Torn. Fu. h


Translated from "Die deutschen Funknachrichtenanlagen bis 1945 - Band 2 "Der Zweite Weltkrieg" by Fritz Trenkle

The Torn.Fu.h was already in production by 1941/42 by direct order of the Wehrmacht ordinance office. This was the only transceiver where the control panel was on the broad side of the radio case, next to the battery. Likewise, the accessories like headphones, key, microphone, antenna sections, etc., fit into the side compartment and can be transported together. Dimensions were 36 cm x 35 cm x 20.5 cm, with the set weighing 14,5 kg. Both the receiver and transmitter shared the scale with a frequency range of 23,1 to 25,0 MHz which was represented by frequency numbers of 241 - 280 with 47,5 KHz intervals. The transmitter had two stages and is modulated by way of a push-pull stage that modulates the plate circuit of the power amplifier. The 5-tube heterodyne receiver has a common schematic with a self-oscillating mixer stage and a reverse feedback detector in the 2nd intermediate frequency amplification stage*. A built-in quartz crystal oscillator is provided for frequency testing, its third harmonic with the frequency of the transmitter's local oscillator on channel 249 provides a low beat frequency (tone). The construction of the Torn.Fu.h with 0,1 Watt power output includes the RV 2,4 P 700 tube in all ten circuits. The range of this transceiver is 1-2,5 km when using three or five antenna sections.

A more powerful version of this device was manufactured called the Torn.Fu.h a, with 1,5 Watts of output power with a range of approximately 4 km. In original documentation, it was deployed for "special purposes".

* Fine tuning of the local oscillator with the remote control is accomplished with the changing of the magnetic field of the spool through small electromagnets.

(MHz) 23,1 - 25 MHz.



Sectional rod




One storage battery of type 2.4 NC 28 and a built-in vibrator unit WG1 2.4a. Battery capacity at a temperature above 0 Centigrade is about 15 hours, one-third of the time transmitting and two-thirds of the time receiving.

Torn.Fu.h a



Transmitter: 4 x RV 2,4 P 700

Receiver: 5 x RV 2,4 P 700

Used by Wehrmacht Heer (infantry) to communicate with Sturmgeschütz self-propelled howitzers which provided light artillery support for the troops.


1-2,5 km

Ukw.E.h / 10W.S.h - (Fu 16)





Obverse of the set.



Lid closed. the lid is made from very thin metal.



Battery compartment, accessory storage and power switch.



1942-dated set with a rather low serial number.



Voltmeter, and antenna current meter. The red button activates the filament voltage measurement, while the blue button measures the antenna current.



Detachable remote control.



Top surface of the remote control showing the microphone and headphone connectors.



Antenna base attachment at the top of the unit.



Inside of the front cover showing the mounted antenna sections.



Close up of the antenna sections, and the very rare first section with the loading coil. That section and the one next to it are marked with a red stripe, while the other two are marked with light blue stripes. The purpose of this marking is unknown. The operating instructions state, when using all five sections, place the spool section in 3rd position, and when using just three sections, place the spool first on top of the antenna base. With three sections, the range is advertised as around 1 km, and with all five sections, the range is at around 2,5 km.



Internals of the transceiver with the cover removed



Internals of the transceiver with the cover removed



Torn.Fu.h from the top. Note the antenna coupling connector next to the big screw.



Close up of the tuning capacitor block and ball-bearing.



Left side of the transceiver. Most of it is in very good condition



Waffenamt 444













A.  Subject and Frequency Range

The Torn.Fu.h is a portable transceiver with power configurations to support the following modes:

  • Transmission: Voice
  • Reception: Voice
The device operates as a one-channel transceiver.  This means the receiver and transmitter operate on the same frequency and are controlled by a knob.   The device is calibrated in the following channels:

  • Frequency numbers: 241 to 280 (40 Channels)
  • Size of each channel on the scale:  50 KHz
  • Frequency range:  24,95 - 23 MHz (12 - 13m)
  • Inventory tag:  Torn.Fu.h

B.  Technical Construction

The transceiver, frequency tester, power supply are encased in a moisture and dust proof container which also has a box for the battery and other accessories.
On top of this container is a socket for the antenna foot.  On the inside of the lid, there are 5 stackable antenna sections.

