Wireless station SE-222; developed and produced by Zellweger, Uster.

The Swiss Kriegstechnische Abteilung (Departement of Defense Technology) announced a project to replace the pre war shortwave station "TL" in 1950 and made a call for development. After they had already started development work, the Zellweger company could present four prototype stations capable of transmitting single sideband and FSK radioteletype signals. After it showed so reliable after the first troop evaluation, a first batch of 25 stations was ordered in 1956 and larger numbers of the SE-222 as standard shortwave station have been ordered until 1963.

After the use of morse code transmission in the early years, telephony and radioteletype transmission got growing significance. Because of radioteletype transmissions using Baudot code were sensitive to propagation disturbance, the KTA decided in favour of using a unique radioteletype technology developed by Gretag, all letters and numbers could be composed from 14 standard elements (similar to the contemporare 7 element displays for numbers). If one of the bits was missing, the letter remained legible in most of the cases. When the combination of 14 segment ETK code and encryption (KFF 58) was used, even enrypted radioteletype transmission was possible.


Technical Data

Power Supply

  • Mains: 90 - 290 V (nominal 220 V)
  • Generator: 220 V, 800 W (MAG) or 1000 W (Homelite)


  • Transceiver 380 x 420 x 310 mm, 26 kg
  • Power Supply 380 x 420 x 310 mm, 26 kg
  • Accessories case: 380 x 420 x 310 mm, 18 kg
  • Antenna material case: 380 x 420 x 310 mm, 20 kg
  • Bag with mast elements for 13 m mast, 1130 x 150 x 80 mm, 6 kg


  • for mobile use, a 5m whip antenna was used, for fixed operation, a 13 m mast antenna or a 2 x 37 m dipole was used


SE-222 TransceiverSE-222 Power Supply
The wireless station SE-222 consists of two metal chests containing the transciver and the mains power supply / speaker unit; this combination is quite typical for Swiss Army equipment starting with the E39 receiver.

The wireless station could be used for mobile operation mounted on a Volkswagen Bus; a second Volkswagen Bus was used to transport the signalmen operating the station. There was also the possibility to operate the station from a fixed position on a building or shelter; remote control over field telephone lines is possible over a maximum distance of 1.8 km.

When using ground wave propagation, the operating distance in mobile operation was at least 10 - 15 km; during the night hours with a suited antenna and using ionospheric propagation, it could be used for much larger distances.

The stations is powered from the mains, on the power supply, there is a selector for voltages between 92 and 292 Volts. With the usual mains voltage of 220 V, the set will need 140 W in reception mode and 455W when transmitting. The station can also be set up for operation on a petrol generator. The transceiver and the power supply have a weight of 26 kg each, the chests with spares and antenna material another 50 kg.

SE-222 Sendeempfänger On the transceiver front, you find the two large instruments to display signal strength and antenna current; the Revue mechanical clock is usually missing.
In the middle row of controls, from the left, the RF-Gain, just below the AF-Gain / volume control are located. In the middle the dial with a mechanical digital frequency readout; the outer ring of the tuning knob acts on the 100 kHz steps, the inner selects the 0 - 99 kHz digits, frequency accuracy is better then 500 Hz. At the right, next tot the handle, the antenna tuning controls are located.
In the bottom row, you find the connectors for the microtel (microphone / earphone combination with a push-to-talk button), the headphones, the modes selector and the switches for the internal speaker and FSK control. Next are the witchs for tuning and antenna coupling. The remote control switch must be set to LOCAL, in FSW mode, the F+ switch ist used to switch from transmitting to reception (not everybody owns a cryto teletype machine KFF-58 to try encrypted radio teletype mode.

AnschlüsseOn the right side of the transceiver, the connectors for remote operation (using a field telephone F.Tf.50), the morse key, teletypewriter ETK and the cable fro mthe power supply are located, next to it the antenna socket, the earth connectors an the fan.
On the lid, you find a printed table with the standard settings of the antenna tuning controls for some standard frequencies.
At the bottom, you find two small rotary switches and a window, the right instrument can be set to display different voltages and currents of the valves to be used for fault location.

SE-222 Speisegerät On the Mains power supply you pull out the voltage selector switch to set the unit to different mains voltages; with the correct setting, the indicator of the voltage instrument should be in the red coloured segment. If the switch ist set to reception mode, the green lamp EMPFÄNGER should be lit, with operation switch in transmit - receive position, also the red SENDER lamp.
On the left side of the mains power supply, you find the mains fuses, a 12 V connector for a lamp and a 220 V socket (for the teletypewriter), on the right side next to the speaker the fuses for the plate and heater voltages and the multi pole connector for the power supply cable to feed the transceiver.

In a complete SE-222 station, you find several accessories chests with all necessary cables, the morse key, the microtel with the „push to talk“ button, the lamp, replacement valves, cables for measurements for fault detection and a chest with antenna material as well as reels of cables for remote operation.

