VHF radio station SE-411; manufactured by Autophon AG, Solothurn.
In addition to the SCR-608 radio sets acquired from U.S. Army surplus, there was an additional need for vehicle stations. After they had developed a prototype set in 1953, Autophon got the order to develop a powerful VHF radio station. In 1957, their new sets SE-407 und SE-411 were introduced, 262 sets of the shortwave station were produced. Only in the seventies, this powerful but heavy and large set was replaced by the American AN/VRC12, in Switzerland called the SE-412 .
The station has twelve mechanical preset frequencies in its frequency range 24.1 - 35 MHz and has a modular design. The system consists of a transceiver, the power supply and an auxiliary receiver, which is used for example to receive the messages of the superior commander. An AF amplifier and an amplifier for the on-board intercom for use onboard a tank are integrated in the mounting frame.
The SE-407, developed for for the needs of the artillery and the airforce / anti-aircraft units, covers the frequency range from 24.1 - 35 MHz with 110 channels, it consists of the transceiver TR 96, auxiliary receiver ZE 96 and the Power Supply SG 83.
The variant SE-407 with the frequency range of 34 - 50 MHz in 161 channels was designed for use in infantry and the armoured corps. Its components are transceiver TR 83, auxiliary receiver ZE 83 and the same power supply unit SG 83.
The NF amplifier NV 83 and the amplifier BV 83 for the on-board intercom are integrated in the mounting frame MR 83.
The actual transceiver TR 96 is installed on the left side of the mounting frame, it has a modular design ans it's dimensions are 302 x 260 x 340 mm and 23,2 kg. In the transmitter part, the signal of the oscillator common to transmitter and receiver circuit (range 24.1 - 35 MHz) is fed via an amplifier and driver stage to the two output valves in a push-pull arrangement, the RF is fed via an antenna coupling tuning unit to the antenna.
The incoming signal amplified in the input stage of the receiver and mixed with the local oscillator signal 8 MHz above the operation frequency. The resulting first intermediate frequency of 8 MHz is converted to a second IF of 1.6 MHz and the signal has to pass a limiter and is demodulated.
The power supply provides the necessary voltages for the transceiver, the auxiliary receiver and other modules. It is powered from the vehicle operating voltage of 12 or 24V, the correct voltage must be set on both the power supply and auxiliary receiver and also with two toggle switches on the mounting frame.
The auxiliary receiver ZE 96 is almost identical to the receiver part of the TR 96; with its dimensions of 212 x 260 x 340 mm and „only“ 21.1 kg, it is slightly smaller. It is to monitor traffic from a superior command while messages are exchanged with another station on a different frequency with the main transceiver. Stand-alone operation of the auxiliary receiver is only possible with an auxiliary receiver control unit, which will significantly reduce the value of a ZE 96, which was partly sold on it's own as military surplus.
A core component of the radio system is the „instantuner“ used in the transceiver as well as in the auxiliary receiver. In the „instantuner“, the oscillator signals for the channels in 100 kHz steps are generated and the mechanical presets for twelve frequencies are contained.
Different control units are used to recall the preprogrammed channels, the audio signal of the main transceiver, the auxiliary receiver or messages from the on-board intercom (in an armored vehicle) can be selected. There is also provision of a remote control unit operated over field telephone lines. The auxiliary receiver control unit ZBG 83 is necessary to control the auxiliary receiver.
There is a large number of other accessories like an external loudspeaker LS 83, the microtel (a telephone handset with a push-to-talk button typically used by Swiss armed forces) and a noise set with headphones and lip microphone; there are different antenna sets to fit the SE-411.
In the transmitting section, the signal of the common oscillator O1 (range 24.1 - 35 MHz) is fed via an amplifier and driver stage to the two push-pull RF output tubes and via an antenna coupling and tuning unit to the transmitter antenna. A small inductance at the oscillator circuit, which is connected to the modulation diode via the microphone slightly affects the oscillator frequency, so frequency modulationis generated.
The frequency is processed in the AFK section („automatic frequency correction“): The spectrum of a basic oscillator O2 (up to 27 MHz) is superimposed to the signal of the oscillator O1 in the mixer M2. The resulting intermediate frequency is filtered out in a 22.1 - 23 MHz bandpass and fed to the mixer M3.
In the „instantuner“, the motor tuning unit, the crystals of the shift oscillator O3 are located; the output frequency can be set in 100 kHz steps and is fed to mixer M3, where an IF of 3.5 MHz is generated. This signal is fed to the quartz discriminator, which converts the deviation from the nominal frequency to a DC voltage, which corrects the frequency of the oscillator O1 to the desired operating frequency via the reactance tube.
In the receiver, the incoming signal is amplifiied and mixed with the local oscillator signal O1 (range 32.1 - 43 MHz) (M1) oscillating 8 MHz above. The frequency is stabilised the same way by use of the reactance tube as the transmitter frequency. The resulting first intermediate frequency of 8 MHz is mixed and converted to a second IF of 1.65 MHz. After three IF amplifier stages, the signal has to pass through the limiter stage and is demodulated in the discriminator.
As one of the first Swiss Army radio stations, the SE-411 instructions no longer contain any information about replacement of tubes, these duties are entirely left to the signal mechanic, so the signalmen operating the set do not have to take care of this.
Beginning in 1953, Autophon developed the unit as a Swiss alternative to the American surplus SCR-608, which is also a frequency-modulated VHF radio; the new station should use fewer of the expensive quartz crystals.
In 1957/60, a number of 262 units of the the Autophon SE-96 were acquired and introduced as SE-411 in the infantry and the mechanized troops.
The standard operation distance was 15 km in hilly terrain, 30 km in open terrain and in case of direct line of sight (on VHF frequencies, propagation is similar to optical light) up to 200 km.
In addition to the use in armored vehicles, the station was also used in signal trucks (VW bus or Mowag). In order to be used as a relay staion, these vehicles were also equipped with a radio from the SE-206/09 family, depending on the intended type of service.