The following items on the front control panel are listed in order (see diagrams 1 and 4):

  • Meter (with 3 parameters) ............................................33
    • Antenna current when the transmitter is used
    • Filament voltage when the red button is pressed
    • Anode voltage when the blue button is pressed
  • Knob "Ant. Abst." (antenna tuning)................................30
  • Frequency scale ..........................................................a
  • Knob - frequency setting...............................................6,43,62
  • Locking knob for frequency setting.................................b
  • Headphone jack for testing transmitter...........................115
  • Headphone jack for testing receiver...............................116
  • Connection guides for remote control "a".......................c
  • Connection socket for remote control "a" and cable "a"...d
  • on/off switch................................................................142
  • On remote control a: feedback adjustment knob.............106
  • On remote control a: fine frequency adjustment knob......107

II.   Current Sources

The sources of power to operate this device are derived from inside the container.  Filament voltage is 2,4 volts and anode voltage is 100 volts.   Both the microphone and relay operate from 2,4 volts.

The following are provided as current sources:

  1. A 2,4 Volt accumulator (2,4 NC 28)
  2. A vibrating power converter 2,4 a for the anode and screen grid voltages which runs off the 2,4 volt accumulator.

III.  Internal construction

Illustration 2 shows the reverse of the transceiver with the case removed.
  • Transmitter section             a
  • Receiver section                 b
  • Power converter section      c
  • Frequency test section       d

1.  Simplified schematic of

a) Transmitter (diagram 5)

The master oscillator stage generates high-frequency oscillations through a reverse feedback circuit.  These oscillations move through the oscillator tube 12 and combine with the tuning block of the transmitter which is comprised of spool 1, variable capacitor 6, and fixed capacitors 5 and 8.  The reverse feedback voltage is taken from capacitor 8 and fed back to the control grid of tube 12.

The anode voltage of tube 12 is passed through resistor 15 and drossel 13. This serves to block the anode voltage source from the HF alternating voltage.   The anode voltage is also delivered to the screen grid.   Capacitor 14 sends the high frequency voltage to ground.   The bias voltage results because of the voltage drop of the control grid current across resistors 9 and 10, which flows from the control grid to the lower section of spool 1.

Final stage

   The final stage amplifies the high frequency oscillations with the help of tube 17.   The Output circuit consists of the HF transformer 39 and variable capacitor 30 (Ant. Abst.).
   The antenna is appropriately coupled, so that it's tuned for the middle frequency.  Because of the small frequency range the top and bottom of the frequency range are tuned exactly.
   The oscillations of the transmitter are transferred to the rod antenna through connector A (Buchse A).   During operation, the voltage that passes through the antenna can be measured by the antenna current meter 33.
   The anode and screen grid voltages are taken from the secondary winding of transformer 19 which takes power from the anode voltage source.   Capacitor 18 channels the high frequency voltage of the screen grid to ground.   The bias voltage drops across resistors 9 and 10 before it reaches the oscillator tube 12.
   The anode voltage passes through the secondary winding of transformer 19.   To overlay The LF voltage with the DC voltage, the LF voltage passes through the primary winding, which is transformed with the DC voltage which is passed through the secondary winding.  Then the HF oscillations are either attenuated or amplified in rhythm with the LF oscillations in the output stage, and are modulated by the LF oscillations.

Modulation circuit

   The low frequencies generated from the microphone voltage oscillations pass over the modulation transformer 28 to the control grids of tubes 20 and 24 which are in a push-pull configuration.   After their amplification they are overlaid on transformer 19 of the anode DC voltage of the final stage amplification tube.   The primary winding of transformer 19 and capacitors 21 to 25 comprise the low-frequency oscillating circuit, which is closed using capacitor 141.  In this way, an identically measured amplification of the mid-range speech frequencies is attained (300...3000 Hz).
   The anode voltage of both modulating tubes is driven through the middle-tapped primary winding of transformer 19.   The screen grid voltage is taken from resistor 23 of the anode voltage source; capacitor 22 channels low frequencies to ground.  The control grid voltage is taken from resistor 10 and is driven toward the control grid through resistors 11, 26 and 27 respectively.

b)  Receiver (Diagram 6)

Pre-selector stage

   High-frequency oscillations come from the antenna to the pre-selector stage, which consists from the secondary winding of transformer 29 and variable capacitor 30 (this pre-selector is tuned in synchronously with the output stage of the transmitter).

