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====== SE-450 / II (SF station / LF station) ======
**Radio station SE-450 / II** or **High Power radioteletype station** (with 1000 W power amplifier) resp. **Low Power radioteletype station** (with 400 watt power amplifier); manufactured by [[SRT]].

With the introduction of the [[ARQ]] operation, a radioteletype mode with automatic error correction, which is also referred to as SITOR, the [[embassy radio]] stations and the mobile stations for training were equipped with new station material.

Most of the radio station equipment now came from [[SRT]], the [[ARQ]] modem from [[Philips]]. Earlier, a configuration with the modified Siemens 1 kW transmitter as power amplifier stage was used, even longer in some embassies abroad.

The 1000 W solid state power amplifier from [[SRT]] was only used at the Swiss embassy radio communication central, all older morse telegraphy stations still in use were replaced by the variant with the solid state 400 W amplifier.

{{:images:se-450ii-botschaftsfunk.jpg?direct&500|Embassy radio SF station}}
===== Technical data =====
{{ :images:se-450ii-front.jpg?direct&350|SE-450}}
  * [[Principle]]: radio station consisting of separate [[transmitter]] and [[receiver]]
  * [[Receiver]]:
     * [[CR 91]] from [[SRT]]: [[Double conversion]], [[IF]]: 1st IF 125.2 MHz, 2nd IF 200 kHz
  * [[Transmitter]]:
     * Transmitter exciter [[TD 90]] from [[SRT]]
     * Power amplifier 400 W: **SSA 400** from [[SRT]]
     * Power amplifier 1000 W: **SSA 1000** from [[SRT]] (only at the Swiss embassy radio headquarters)
  * [[Modes]]: [[A1]] for emergency communication, [[A3J|SSB (A3J]], ISB, [[F1]] (FSK telegraphy), AFSK / SITOR ([[ARQ]]/FEC)
  * [[Frequency range]]: 1.5 - 30 MHz (reception 10 kHz - 30 MHz)
  * [[Sensitivity]]: according to the data of the receiver in use
  * [[Output power]]: 1000 W eff.

==== Power Supply ====
  * [[Mains]]: three-phase mains 3 x 380/220 V
  * [[Generator]]: ONAN JB 6 kVA, 3 x 380/220 V petrol generator on single axle trailer
The entire power supply of the stations was controlled from a central control panel **ST 84**. With the MAIN Switch, the station can be operated from the local AC network or from a generator in case of an emergency or power failure,  this can be started and stopped by remote control. Timed operation for automated reception and transmission of messages during the night hours with best propagation conditions can also be activated on the ST 84 control panel.\\ 
With the METER SWITCH, the three phases of the mains network or of the generator can be checked. A Schaffner FR 211 line filter is used to filter out interference pulses from poor quality mains network which could impair the functioning of the station.\\ 
Voltage regulators were sometimes used to compensate for unstable mains voltages. In countries with a 60 Hz mains frequency, a 220V voltage with a frequency of 50 Hz must also be prepared for the teletype machine [[PACT-220]].

==== Dimensions ====
The training mobile radio station was installed on a Berna 4x4 truck, the generator in a single-axle trailer.

==== Accessories ====
  * Antennas
     * **AGD antenna**: 2 - 13 MHz, 1 kW max. load; dipole with a distance of 30 m between the masts
     * **AGV antenna**: 9 - 30 MHz, 700 W max. load; four segment mast antenna
     * Roof antenna on the truck; only for training purposes, low transmission power
  * Antenna selector [[ASU 84]]
{{:images:botschaftsfunk-sf-station-relais-new-delhi.jpg?direct&600|SF station New Delhi (relay)}}
===== Station equipment =====
The centerpart of the radio station is the [[TD90]] exciter transmitter driving a solid state **SSA 400** power amplifier or a 1000 W power amplifier **SSA 1000** in the embassy radio central; in the embassies, usually the final stage of the 1 kW Siemens transmitter continuied to be used as power amplifier.

