Jamming Service. (Funk(Mess)-Stördienst).

 

 

       
 

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Jamming of Oboe.

 
         
 

 

 
 

A Mosquito B Mk XVI has just marked a target.

 

The crest of RAF 109 (B) Sqn, the pioneers of Oboe.

 
     
     
    Oboe was the most precise navigation system employed by any air force during WW II.  Operational usage was implemented in late 1942 and the system was used extensively by single Mosquitos attacking pinpoint targets or by Pathfinders marking the target.  For an in depth description please see: Oboe - AMES Type 9000. Briefly told the system worked as follows:  
     Two ground stations were used, which emitted trains of pulses on the same carrier frequency, but with different recurrence frequencies. The aircraft carried a responder, which replied to the interrogations of both ground stations so that each knew the range to the aircraft.

   In the bombing application one of the ground stations was known as the tracking station and the other as the releasing station. The aircraft was caused to fly on a course of constant radius about the tracking station, the radius being such as to bring the aircraft over the target. When the aircraft arrived at the calculated point of bomb release, (that is to say, when it was at a precise range from the releasing station) this station sent a signal, which automatically released the bombs.

   The train of pulses from the tracking station, which commonly had a recurrence frequency of 133 pulses per second was modulated by Morse signals to convey information to the aircraft. Thus if the aircraft was at too short range a series of dots were sent; if at too great a range, a series of dashes were sent when the aircraft was on track, a constant tone like from a oboe was heard - hence the name Oboe. Additionally various letters in Morse code  were sent (A, B, C, D and ST) to denote certain distances from the release point.  See illustration below.

 
     
 

 
 

The principle in Oboe.

 
     
     
 

 
 

The principle in Oboe in the run-up to the target.

 
     
     
  The following description, which to the best of my knowledge is published for the first time in English, is based on the memoirs as published in: "Bumerang.  Ein Beitrag zum Hochfrequenzkrieg", A. Dahl, J.F. Verlag, München, 1973".  
     
     
 

„Man soll diese lächerlichen Holzflugzeuge nicht zu ernst nehmen."

 
 

Order from Lw.Bef.Mitte.

 
     
      The attacks by the single Mosquitos in the Ruhr area, starting in the winter of 1942 - 1943, were a particular problem to the Germans.  In most cases the Flugmelde Dienst did not detect the approaching aircraft either aurally or by radar, so the first indication of an attack, was when a bomb with great precision hit a pin-point target in the Ruhr area.  A very enterprising Hpt. Alexander Dahl with the Flugmelde Dienst of Luftgau VI set about to solve the problem.  After some experiments initially aimed at producing a better sound locator, he was told by his colonel to do: "What ever it takes" to solve the problem.  In his spare time Dahl was an radio amateur, and against all regulations he combined the receiver of a Korfu (Naxos, 3 Ghz) with the reflector of a discarded Würzburg A.  The result was a piece of equipment, which could receive signals from the approaching Mosquitos as soon as line of sight was established.  No doubt due to the very high antenna gain, and an ability of the Naxos also to pick up multiple high and low harmonic frequencies, the system actually covered a wide frequency band.  Dahl used to impress his commander by always having a hot cup of coffee ready, when the commander arrived.  Asked how he did that, he responded that the system picked up the emission from the ignition system in the commanders car minutes before it arrived.  The system was later modified with the Domeyer receiver (200 - 300 Mhz).  This was the Naxburg.  The system was thus able to pick up the signals from Oboe Mk I and II.  It was - wrongly - the belief at that time - and this is repeated in much of the published literature - that the signals picked up emanated from the H2S.  Eventually it was established that the signals did not originate from H2S, but from a different system, by the Luftwaffe called Bumerang (this was Oboe Mk I).  
     
      7 Naxburg Stelle were established in the Ruhr area and a radar was provided to the Stellung KOMET at Huckingen in order to provide for radar tracking, when an aircraft had been detected.  After having observed a number of attacks, Hpt. Dahl and his unit - which incidentally consisted mainly of Ln-Helferein issued with trousers, since they were now field deployed - were able to track attacking aircraft, and intercept the Morse signals exchanged between the aircraft and the ground station.  Based on their understanding of the signals thus exchanged, and the projected flight path, Dahl's unit could forecast the target/target-area 8 - 10 min in advance, and issue an appropriate air raid warning.  All reports were compiled into a consolidated picture at the Funksonderstelle by Lg VI in Münster.  This unit also performed jamming control.  
     
 

 
 

A Ln-Helferein in suitable field uniform.

 
     
     
      A few month later Dahl's unit was provided with 12 Karl jammers, please see below.  These jammers were deployed along the flight path of the attacking aircraft, which was a circular route from the North or South centered roughly on Dover.  Based on the principle of interrogation pulses being responded to by transponder pulses from the aircraft, it was possible - when the right frequency had been found - to transmit false pulses, which were repeated by the aircraft receiver and retransmitted to the ground station.  This completely destroyed the systems ability to do accurate distance measurements.  The first night the Karl was employed, Dahl watched with much satisfaction, how Mosquito after Mosquito had to abandon their bomb run.  The jammer however became ineffective, when Oboe Mk III working on 10 Ghz was introduced and the Anti-Bumerang D jammer was introduced as a countermeasure.  Dahl's makeshift organization eventually became official as Funk.Aufkl.Abt. (Mot) 359 in late 1944.  
     
      The deployment of the Naxburg was not limited to the Ruhr area, at least 3 systems were deployed in Denmark in late 1944.  
     
     
         
 

 
  The Naxburg Stelle.  
         
         
  Map of Anti-Bumerang Stelle.  Some of these are the original Karl Stelle.  They were served by 19 - 22/Funk.Aufkl.Abt (mot.) 359.  
     
 

Example of an Anti-Bumerang Stelle.

 
         
         
 

 

 
 

Dahl's happy band of amateurs who constructed the first Naxburg in the Stellung Efeu in Hochelten near the Dutch boarder.

 

A pair of field deployed Naxburg in the Stellung Maibaum, above the Kettwig Stausee east of Heiligenhaus (Stellung Heidschnucke).

 
     
  Copied and published without permission from the above mentioned source.  Maj A. Dahl would understand and forgive.  
         
 

 
 

Map depicting location, name and function of Luftwaffe Funk(Mess) Stör Stellungen in Denmark.

 
         
 

 
 

The RV-Stellung associated with the Funkstör Stelle in Denmark.

 
 
           

Jamming equipment employed against Oboe.

 

Name

Manufacturer

Frequency

Victim

  Anti-Bumerang A Karl Lorenz 200 - 250 Mhz Oboe I/G-H
Anti-Bumerang B  Feuerzauber * Lorenz 3050 - 3300 Mhz Oboe II
 
     
     
  At the end of the war the Luftwaffe had 70 Karl jammers in operation against Oboe and 54 against G-H.  
     
   
  Karl jammer.  From a German wartime manual, thanks to Jos.  
     
  Victims see: [X.0] Appendix Equipment Quick Reference & Index  
         
         
         
 

 
         
 

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