High-frequency amplification stage

  The high-frequency oscillations are driven towards the control grid of tube 36, in which they are amplified and sent towards the the tuned anode circuit.   This consists of spool 40, variable capacitor 43 and fixed capacitor 47.  The anode voltage for tube 36 is driven through spool 40, and voltage for the screen grid is driven over resistor 38.   Capacitor 37 removes unwanted HF oscillations to ground.  Resistor 35 is shunted across the high-frequency capacitor 34, and operates as grid leak resistor.

Mixer and Heterodyne Stage

   This stage has two tasks to perform.  First, local oscillations are generated through a reverse feedback arrangement.  Additionally, the local oscillations are overlaid onto the received HF oscillations in tube 51, whereby the fixed intermediate frequency is created.
   The local oscillations result from tube 51 working together with its resonant circuit.   The resonant circuit is comprised from spool 57 and variable capacitor 62, both of which are bound together with the anode of tube 51 over capacitor 56.  The reverse feedback voltage is taken from the tap of spool 57 and is driven over the filament wire of the directly-heated cathode.   Choke 45 stops the channeling of HF to ground.   Received signal frequency is applied to tube 51 over capacitor 49, so that both the received frequency and the generated heterodyne frequency are delivered to the tube.   In tube 51, both frequencies are combined to create a new frequency - the intermediate frequency (IF).   This IF travels to the next stage over choke 55.   This choke blocks HF oscillations from entering the IF stage.
   The anode voltage is transferred over spool 65 and choke 55, and the screen grid is connected to the anode voltage source through resistor 53.  Capacitor 52 directs unwanted high frequency oscillations to ground.   Bias voltage reduction is accomplished with resistor 50 for the control grid.

Intermediate Frequency Amplifier Stage

   The intermediate frequency oscillations transfer to the IF- bandwidth filter, wich consists of two circuits that are coupled with coupling capacitor 69.  The factory-tuned circuits are comprised of spool 65 with 70 and capacitors 66 with 71 together.  These oscillations are amplified in the IF tube 75, and transferred to the control grid circuit of the detector.
   The anode voltage source provides the anode voltage over spool 78, while the screen grid voltage is delivered over resistor 77.   Capacitor 76 directs unwanted oscillations to ground.

Detector Stage

   The control grid circuit of the detector stage is comprised of spool 78 together with capacitor 79.  This circuit is connected over capacitor 82 to the control grid of the detector tube 85.   During reception, the modulated IF  signal is rectified, and the LF signal is produced in this tube, which corresponds with the original transmission.
   The feedback voltage is induced over capacitor 84 through the lower part of spool 78 to the control grid circuit.   This stage also achieves volume control with the knob "Feedback" of the potentiometer 106.   The potentiometer 106 changes the screen grid voltage of the detector tube, thereby the amplification, which allows volume control.  The amplification can be so increased, that the detector stage can start to oscillate.  In this case, a telegraphy transmitter cannot be received.
   The anode voltage comes from the anode voltage source over resistor 92.  The screen grid voltage is transferred through an adjustable voltage divider 89/90/106.   The control grid bias voltage is delivered onto resistor 83, which is connected to the positive filament lead.   Capacitor 80 leads the IF back through the cathode.  Capacitor 88 directs unwanted ZF oscillations to ground.

Low Frequency Amplifier Stage

   The low frequency signal is taken from resistor 92 and is transferred to the control grid of the LF tube 99 over capacitor 94.   The amplified oscillations pass over transformer 102 and capacitor 103 to the headphones.
   The anode voltage is taken from transformer 102, while the screen grid voltage uses the anode voltage source which is passed through resistor 101.   Capacitor 100 directs low LF oscillations to ground, and capacitor 103 keeps DC voltages away from the headphones.  ????The bias voltage transfers to resistor 95 and capacitor 98, through wich the IF is bridged. ?????

