Patrouillenfunkgerät SE-106 / P5F Set or P5 Flieger Set; developed and produced by Zellweger AG, Uster.
The P5 set constructed by Zellweger, Uster, is the high power variant of the „P Geraet“, the patrol radio set. In 1944, when also the Air Force and Anti aircraft units needed replacement for their wireless equipment, the necessary valves to produce another batch of the SE-105 were not available. So Zellweger adapted the set to accumulator operation (to get away from expensive special batteries) and to the tubes that were still available in an early moment of the production run (in fact early P5F can be found with the tubes found in standard P5.
The station is equipped with a NiFe accumulator. This can be used for reception and is loaded with the hand cranked generator. For transmitting, the generator always has to be cranked as higher plate voltage power is necessary. When the main switch of the transceiver is in the 0 position, only the complete power coming from the generator is used to recharge the accumulator.
The P5F set (Patrol Set 5 Watts Air Force) consists of a transceiver case with the transceiver in the upper part and an inverter and accumulator in the bottom compartment, a generator case (another 15,4 kg) with the hand cranked generator and spares and a canvas bag (5,7 kg) with material for a long distance antenna.
In the transceiver case, the transmitter section is located at the right and the receiver section at the left side.
The receiver can be powered from the accumulator and the inverter for HT and / or the hand cranked generator; for transmitting, the hand cranked generator must be used under all circumstances, a relay prevents the transmitter section to be be powered from the battery which might be exhausted very soon.
The set switches automatically from receive to transmit mode when the push-to-talk button is pressed or when the morse key is operated, one second after transmitting the last morse code letter, the SE-106 returns to receive operation.
The operation of the transceiver is easier then to supply it with the necessary voltages:
The huge frequency dial pointer also acts as tuning knob, it does directly operate the main tuning capacitor of the transmitter and receiver sections. Press the two pushbuttons at both sides of the dial pointer to move it, it will lock in 20 kHz steps mechanically. A round thumbwheel lets You detune the set for +/- 50 kHz, to move the dial pointer to another position, set the interpolation tuning knob to zero again. A rotary control „Empfangsnachstellung“ permits to shift the receiver's operation frequency +/- 50 - 100 kHz.
As found in other Zellweger sets, the main switch has it's zero / off position in the middle, turn it to the left for telegraphy mode and to the right for telephony mode, the control also acts as volume control.
Use the antenna tuning control to adjust for a maximum reading on the antenna current instrument when the transmit switch is activated; the meter can be switched to indicate the heaters and anode / B+ voltages, too.
The accessories can be stored in a compartment just below the transceiver chassis: the combined LT / HT battery, the headphones, the hand and the throat microphone and the morse key.
With the switch on the microphone on the „on“ position, the valves of the transmitter stages are heated continuously, in the „off“ position they are switched off and the SE-105 is in „receive“ mode only, when You press the push-to-talk button, You have to wait four seconds until You can start speaking.
The generator is integrated in a case very similar to the transceiver case: a voltmeter indicates, when the necessary voltages for operation are okay or if you have to crank with higher speed to generate the heaters / LT voltage of 5,7 V ond the anode / HT voltage of 120 Volts. A rotary switch allows you to reduce anode / B+ voltage from 180 to 90 Volts, the transmitter output power will be reduced to 1 W and you will find turning the crank of the generator a bit easier.
The set's operation range is 3 km in telephony and 5 km in telegraphy mode in not very suited a housing area and up to 180 or 200 km from a optimum location on top of a hill.
In the transmitter, there is an oscillator (1E7G), a frequency doubler stage (1E7G) and two RF output valves (CB220M). The set has plate modulation, the two modulator valves (CB220M) supply enough output to modulate the plate voltage. Valve V6 (1E7G) acts as microphone amplifier, valve V7 as audio frequency oscillator for the modulation in A2 mode.
The receiver is a single conversion superhet with double use of the three double pentodes V5 - V7.
The signal coming from the antenna is mixed in valve V5 (1E7G) to generate the intermediate frequency of 465 kHz, the second pentode system acts as oscillator. One system of each valve V6 (1E7G) and V7 (1E7G) acts as a double stage AF amplifier. The second system of valve V7 acts as audion (regenerative demodulator), the second system of V6 as AF amplifier, the set only gives headphone output.
In the transceiver, only two kinds of valves are used: The quite „exotic“ double pentodes 1E7G and power pentodes CB220M. These two kinds of valves made by Tungsram in Hungary could be acquired even during war time to produce a sufficient number of sets:
V1 (1E7G, transmitter oscillator); V2 (1E7G, frequency doubler); V3 (CB220M, RF output stage); V4 (CB220M, RF output stage); V5 (1E7G, TX: rectifier for the measurement of plate current; REC: oscillator / mixer); V6 (1E7G, TX: microphone amplifier; REC: 1. IF amplifier, AF amplifier); V7 (1E7G, TX: audio frequency generator for [A2]]; REC: 2. IF stage, audion); V8 (CB220M, modulator); V9 (CB220M, modulator).
Based on their experience with the construction of the K set, the Zellweger company developed the low power patrol radio P-Gerät and the more powerful set P5 with a transmitter output of five Watts in 1942. In 1944, there was also demand from the Air Force and anti aircraft units for a similar set, but valve supplies from Tungsram werde exhausted. So production was changes to different still available valves and 405 units (or according to the documentation „Funkstationen der Armee“ 400 units for a price of 4'900.- Fr. each) could be acquired, the sets were in use from 1945/47 until 1965 and have been liquidated in 1978.
In the forties, the signal squad of an infantry regiment consisted of five signal patrols; two each of these, two P sets and later P5 sets and four bicycles have been assigned.
A typical „Wireless Radio Patrol“ consisted of four men: a corporal (sergeant) acting as group commander, a radio operator, a writer and one person operating the generator. These radio patrols had to march on foot or could ride bicycles.