This radio direction finder was first built in 1932 by Telefunken. It's total frequency range is 3-20 MHz. This range is divided into three sub-sections of 3 to 6 MHz, 6 to 12 MHz, and 12 to 20 MHz. This is accomplished with three frequency modules that are inserted into the top of the P57N. These modules look like clothes irons. The P57N comes with a set of head phones, a tripod in a canvas-leather carrying case, and a direction locating compass which allows for quick direction determination.

Translation from Die deutschen Funkpeil- und -Horch-Verfahren bis 1945 - by Fritz Trenkle

Based on official request, the Telefunken company introdced the near-field direction finder P 57 N, which was a 6-tube heterodyne receiver with three exchangeable spool modules that spanned 3-20 MHz. The set featured a 50 cm diameter loop antenna, a "help" antenna, and the whole set was rotatable on a direction degree scale that sat on top of a tripod. Camouflage was the most important requirement of personnel who searched for secret agent transmitters, and the P57N could easily be installed inside the wood cabin of a truck such as the Kfz. 17, which also allowed direction finding on the move. This set was manufactured until around 1942 and was issued to the direction finding units.

From the www.hamfu.ch site:

This direction finding set was called the P-701 by the Swiss Army. Between the years of 1935 and 1937, a total of 26 of these sets were ordered by and delivered to the Swiss Army, at a unit cost of 9000 FR (about $150,000 or 110,000 Euro today).