2.  Schematic
   a) Transmitter (Diagrams 7 and 11)
   In the tuned circuit of the generator stage there are additional fixed capacitors 2 ,3 ,7, 8a and trimmers 4 and 7a.   These are constructed from various different materials and compensate for temperature changes which prevents frequency deviation, and serve for balancing the circuit.
   In the final stage and respectively pre-selector stage, capacitor 31 is parallel to the tuning circuit.  One part of the HF voltage is passed through instrument 33 through rectifier 32 and resistor 32a, so that the meter deflects during transmitter operation.  Capacitor 41 serves to conduct the remaining HF signal.  When the microphone switch is activated, potential 4 is connected to ground. The winding of relay 117 is energized, binding potentials 1 and 6 and thus maintaining the filament voltage of the transmitting tubes.
   For the anode-, screen grid-, control grid- and filament circuits, see diagram III 3, and the device schematic (diagram 11).

  b) Receiver (diagram 8)

   The capacitors 42, 44, 44a 45 and 63 individually determine the frequency range of the anode circuit in the HF amplification stage.  A similar purpose is served by capacitors 60, 61, 63a, 58, and 59 for the oscillator circuit in the heterodyne.   The frequency range of this circuit is chosen so that it maintains the same frequency difference from the other circuits, and tuned synchronously with them.
   Additional tuning of the heterodyne circuit can be performed through the changing of the magnetizing-current level of the Pre-magnetizing-control hole 64 with regulator 107 which is the fine-frequency control.  While changing the pre-magnetization of spool 64, which is located in the tuned heterodyne circuit, leave the frequency within the specific boundaries.
   In the detector stage, there is a filter chain for the remaining IF residual voltages, which is comprised from resistor 86 and capacitor 87.  The same task is performed in the LF stage's filter chain, which is comprised of resistor 97 and capacitor 98.
   For the anode, screen grid, control grid and filament circuits, refer to the complete schematic (Diagram 11).

  c) AC Rectifier 2,4 a  (diagram 9)

   The transceiver requires a filament voltage of 2,4 volts and an anode voltage of 100 volts to operate.  Filament voltage is delivered from the 2,4 NC 28 battery, while the anode voltage is taken from the AC rectifier, which operates from the 2,4 NC 28 battery.
  The operation of the AC rectifier is described as follows:

   After switching on the device, the battery current flows through switch 142, choke 123, and to the middle tap of the first winding of transformer 125, to potential 83, to contact B, and then over potential 85 and choke 123 to (-) ground.  Simultaneously, the current flows over potential 82 to the magnetic winding of the AC rectifier, and further over potential 86 through the contact B and finally over potential 85 and choke 123 to ground.  As soon as the current flows through the magnetized winding of potential 86, the mechanically coupled contacts A and B are pulled over to the left.  Here, potential 85 is connected to potential 84, and is separated from potentials 83 and 86.   The path of the current switches from potential 83 and is connected to potential 84, so that the current in transformer 125 from the middle-tap flows through potential 84 and not potential 83.  Simultaneously, as there is no current in the magnetic winding, both of the contact tumblers A and B are mechanically returned to their starting position by the spring tension.  Then this process repeats, so that also in the primary winding of transformer 125, the current flows alternatively from potential 82 to potential 83 and to potential 84.
   In this way, AC is induced in the secondary winding of transformer 125, in conjunction with the alternation of the contact tumbler A of the rectifier 118, the following currents are induced.  In a  resting state, the contact tumbler A allows a positive current to flow from the middle position potential 77 over additional filters to potential 2, then the transceiver, then to ground (potential 0) and back to contact tumbler A (potential 0), contact for potential 78 and further to the secondary winding of transformer 125.   When contact A is engaged (activated), the following current path takes place:  To potential 2, through the transceiver, through contact 79, through transformer 125.  As a result we also obtain the same current direction in the transceiver.   This rectified current is further smoothed by the filter circuit.  The latter consists of chokes 133 and 135, and also capacitors 130,132,134, and 136.   The capacitors 126, 127 and 131 are connected in parallel with the spark gaps of the AC rectifier system to avoid sparking.
   In the current circuit of the primary winding of transformer 125, the following low frequency and high frequency interference reduction takes place:
Double-choke 123, capacitors 124, 129, 128.   The capacitors 119, 120, and 121 are also connected in parallel to the spark gaps.
   The interference reducer for the filament voltage is likewise located in the rectifier device, and consists of choke 139 and capacitor 138. 

d)  Frequency tester (image 10)

   The tuning of the frequency range of the transmitter and receiver is achieved by the built-in frequency tester.

