The unit is capsuled in a "press-stoff" (backelite) case.On top it is 2 pieces of carabin-lock-rings and underside 2 flat snap-on ring hooks.This is the basic connections for the backpack leather-belts.On the top you see the antenna connections,where the antenna is 73cm long and marked RED for b model (100Mhz).Model c is green. (130Mhz). Included is 1 battery 2.4v 28A and telefon unit (there is 4 differents types) 1 controll head (Volum and Frequenc adjust). 2 headphones.
Accumulatoren 2.4v-dc, 28a and a vibrator power deliver the highvoltage power to the valves. ( ca 128-130v dc). From the front-top of Tornister Feld.Fu.b you have the channel selector,starting frequence 90.575 to 110.575Mhz splittet in 715kc channel seperations. Turning a little down,we have the controll unit. Here it is possible to adjust volume and frequence,and under this on right side you see the connections to headphones and the microfon with push and talk. The microfon is a carbon type. On the left hand it is a controll window with a gas-valve.If the voltage is over 120v is lights clear,a control of the battery power. At the end, On Off switch. Realy simpel and work after 60 years. Inside after taken the unit out of the house,we start with the princip of working. The unit working together as a transmitter and a receiver (superegenerative) a metod where the valve oscillating ( RL2.4T1) with very low anode voltage ca 35-40v.In front of this it is a RF amplifier (RV2.4P700) that helping to get a better signal noise ratio,and blocking the RF sqeesing from oscillator to reach the antenne and blocking nearby radio sets. The signal going from the anode of oscillator through a transformer to the AF amplifier input (RL2.4P2) amplified and transformed to the headset output. Then the transmitter work right the other way. From the mik input,2.4 volt going through the carbon microfon-element an produced a signal going to the transformer and inducted to AF amplifier RL2.4P2 where the signal going modulated (AM) through the modulator transformer to anode on transmitter valve,This valve RL2.4T1 will oscillate normally with anode voltage on 130v and giving ca 150mw power output.As power,this time they working with syncron-vibrators. It means it have a second contact set (secondary) on the highvoltage restifying the voltage to DC from AC.(Later this restifying was made of diodes,1947 and later). So here we are through the princip of the Tornister Feld.FU.b (b1 and c). This unit was constructed mainly for "Flak" Big canons as 88 mm and so,communications and this type of receiver/transmitter was very functionally for this purposes. Later all type of military equipment was superhetrodyne receivers,this type has a smaller band covering and do not make squieesing from the unit. Ordinarey military band stay around 21-54 Mhz.
Russian R-105D series
RA-105 (PRC-10a) (Swedish)