P - Gerät or Patrol Set SE-104; manufactured by Zellweger AG, Uster.
The commonly used set of the infantry radio patrols in the forties was the „Patrol Set P“ or SE-104. It was developed by Zellweger, Uster, as a low power station. The more powerful variant P5 found a much wider use because of it's improved communication range; the signal patrols were equipped with bicycles.
The complete set consists of an apparatus case with the actual transmitter and a battery compartment, which has a weight of 12 kg included the batteries, and a generator case with spares and accessories which makes another 12 kg, the long distance antenna material comes in a canves bag (5.7 kg).
The receiver can be operated either from a combined plate (126V) and heaters battery (6V) or from a hand cranked generator, this generator needs always to be used during transmission, a relay prevents that energy is drawn from the battery during transmission.
The receive - transceive switching is done with the receive - transmit switch in telephony mode and automatically in telegraphy mode, one second after the last character has been keyed, the set automatically goes back to reception mode.
The operation is less complicated than to supply it with the necessary voltages:
The frequency is tuned with the large frequency switch - which also serves as a dial pointer - it drives directly the double variable capacitor of the transmitter and receiver. By squeezing the two buttons at the top of the frequency switch together, it is unlocked to be moved to set the frequency and snaps into 20 kHz stops when released. A knurled wheel at the top of the frequency switch is used for fine tuning of the frequency by +/- 50 kHz, the detent of the frequency switch is only released when the frequency correction is set to 0 kHz to prevent misadjustment of the transmission frequency. A „Reception adjustment“ fine tuning control allows you to shift the reception frequency by +/- 50-100 kHz depending on the setting of the frequency selector.
Like in other Zellweger sets, the modes switch has the 0 position (for OFF) in the middle, for telegraphy mode it is turned to the left, for telephony mode to the right, and volume increases if the control is rotated clockwise for telephony.
When the transmitter is keyed, the antenna tuning must be set to maximum deflection of the antenna current instrument. The instrument can also be used to display the heaters and plate voltages.
The accessories compartment underneath the transceiver accommodates the combined heaters and plate battery, the headphones, the handheld and throat microphone. The transmit - receive switch is integrated into the frontplate as does the Morse key, the latter is folded in when not in use.
Two headsets can be connected to the P set via a double plug. The switch on the microphone allows switching off of one of the two microphones.
The hand cranked generator is built into a case of similar size as the transceiver, a voltmeter indicates whether the required power is sufficient or faster cranking is needed to reach the 120 V plate voltage and 5.7 V heaters voltage. When the generator cable is plugged into the transmitter, the internal battery is automatically inactivated.
The same hand cranked generator can also be used to supply the station K1A. On the rear of the case, there is a compartment with some spare parts for the P station, a valve KF4M, a valve [de:4692]] and the necessary iron-hydrogen resistors.
Communication range is around 0.5 km in telephony and 2 km in telegraphy in unfavorable hilly terrain, under optimal (line of sight) conditions from an elevated position up to 12 resp. 15 km can be reached.
In the transceiver module, the transmitter section is located largely on the right and the receiver section on the left.
The transmitter works with an oscillator stage with frequency doubler (KF4M) and a power amp tube KF4M). The modulation is done as combined plate & screen grid modulation, the tube V5 (KF4M) works as microphone preamplifier, the two IF amplifiers V3 / V4 work as modulator tubes (KF4M) when transmitting. The tube V5 is also used as audio frequency generator for the telegraphy tone in A2 mode.
The receiver works as double conversion: The received signal is mixed in valve V1 (KF4M) to genrate the first intermediate frequency of 1650 kHz, the valve V5 (KF4M) is used in transmission mode as oscillator tube. With the signal of the auxiliary oscillator valve V6 (Philips 4692), it is converted to the second IF of 465 kHz (V3: KF4M), the IF is amplified in two stages (V3 / V4, each KF4M) and fed to the regenerative stage (V2, also a KF4M) for demodulation. Two systems of the tubes V3 / V4 (both KF4M) act as AF amplifiers in push-pull arrangement and provide the AF signal for the headphones.
V1 (KF4M, transmit: oscillator; reception: 1st mixer); V2 (KF4M, transmit: RF amplifier; reception: regenerative stage); V3 (KF4M, transmit: modulator (push-pull circuit); reception: 1st IF amplifier / AF pre-amplifier (reflex circuit)); V4 (KF4M, transmit: modulator (push-pull circuit), reception: 2nd IF amplifier / AF output stage (reflex circuit)); V5 (KF4M, transmit: microphone preamp resp. audio generator for A2; reception: oscillator); V6 (4692, reception: 2nd oscillator).
Based on the experience with the development of the station K1, the Zellweger company developed the „lightweight“ patrol radio P set in the years 1937/38. It was produced in 1939 and introduced with the troop in 1940, where it remained in use until 1952; In 1963, all 334 devices were liquidated.
The station crew of a P station, the so-called radio patrol, consisted of 4 persons: a corporal as station leader, a radio operator, a clerk and a „Kurbler“ („cranker“, to operate the hand generator). Depending on the mission, the patrols were on foot or by bike. As standard, telegraphy was used; the Morse key was integrated on the front panel of the set and could be folded out.