Tuning the frequency of the transmitter

For frequency testing of the transmitter insert the headphone plug into both small holes of the left turnable disk 115 marked "Frequenzprufen S" until the plug is flush with the surface and turn the disk clockwise. Then rotate the headphone plug against the faceplate and sandwitch the open sockets under the rotating disk. Through this rotation the filament voltage for Tube 110 is connected to the frequency tester, and the realy coil 117 is connected to ground. Thereby, the armature of the relay is energized, so that the heating of the transmission tubes is also turned on.
Onto the control grid of tube 110 lays simultaneously over the coupling capacitor 72 the oscillations of the exciter stage and the oscillations of quartz crystal 108. Resistor 109 serves as the grid leak resistor. In tube 110, harmonics are generated from the quartz oscillations, which are mixed with the oscillations from the exciter stage. This creates the third harmonic of the quartz (23,4 MHz) with the oscillator frequency with the frequency number 249 the heterodyning, a tone becomes audible in the headphones. The anode circuit, composed of spool 111 as well as capacitors 112 and 113, is on the own frequency of quartz 108 tuned. While the audible low-frequency oscillations are passed over the secondary winding of the transformer 114 to the headphone connectors 115, all high frequency oscillations are sent to ground over capacitor 114a.

Tuning the receiver

In this situation, connected the headphone plug into both small openings in the right-hand rotatable disk 116 marked "Frequenzprufen E", and rotate the disk clockwise until the plug is in horizontal position. Then push the plug into the front panel until the rotating disk is sandwitched between the plug and the faceplate. This rotation connects the filament voltage of vacuum tube 110.
The vacuum tube 110 performs the frequency testing function by operating as a quartz-controlled transmitter (which energizes both the fundamental frequency and harmonics as well). The oscillations flow through capacitively coupled paths in the receiver, the same way the received frrequency does. The third harmonic of the quartz combines with the heterodyne of the receiver to produce a low-frequency, audible frequency, so long as he tuning knob is set to the frequency number 249. With the (energized) reverse feedback, a tone is heard through the headphones.

3. Complete schematic (Diagram 11)

In the complete schematic shows the combined operation of the transmitter, receiver, frequency tester, and power supply. The numbers in circles show the component numbers, while the numbers without circles show the circuits.

Filament circuits

The positive accumulator voltage passes over the On/Off switch (142) to the rectifier, (here one side of the energy of the anode DC operates and flows to other as potential 1 (+H) to the rectifier). The negative pole of the accumulator is connected directly to ground. When the reeciver is operating (speaking key is open), the filament voltage passes to all of the vacuum tubes of the receiver. While the (speaking key) is closed, potential 4 is connected with potential 0, the winding of relay 117 voltage and contact potential 1 is with contact of potential 6 connected, so that the transmitter vacuum tubes are heated. The heating of the receiver is activated with a closed (speaking key). Also: only by a closed (speaking key) does the transmitter oscillate. With an open (speaking key) the receiver operates.
In the filament current circuit the heterodyne vacuum tube 51 is a HF choke 54 is connected. Capacitors 16 and 39 work as blocking capacitors for the high frequency to ground. Capacitors 16 and 39 are bypass capacitors that send unwanted high frequency to ground. The filament voltage source delivers the microphone resting voltage and over the adjustable resistor 107 the direct current for the various bias of spool 64, with the fine tuning of the receiver made.
With the pressing of the red button on the meter 33 one can observe the filament voltage.

Anode circuits

The rectified anode voltage is taken from the secondary winding of transformer 125 and is sent to potential 77. The oscillator tube 12 of the transmitter receives the anode voltage over choke 13 and resistor 15. Tube 17 receives anode voltage through the primary winding of transformer 29 and the secondary winding of transformer 19. The anode voltage for tubes 20 and 24 of the modulation circuit is also taken from the primary winding of transformer 19. In the receiver, the various tubes take their anode voltage over the series resistors 48, 68, 81 and 105. Capacitors 67 and 80 conduct HF and respectively ZF to ground. Capacitor 104 provides the feedback for NF. The vacuum tube 110 of the frequency tester takes its anode and suppressor grid voltages from resistor 73, the primary winding of transformer 114 and spool 111. With the pressing of the blie button on the volt-meter 33, the anode voltage can be measured.