FuG 25a Erstling

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FuG 25a Erstling
An Erstling coding unit
Country of origin Germany
Introduced 1941
Type Identification Friend or Foe (IFF)

The on-board radio set FuG 25a Erstling (German: "Firstborn", "Debut") was a dual-band (mid-VHF and low UHF) identification friend or foe (IFF) system installed into Luftwaffe aircraft of World War II starting in 1941 in order to allow German radar stations to identify them as friendly. Developed by the GEMA company, it received impulses from German Freya or Würzburg radar stations and replied with a pre-defined signal. Later, the FuG 25a became a key component of the EGON night fighter guidance procedure.

Although ground receivers could use the encoded signal to determine whether the return signal was properly encoded, the system did not have any system allowing the transponder in the aircraft to reject signals, and would reply to anything displaying the proper frequency. The British used this in their "Perfectos" detectors, which were able to home in on the Erstling signals without their knowledge.


The "Erstling" IFF transceiver was activated from ground stations by switching the pulse repetition frequency from 3,750 Hz to 5,000 Hz. The on-board device replied by sending a pre-programmed morse code signal on 156 MHz. The coding unit was a motor-driven Cam Switch encrypted with two ten-bit code keys.

Würzburg stations needed to be equipped with accessory units, namely a query transmitter code-named Q-Gerät ("Kuh", German "cow") and the identification receiver "Gemse" (German for "chamois").


In the summer of 1944 the first British Mosquito aircraft were equipped with the "Perfectos", a device that activated the FuG 25a and triggered the response, which was detected to reveal the presence of the enemy aircraft. This severely curtailed the use of "Erstling", as German night fighter crews had to switch it off to avoid detection.[1] A number of German night fighters were shot down by German flak forces when they switched off their units.[2]

Technical specifications[edit]

  • Receiver: 125 MHz (Freya) and 550-580 MHz (Würzburg)
  • Sensitivity: 2 mV
  • Transmitter: 156 MHz
  • Power: 0.2 Watt
  • Activation: Radar pulses at 5000 Hz
  • Encryption: 2x10 bit
  • Range: 40 km (FuG 25z) and 270 km (FuG 25a)
  FuG 25z FuG 25a
Reception frequencies 560 MHz 125 ±8 MHz
Transmission frequencies 560 MHz 156 MHz
Transmission power unknown 400 W (PEP)
Current 4 A DC 4 A DC
Power supply 24 V DC 24 V DC
Weight 11 kg 17 kg
Tubes 6xRV12P2000, 1xLD1 7xRV12P2000, 1xRG12D60, 2xLD1, 1xLS50.
Range 72 km (40 miles roughly 80% of visual range, max. 270 km (150 miles)


The Luftwaffe was known for fitting sensitive devices like "Erstling" with small explosive charges to allow their destruction in order to avoid capture. A short fuse allowed the crew to reach a minimum safe distance.

See also[edit]


External links[edit]


  1. ^ Gebhard Aders, Geschichte der deutschen Nachtjagd, Motorbuch publishing company 1977, p. 303
  2. ^ Price, Alfred (2015). The Last Year of the Luftwaffe: May 1944 to May 1945. Frontline Books. p. 94.