Technical Principle

In the transmitter the audio signal is fed to a push-pull modulator and mixed with the signal of a 250 kHz oscillator (Osz.13, V202, one system of 12AU7), after a carrier suppressor, the signal has to pass an upper sideband mechanical filter. The valves V304 and V305 are used to switch the mechanical 250 kHz filter from reception to transmission mode and the V306 (5654) divides the signal feed to receiver and transmitter after the mechanical filter. In the second modulator stage, the signal of 251 kHz is mixed with the signal of the variable oscillator (Osz.14, V301, V302, two 5654, 548,5 - 648,5 KHz, used to tune within the 100 kHz range) generate the second transmitter IF, which is variable in the 800 - 900 kHz range. This IF is fed to an amplifier (V303, 5654) and in the thirdmodulator stage, the signal crystal oscillator (Osz. 15, V601, 5654) which can be tuned from 2,6 - 4,3 MHz in 100 kHz steps, to generate the transmitter operation frequency. After two RF preamplifier stages (V101 and V401, two 5654) the signal is feed to the transmitter driver (V402, V403, two 12AU7 in push-pull arrangement) and the the final RF amplifier. It consists of two sets of two final amplifier push-pull valves in parallel (V404, V405, V406, V407, four 6146). An automatic gain control protects the output stage if the antenna coupling is poor by feeding a negative grid voltage to the preamplifier V303 / V305.
V203 is used to monitor the AF from the first transmitter modulator stage.

Modulation is different according to the operation mode: in A1 mode, the signal of the morse key acts on the keying valve (V205, 5654) and a 1,5 kHz oscillator (V206) to be fed to the first transmitter modulator. In A3J telephony, the microphone signal directly and for remote operation over an additional amplifier stage (V108) to the modulator. In FSK mode, the impulses of the ETK(Eintonkombinations) teletypewriter is amplified (V108) and fed to the keying valve V205. Two AF oscillators of 1,5 / 1,8 kHz (V206, V207, two5654) generate the audio signal of 1,8 kHz for space and 1,5 kHz as mark during the impuls of the ETK, even these signals are fed to the first transmitter modulator in a similar manner.

In the Receiver, the signals of the same oscillators (Osz.15, 100 KHz ranges and Osz.14, tuning within a 100 kHz range) are used to generate an oscillator frequency from 1,9515 up to 3,7515 MHz: The signal coming from the antenna hass to pass a band filter and an attenuator and is fed to the first RF amplifier (V105, 5654) and a second RF amplifier stage (V106, 5654).

The signal from the crystal oscillator Osz.15 with its 100 kHz steps is mixed with the signal of the VFO oscillating between 548,5 - 648,5 kHz (Osz.14). So the oscillator frequency variable between 1,9515 and 3,7515 is amplified (5654) and in th first mixer stage (1. Empf.-Modulator) the first intermediate frequency of 251,5 kHz is generated.

In reception mode, valve V304 (5654) is feeding the signal to the mechanical 250 kHz filter and this will come back to the reception path. In an amplifier stage (V209, 5654), the AGC (automat. gain control) voltage is generated. The signal is mixed with the 250 kHz oscillator signal (2. Empfangsmodulator, V210, second system 12AU7) to generate the audio signal.

The audio signal is amplified in the AF preamplifier (V203, 5654), the AF ecxiter stage (V202, one system of the 12AU7) and the AF final amplifier (V204, 12AU7, two triodes in push-pull arrangement), AGC acts on all three AF stages. For F1 reception, the signal is amplified in three limiter stages (V102, V103, V104, three 5654)and fed to the discriminator (made from four semiconductor diodes), after a 80 Hz filter the signal can drive the ETK teletypewriter.

The remote control amplifier (V108, 5654) is used for remote operation.

Valve layout

V101 (5654, 1. transmitter RF amplifier); V102, V103, V104 (three 5654, F1 limiter); V105 (5654, 1. RF receiver amplifier); V106 (5654, 2nd receiver amplifier); V108 (remote operation amplifier) V202 (12AU7, one system Osc.13 - 250 kHz; one system AF driver); V203 5654, AF preamplifier); V204 (12AU7, AF output valve, zwei triode systems in push-pull operation); V205 (5654, keying valve); V206, V207 (two5654, AF oscillator 1,5 / 1,8 kHz); V209 (5654, AGC amplifier); V210 (2nd system 12AU7, 2. receiver mixer stage)

V301, V302 (two 5654, Osz. 14 - 548,5 - 648,5 KHz); V303 (5654, transmitter IF amplifier 800-900 kHz); V304, V305 (two 5654, transmit receive switch of the 250 kHz filter); V306 (5654, transmit receive switching after mechanical filter) V401 (5654, 2. transmitter RF amplifier); V402, V403 (two 12AU7, transmitter driver, push-pull arrangement); V404, V405, V406, V407 (four 6146, two parallel sets of two RF output valves in push-pull arrangement) V601 (5654, oscillator 15, 2,6-4,3 MHz)


In the early fifties, Telefunken was working on a successor for the TL-station, the SE-220, only a small series of this type has been produced for troop trials. At the same time, Zellweger presented a singe sideband station which turned out to be much more powerful and even cheaper then the Telefunken set, is was introduced as SE-222.

The set is of modular construction, some subgroups are mounted in metal cans which look like shielding cans, and they can be plugged in on valve like sockets to make repair works easier.

Even the prototypes of the new station capable of CW, single sideband and FSK operation were welcomed with much enthousiasm when they were introduced in 1954. In contrast to the expectations, single sideband telephony was used rarely, because Gretag had finished development of their ETK, TC53 and KFF machines which gave the possibility of automatic encrypted radioteletype operation.

A totl of 526 units has been produced from 1955/64 and were delivered to the troops after 1958. Over a long period from 1958 - 1987, the major part of military radioteletype communication was sent over one of these very reliable machines.

After 1995, the SE-222 werde liquidated and many of them got in the hands of radio amateurs, because they could be used for standalone operation in the 160 m ham band.

Field use

Technical Manuals

Further Information

en/se-222.txt · Zuletzt geändert: 2019/11/02 20:16 von