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Luftboden-Empfanger-Programm
On 1939 was specified by the German Air force “Reichsluftfahrtministerium” (RLM) five types of similar receivers, covering the entire frequency spectrum from Long-waves (40 KHz) to VHF II (150 MHz), intended for use in the Luftwaffe ground stations, but also for other military services and authorities. A request for quotation went out to a few German electronics manufacturers.
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Telefunken was finally chosen to develop and manufacture the series of receivers according to their specification ”Luftboden-Empfanger-Programm”
On 5 May 1941 Telefunken presented to the military authorities the early receiver prototypes and details of project in the document called: "Luftboden- Empfänger-Programm" 2 – 7500 m für die Bodenausrüstung der deutschen Luftwaffe”:

E51 "Leipzig" 40-1600kHz (long wave) early prototypes
E52 "Köln" 1,5-25MHz (short wave) early prototypes
E53 "Ulm" 24-65MHz (VHF I) in development
E54 "Kulm" 60-150MHz" (VHF II) projected

The originally planned E54 "Kulm" was changed to E54 "Ulm B" with the new range 21,5-120MHz.

Only one original copy of this document still survives at the Arthur O. Bauer collection.

Only the models E52 Koln and E53 Ulm was really produced but only E52 Koln was finally produced in large scale: about 2400 to 2600 units, until the end of the war.
The receivers are modularized, the modules are mounted in a very advanced modular aluminum chassis and all connections between the modules are through connectors in a motherboard on backplane. Both the construction and the performance were far ahead of its time. Only one type of valve, the RV12P2000, was used in the receiver: 10 for E52 Koln and 12 for E53 Ulm, except for two power rectifiers tubes RG12D60.
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RV12P2000 Tube

The intention was that all modules and valves should be interchangeable in the field without the need of realignment.
E52 Koln
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Telefunken E52a Koln

History
The development of the receiver E52 Koln can be considered the evolution of Telefunken T9K39 Main project with improvements and simplifications.
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T9K39 Main

Early prototypes had maintained different elements of T9K39 Main like the band selector located in higher position than the final version, and suffered from low selectivity to interference.
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E52a Koln Early prototype

The reason was the presence of the band selector shaft too close to the demodulator in the upper left corner. The BFO signal came in the RF stages creating beats To solve the problem the mechanism has been redesigned placing the band selector in the final position.
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E52a Koln Final prototype

On May 1941 the final prototype, developed at Telefunken Berlin-Zehlendorf, was ready but it was not yet fully tested.
A small pre-series of about 20 units, built for the test has revealed still significant defects. None receiver of these pre-series has survived the war.
One of these defects was not effective functioning of the BFO
In these early versions the demodulator had three valves instead of two. This can be seen from the design of the frame that can accommodate three valves.
In the final version of the BFO module was further shielded with a flap that covers the two valves. At the mechanical motorized unit was implemented a soft stop mechanism to prevent frequency misalignment. The distance between the plates of the variable capacitors has been doubled with a consequent increase of the plate surfaces. The mechanics of the band switch has been strengthened.The malfunction of the BFO has not been completely eliminated but the urgency of production not allowed to extension the development phase.
According to Telefunken document F7 Dr. Be/J. (Be = Bechmann) dated 1 October 1941 were ordered by Luftwaffe 3230 E52 Koln.
On February 1942, the personnel responsible for production in Sachsenwerk Radeberg, near Dresden, where E 52 Koln was produced on a large scale, were trained at Telefunken in Bertin-Zehlendorf.
At Sachsenwer Radeber in the building "E" of the 2nd floor where disposed: in the main wing of the building the production lines and the west wing of the test facilities.Production began on July 1942 not with E52a version, but with a small number of E52a-1 (Ln 21000-4) in parallel with a series of E52b-1. Both series have used the common parts with the exception of the motor unit and the IF bandwidth variable filter.
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E52a Koln Final prototype

The manufacture was not up to speed until the beginning of 1943.
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Assembly factory Sachsenwerk Radeberg

