning dials. The large radius of the tuning dial makes unnecessary the use of a vernier scale and the scales are directly calibrated in kilocycles.

(2) Repairs and replacement of faulty sections are simplified by block construction. The components are considerably spread out. There are no soldered electrical connections between sections, all conductors going either through multiple plugs or through terminal strips employing screw-on connecting lugs. Wires are color coded and all terminals and components are numbered.

e. Electrical Characteristics

The transmitter consists of a simple master oscillator power-amplifier, using a type RS 241 triode in each stage. The main bandswitch controls the switching taps in the oscillator, plate, and antenna circuits. The oscillator and plate tuning circuits are ganged to simplify operation. Required input voltages are 4-6 volts for the filaments and about 330 volts for the plates.

In telegraphic operation, the plate circuits of both tubes are keyed. Condenser 48 and resistor 49 function as a key filter (numbers correspond to those found in set).

In telephonic operation the grid of the power amplifier is modulated, the audio voltage being amplified only by the microphone transformer. In order to reduce the average plate current to the proper value for telephone operation, resistor 46 is switched in, in place of resistor 25; this increases the bias on the final amplifier tube and results in a decrease of about 30 per cent in the antenna current reading.

The filament input voltage can be somewhat in excess of the required 3.8 volts since it can be controlled by the rheostat in the filament circuit. Condenser 17 and resistors 22a and 22b provide an r.f. return to the electrical center of the cathodes, thus eliminating the possibility of modulation by low-frequency variations which might be present in the power supply.

f. Operational

Preliminary

(1) Turn main switch to the "Aus" off position.

(2) Connect antenna, counterpoise, and "Empf.-Ant" - receiving antenna - to the antenna terminal of the receiver.

(3) Plug power supply into the receptacle and connect key.

(4) Turn filament rheostat to extreme left.

Tuning the Transmitter

(1) Select band and frequency desired. If operating in a moving vehicle, clamp the tuning knob in this position.

(2) Turn main switch to "Tgr" - telegraphy (CW).

(3) Turn on the power supply.

(4) Advance rheostat until the voltage reads 3.8 volts.

(5) Press telegraph key and voltmeter button. The voltage should be within the blue sector of the scale (300-330).

(6) Adjust antenna coupling "Ant-Fein" - antenna tuning for maximum output as indicated on the ammeter. If maximum current goes beyond the scale, it will be necessary to complete this tuning in the "Tfn" position.

(7) Preset one or two frequencies, as required. It is always necessary to readjust the antenna coupling after a frequency has been changed.

Telephony

(1) For telephonic operation, connect microphone switch and proceed as above, in the "Tfn" rather than in the "Tgr" operating position.

(2) To check for modulation, speak into the microphone. The ammeter needle should vary, indicating the presence of modulation.

Reception

(1) A receiver of the type Tornister Eb is ordinarily used with this set.

(2) For reception, turn the operating switch to the position "Empf". This switches the transmitter antenna from the transmitter to the "Empf. - Ant." binding post which is connected to the receiver.