This receiver was a part of the Fu 18 configuration, used for acoustic artillery fire detection. Four or five (depending on configuration) microphones were buried in the ground. When an enemy howitzer fired a shell, the microphones registered the sound, and the four (or five) connected transmitters would send the sound to four (or five) receivers in another vehicle (Sd.Kfz. 251/14). The receivers were connected to a machine that would graph the impulses on paper or wax tape, which would in theory determine the location of the enemy artillery. This technology was used first in WWI with limited success. The problem was with a) proper placement of the microphones, and b) with uneven terrain. Sound would bounce off of hills creating distortion to the impulses, or if the microphones were buried too far away, the artillery fire would sound more like a rumble - not really a good signal for the system. Since this method was not very successful in the WWI, there probably were not too many of these configuration deployed, hence the low serial number of this receiver.

Translated from "Die deutschen Funknachrichtenanlagen bis 1945 - Band 3 "Funk- und Bordsprechanlagen in Panzerfahrzeugen " by Hans-Joachim Ellissen

Two variations of these devices were introduced for sound-measuring purposes. They differed based on the number of sound measuring points utilized (20W.S.b respectively and after 1943 20.W.S.b1) and sound recording (listening) configurations (Ukw.E.b1). In the documentation D976/3 from 03/01/1940 three variations were described in the pages of the War Equipment Report (K.A.N.(H) from 07/01/1942 the variations were for either 4 or 5 listening points existed specified as Fu 18 by evaluation task force.

Below is the inventory of the listening vehicle

4(5) Ukw.E.b1 receivers
1 Loud-speaker "L.S. (Fu) 1"
1 Umformer EUaS at 4, EUaS1 at 5 Ukw.E.b1
1 Frame FuS (4E), FuS1 (5E) for the above devices
1 Frequency tester "b"
1 Rod antenna "b" (5/2.5) (5 meter mast, 2.5 meter antenna)
2 Batteries "12 B 105"
(1 Generator GG 400 z. to charge the batteries)
1 Vacuum tube tester "a"

The sound recording / transmitting vehicle was an Sd.Kfz. 251/14. The inventory of the sound recording and transmitting vehicle was:

4(5) 20 W.S.b or b1 transmitters
4(5) rod antennas "b" (5/2.5) (5 meter mast, 2.5 meter antenna)
4(5) Umformers "U 20 aS" or a1S
4(5) Generators GG 400
12(15) Batteries "12 B 105"

To record the sound pulses in the listening vehicle there was a "light pen" or a wax/smoke writer (a choice of smoked paper or wax paper tape 65 mm wide) with four amplifiers for the four sensing loops (one more if there were five Ukw.E.b1 receivers). The amplifier was designed with two RV2,4P700 and one RL2,4P3 vacuum tubes (1943), and in older designs with the RL2P3 tube. The power source was from a 2,4NC28 battery and two anode batteries connected in series (90 V and 30 V).

In the host-SPW, in addition to the optical data measurement microphones, prisms, and including artificial antennas 20a carried for the radiation-free tuning of 20W.Sb (1).