At the control desk, the ARQ modem **[[STB 750]]**, the tranmitter control unit **[[TCU 90]]**, the receiver [[CR 91]] and the transmitter exciter **[[TD 90]]** are located.

The ARQ modem **[[STB 750]]** made by [[Philips]] generates the SITOR signal ([[ARQ]]). The SITOR teletype mode is an FSK radioteletype mode with error correction for omitted characters.\\ 
For "point-to-point" connections between two stations, the radio station works in ARQ mode ("automatic repeat request", SITOR-A). If one character fails, the opposite station requests the transmission of the character again. For broadcast messages, the station is set to FEC mode ("forward error correction", SITOR-B), in which characters are transmitted twice with a time offset.\\ 
Only for emergency situations, F1 (FSK) standard teletype mode 50 Bd without error correction is provided. For service communication, an SSB voice radio channel is programmed; a Mikrotel is connected to the control unit for this purpose. Transmission in Morse telegraphy [[A1]] is only possible in exceptional cases.

All functions of the station can be controlled from the control unit **[[TCU 90]]**. The frequency memory and station identifier are called up in various modules.

{{ :images:se-450ii-srt-cr91-front-b.jpg?direct&400|Receiver CR 91 (SRT)}}

The receiver used is the double conversion **[[CR 91]]** from [[SRT]], which provides sufficient frequency stability for ARQ operation.

The exciter [[TD 90]] provides an RF output power of 100 mW in the complete fequency range 1 - 30 MHz and drives the power output stage in use.

{{ :images:se-450ii-srt-td90-front.jpg?direct&400|Exciter TD 90 (SRT)}}\\ 
The transmitter power amplifier consisting of the final amplifier of the original 1 kW FSK transmitter from Siemens [[S-502]] can be remotely operated. The power apmlifier can be tuned to the 1.5 - 30 MHz range in three ranges: 1.5 - 4/4 - 11/11 - 30 MHz.\\ 
During the eighties, the tube power amplifier was replaced by the solid state power amplifier **SSA 400** with a power of 400 W, only at the Swiss embassy radio headquarters, the 1000 W power amplifier **SSA 1000** was used.

As teleprinter system to print the messages, instead of the noisy rattling teletype machine Siemens [[Stg-100]], an electronic teleprinter [[PACT-220]] from [[Philips]] was used.

From 1995 on, the **MVS** messaging system was introduced, so transferring messages to punched tape was no longer required. A switch automatically selected between the teleprinter or the MVS as the output channel.

The antenna selector **ASU-84** (Antenna Switch Unit) feeds the RF to the antenna system, the station has an automatic antenna tuner **KGA**.

===== Technical principle =====


==== development ====
{{ :images:se-450ii-srt-ssa-400.jpg?direct&400|SE-450: SSA 400}} The original centerpart of the station, the 1 kW F6 transmitter, was developed by Siemens in 1969, as were the teleprinters. Instead of the [[E-629]] (Collins 51J-4) receivers in the original configuration from 1979, the [[CR 91]] was used after changing over to the ARQ error correction mode.

Also in the mid-1980s, the Siemens power amplifier was replaced by a solid state power amplifier from [[SRT]], usually the **SSA 400** and in special cases the more powerful 1000 W unit **SSA 1000** was used.

==== Field use ====
The radio station [[SE-450]] was used for [[embassy radio]] communication, the mobile stations with the same setup were procured for training the staff in Switzerland and foreign embassies; in around 1984/85 the station equipment was modernized and converted to radioteletype with automatic error correction.

In regular operation, the foreign embassy stations operated on timed control. A timer on the main control panel activated the station at a pre-programmed times, the frequencies were selected according to the propagation conditions at the planned transmission time. Only as exceptions, the station could be powered up manually.

For use in crisis regions, there were plans to construct some stations as container stations.

{{gallery>:images?se-450ii*.jpg&0&80x80&lightbox&showtitle&titlesort}}

===== Technische Unterlagen =====

==== Weitere Informationen ====