In 1919, six stations "Funken - Kleinstation GFuk18" (Spark small station GFuk18) have been orderen from the German "Deutsche Gesellschaft für drahtlose Telegraphie, Berlin" (German society for wireless telegraphy), the later "Telefunken" company.
The station, intended for mobile use, was constructed on two limbers pulled by a horse or an open truck: The "apparatus trailer" and the "mast trailer" with a telescopic antenna mast.

In the first years, the transmitter used was a Telefunken Löschfunkensender 0,4 TV (Telefunken Sparc Gap transmitter 0,4 TV) for telegraphy B2. This could be tuned in the 187,5 - 2000 kHz range, the nominal output power was 400 W, primary power 1000 W.

(F.L. 19, early setup: Receiver E213a (right lower corner), AF amplifier Spez 60 Bs (two valves, left upper corner), Wavemeter (left lower corner), Transmitter 0,4 TV (right cabinet); image from a publication from R. Ritter)

When the signal troops equipment was renewed in the year 1925, the existing F.L.19 stations were improved and ten new stations were ordered: The transmitter with the new arrangement was a Telefunken valve transmitter Zwischenkreissender ARS 87 for telegraphy A1 (CW), A2 and makeshift telephony A3. The transmitter covers the 187,5 - 790 kHz frequency range and has an output power 75 W.
The valves used are a triode RS 19 and a triode RS 55.

Receiver Tfk Spez 7 Bs	Transmitter Tfk ARS 87 (Both images from a Swiss private collection)

In the early setup, the receiver used was a Audionempfänger E213a (Tuned radio frequency with regeneration) covering the 86 kHz - 2000 kHz frequency range, in this receiver, two triode valves RE 11 are used.
In 1925/6 this receiver has been replaced by the Zweikreis - Reflexempfänger Spez 7 Bs (E25) (two tuned circuits) covering the 125 kHz - 2000 kHz frequency range. In this receiver and the audio amplifier (in a separate wooden cabinet), four triode valves RE 062t are used.
In 1931/2, the receiving equipment was replaced by the Telefunken 470 Bs (E31), a very modern and sensitive set in it's years. It came with six triode valves RE 074n and has a frequency coverage of 100 - 1090 kHz.

(F.L. 25, late setup: Receiver E31 / Spez 470Bs (left lower corner), a Wavemeter Spez 125Bs (left, on top of it), Transmitter 0ARS 87 (right cabinet); image from a publication from R. Ritter)

The aerial used was a umbrella antenna on a15 m telescopic mast mounted on the back trailer or a 60 m T or L shaped double wire antenna erected between two 12 m masts.

(K+W official image reprinted in a publication from R. Ritter)

The station was powered from a fuel operated generator.

The "Fahrbar Leichte Funkstation 25" has been finally replaced by the FL 40, constructed by Zellweger, Uster in the year 1941 and want completely out of service after the end of World War II general mobilisation.

(image reprinted in a publication from R. Ritter)