Jagdschloss Radar - Production Units

Production Units

Although the system demonstrated its utility, further units were not ordered until the fall of 1942, likely due to the increasing tempo of RAF Bomber Command's night offensives at that point in time. Production Jagdschloss units were larger than the original prototype, with an antenna 24 m (79 ft) wide and 3 m (9.8 ft) tall. New electronics were built for the production units, operating on one of two bands; 1.2-1.9 m or 1.9-2.5 m. The first production sets were delivered by Siemens & Halske at the end of 1943, and when production ended in April 1945 a total of 80 units had been delivered.

Jagdschloss units were found to have several "dead spots" due to the antenna being located on an 8 m (26 ft) high tower. For instance, an aircraft flying at 6,000 m (20,000 ft) altitude at any range between 60–80 km (37–50 mi; 32–43 nmi) would be invisible because the direct reflection from the aircraft would interfere with the one reflecting off the ground. This problem was initially solved with the addition of a large wire mesh under the tower, known as Reflektor-Netz.

A more convincing solution to this problem was deployed as Jagdschloss Michael. Michael added a second antenna on the "back" of the original, operating on a 50 cm wavelength system from Telefunken (almost certainly adapted from their Würzburg radar). Range was also increased from the original 150–300 km (93–190 mi; 81–160 nmi), which required an improvement in the angular resolution in order to maintain the ability to resolve aircraft. To achieve this, Michael used a new 50 m (160 ft) wide antenna replacing the older 24 m one. The antenna was so large that the mounting had to be re-designed, with the antenna supported by rollers running in a track as opposed to being mounted off a central shaft.

Another cm-wavelength experiment was built at Werneuchen, east of Berlin, known as Jagdschloss Z. This system operated on a 9 cm wavelength, which was very short for the era. The antenna was built up from the center sections of the Würzburg radar's parabolic dish, stacked vertically to form a single 72-wavelength aperture antenna.

Jagdschloss units of all types were optionally fitted with the Erstling IFF system. Like British IFF units, Erstling fed back its own return upon reception of a Jadgschloss signal. The return signal was slightly delayed, appearing as a second "blip" on the radar screen, allowing the operator to visually identify friendly aircraft. Unlike British systems, Erstling apparently sent back a morse code signal in return.

The FuG25a "Erstling" had two encription keys inside, each of 10 bits. One called "Reichskennung" and the other "Verbandskennung " (squadron key).

A related system, Jagdhütte (German: "hunting lodge"), is also mentioned in reference to Erstling. This was a reduced version of Jagdschloss without radar receiver, operating only with the IFF Signals from Erstling. This was for control of own fighters only. Due to the different transmit and receiving frequency it was resistant against window.

Another optional system for use with Jagdschloss was a remote PPI display known as Landbriefträger (German: country mailman). This allowed the display from a Jadgschloss site to be sent via telephone lines to the flak defenses so they could arrange their attacks locally. Signals from the original Tremmen and the later Werneuchen radars were forwarded to the flak tower at the Berlin Zoo.