In 1938, the Swiss Army called for offers for a mobile wireless station, as the early Swiss military wireless stations came on a limber, this was in the specifications for this new station, too. Offers came from C. Lorenz AG, from Telefunken Zurich and also from the small Swiss company Zellweger, Uster. The later proved very good results in trials, so after a very hard effort, the first production run of stations could be put in service in 1940/1.

The newly developed transmitter was not only installed on a trailer - this arrangement got the designation "Fahrbar Leicht 40 / FL 40" - but also as "Tragbar Schwer / TS 40" (portable heavy wireless station), on a truck as replacement of the longwave / shortwave station Telefunken ("Kurz - Lang 43 / KL43") and as motorized wireless station 44 ("M44").
The famous all wave receiver "Uster" / E41 was used as standard receiver to replace older equipment on several high power stations, until it was later replaced by the Autophon E-627.

The complete wireless station came installed on two one axis carts, one of them called "apparatus trailer" with all electronic equipment and an attached telescopic antenna and the other one "machine trailer" with a fuel or electric driven generator providing all necessary voltages and space for all necessary accessories and antenna components.

The receiver of the wireless station FL40 was the Receiver Uster E41, a single / partly double conversion receiver with battery valves and coil sets for the different wavebands as found in the National HRO.

The FL40 transmitter comes in a huge case with carrying handles and ventilation holes at it's sides - it is portable, in the strict meaning of the word: You can carry it...
The transmitter covers the longwave ranges 190-242 / 242-400 / 400-715 kHz and the shortwave ranges 1500-2300 / 2300-3300 / 3300-4500 kHz, a crystal permits to calibrate the set for 4000 kHz.

For shortwaves, the FL40 uses a telescopic mast attached to the "apparatus trailer", a seven parts mast made from plugged elements or a L antenna erected between two 10 m poles, for longwaves, the latter antenna arrangement is used, too.

The station is powered from a petrol operated or electric motor that can be coupled to a special generator, the three phase electric power (50V / 150 Hz) is fed to a rectifier to generate the necessary plate / anode voltages of 300 and 1250 Volts for the transmitter and the anode / HT voltage of 120 V for the receiver as well as 6 V for the heaters and accumulator charger.
A inverter generates the necessary 120 V anode / HT voltage for the receiver E41 in case the generator is switched off or for remote operation of the station, a 6 V accumulator will also be used for heaters operation directly.

The FL 40 has been faded out in 1961 and has been replaced by the famed Zellweger SE-222 set.