While the modules were made in several different electronics industries around all the Occupied Third Reich zones in order to relocate production in many different sites so that the bombardment of one factory does not stop the entire production: The power supply was made at Telefunken-Gera╠łtewerk Posen, Poland while the IF module, with its quartz filter, was made at Telefunken-Fertigung in Paris.The mechanical tuning module was produced at Telefunken Berlin-Zehlendorf.
After the factory testing each unit of production was examined by Luftwaffe official. The acceptance of the equipment was marked with "BAL" timbre (Bauaufsicht Luftwaffe=Luftwaffe Inspection Office)
The shipping of the produced units from the manufacturer to the Luftwaffe was the prerequisite for the payment of the receivers.
It has also to consider the strict operational secrecy that prevailed at that time in Sachsenwerk-Radeberg. For example, the plant manager of production of the short wave transmitter 10 WSC had no knowledge about the production of the corresponding receiver Ukw.Ee in the same factory until the end of the war!
Soviet troops arrived in Radeberg 8 May 1945, shortly after German troops, mainly SS-Panzergrenadiere, had left the city.
In the weeks before there had been heavy fighting between Lomnitz, Leppersdorf Kleinröhrsdorf and Bautzen with very high losses even in the civilian population. At Radeberg war was ended and Sachsenwerk was now in the hands of Soviet troops. The factory was almost intact even if the production was stopped. Foreign workers and their families returned to their homes. The dormitory Sachsenwerk became a camp for displaced eastern. Stalin ordered the expropriation of large landholdings and vast land not used by Sachsenwerk industry were expropriated and given to new settlers and farmers.
In October 1945, the Soviet military administration decide the seizure of all industrial equipments used for the military production. Between fall 1945 and spring 1946 Sachsenwerk was completely dismantled. Machinery, equipment, materials and documents were transferred to the Soviet Union. For this work, it was used the workforce present in Radeberg. With the end of the operation, there was no longer in service workforce. In Saxony in June 1946 the Communist Party had expropriated more than 9000 companies becoming "public property".
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Scachsenwerk factory dismantled after the war

  • Sachsenwerk Radeberg

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Scachsenwerk Radeberg Factory on Satellite Map

On first August 1946 factory was re-opened under Soviet supervision with the name SAG, "Soviet Corporation”. In October 1946 the Soviet Factory Director gave the order to assemblies 20 E52 Koln using the still remaining parts.
USSR industry learned it' s design and produced the following receivers, inspired by E52: Krot and Krot-M, R-251, R-252 "Dolina" (Valley), R-310 "Dozor" and R-309.
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USSR Radio R310 "Dozor"

A small number of units were ordered by Sweden government, together with Dr Rohde und Dr Schwarz quarts-clock during the war. They were paid for but not delivered, until late 1948-50; the receivers were reconditioned by Rhode ans Schwartz and "demilitarized" in silver-grey color. Some of these receivers were used for time synchronization between universities that were close to or had own optical observatories. All equipments became obsolete around 1955-56 when time signals were sent on upper part of FM-band (approx. 105MHz) from a central source.
In the next picture taken in 50s is showed a professional listening station that use
E52a Koln receivers
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Radio Station in the ealry 50s

It is estimated that about 2400 to 2600 Koln receivers had been built between the start of series production in 1942/43 from the end of production on April 1945 but only about only less than 500 are still in existence Only less than 300 are in perfectly serviceable and cautiously guarded by some of the more fortunate connoisseurs of German radio equipment. These relatively few precious sets miraculously survived the war, as well as the succeeding mania of senseless destruction of 'former-enemy radio equipment' as ordered by some of the Allied military commanders after the German capitulation. However, what does appear to have been definitely lost, unfortunately, are many details of an impressive research that stood at the beginning of the highly advanced technology that made it all possible.

In order to reduce interference susceptibility on overseas HF radiotelephone circuits, the Deutsche Reichspost (precursor of today's Deutsche Telekom) had already inaugurated SSB traffic between Berlin and New York in 1931, as proposed by Dr. W. Runge of the firm Telefunken. For this purpose, after the war, on late 1950, Siemens & Halske have introduced the EB1/3A SSB/ISB adapter "Käthe” for Telefunken E52 "Köln" receiver.
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E52b Koln with SSB/ISB adapter EB1/3A "Käthe"

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E52b Koln with SSB/ISB adapter EB1/3A "Käthe"

Technology
The receiver is an advanced single superheterodyne with two RF stages, mixer/local oscillator, three IF stages, detector/BFO/AF amplifier and an output stage for headphones.
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The antenna, with input impedance about 150 ohm, is followed by a double-tuned band-pass filter that drives the first RF amplifier. Next comes another double-tuned band-pass filter, feeding the second RF amplifier. Then follows a single tuned circuit and the mixer that converts the incoming signal to the 1 MHz IF. The mixer also receives the signal from the local oscillator. The five preselector circuits and the local oscillator are tuned by the sections of a six-gang variable capacitor.
Directly following the mixer is a fixed tuned IF filter with no fewer than six circuits. Next comes the first IF amplifier, a crystal filter with continuously variable bandwidth, the second IF amplifier, again a crystal filter, the third IF amplifier and a single tuned circuit that feeds the detector circuit for audio and AGC voltage. When used for reception of telegraphy the signal from the beat frequency oscillator (BFO) is also fed to the detector. The oscillator frequency can be adjusted from the front panel; but it can also be controlled by a quartz crystal on 1000.9kHz. When crystal controlled, the oscillator also provides calibration signals. Finally, an audio amplifier brings the signal up to headphone level. We will now take a closer look at the details of the E52 receiver. The tuning has a coarse scale and a fine scale projected from a micro photo disc with very high resolution and accuracy. The glass discs were individually calibrated for each receiver. A spare disc, produced for the replacement or the remote control unit, has been stored at the Telefunken head quarter at Berlin Zehlendorf . All the spare disk stored, with the technical documentation, has been destroyed or lost during the Allied bombing raid on 1945. The remote control unit not went into production. A built-in spare lamp can be brought into operation by turning the slotted screw below the ground glass screen should the operating lamp fail The oscillator has very accurate temperature compensation and thus high stability. Frequency coverage is 1.5 to 25 Mhz in five bands, the sensitivity for AM 3 - 5 uV, CW wide 1.0 uV and CW narrow 0.3 uV for 5 V output. Mirror frequency damping is at least 50000 and the IF damping is better than 100000 at 1.5 MHz. The stability is better than 30x 10E-6/degree C, that is 30 Hz/MHz/degree C for a free running oscillator! The performances are comparable with the famous monstrous US military tube receiver R390A produced from 50’s to 80’s that was used also for the NASA Apollo program.

Variants:
Type Ln-number Remarks
-E52a 21000 Motorized tuning
-E52b 21000-1 Manual tuning
-E52c 21000-2 Dust proof special type, like E52a. Never produced
-E52d 21000-3 Simplified, motorized, special tuning, recorder output. Never Produced
-E52a-1 21000-4 Simplified, motorized tuning.On E52a-1versions with glass scale number > 1200, and white numbers, has been introduced the same improvements of E52b versions, in particular to the adoption of a trimmer capacitors for high end bands scale recalibration.
-E52b-1 21000-5 Simplified, manual tuning
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E52b-2 21000-6 Simplified, manual tuning, unified scale.Produced after September 1944.Scale number > 2000
-E52b-3 21000-7 Simplified, special manual tuning, unified scale.
-E52a-2 21000-8 Simplified, motorized tuning, unified scale. Produced after September 1944. Additional switch for C290
-E52b-4 21000-9 Simplified, manual tuning, unified scale,steel capacitors. Different diversity connector
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Steel Capacitor found on flea market

Remarks:                    Ln =  Luftnachrichtentruppe (RLMs ”catalogue number”)
                                  21000        =  receiver number, E52 x-n resp n  =  model

The a-2 has been the latest. version introduced. This version was introduced in September 1944. The production of this version seems to be due to the request to make quick changes of frequency (frequency hopping)
The latest versions produced: a-2, b-3 and b-4 contain further elements of simplification due to the increasing production difficulties such as coils dl second RF stage are unshielded. The identifications b-3 b-4 are found only in the technical RLM but have never been shown on the nameplate of the receiver. The probable reason is to hide the simplifications introduced.
Identification Plate
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Identification plate

The identification plate contains the followings information :
  • version (a, a-1, b-1, etc..)
  • Gerat Nr : Equipment number
  • Werk Nr. :Serial number
  • Anforderz. :Ln number
Equipment number begins with 124, followed by the number 420, which characterizes the E 52, and a letter such as "A", which refers to the basic version for example E52a or "B" stands for execution. B ", the non-motorized
Serial number is also printed generally on the internal right side of the left tube compartment door.
The first three digits are referred the production block. The units produced for each block are significantly less than 1000
435 : a version (“Grundversion”) and some a-1 version
436 : a-1 with improvements introduced on ‘b’ versions
462 : b-1
463: b-1 e b-2
464 : b-2
467 : b-1
258: a-1 and b1
65 : b3 (Ln 21000-7)

It is possible that in autumn 1944, some batches have, instead of a plate with a stamp that with the age has disappeared.
The Ln number is the General Catalog Number Rl.M. For the E52 receiver is LN-21000 Koln-X where X varies in function of he number of variants introduced (see table above).
Motorized Tuning Versions
An interesting feature of the tuning module of the type E52a receiver, so revolutionary at the time, is the frequency memory with its 'power-assisted' automatic tuning. Four different frequencies can be stored, irrespective of band. When calling up a certain frequency, within seconds one of the electric motors turns the band-selector switch to the correct position, while the other motor adjusts the tuning capacitors until the selected frequency is obtained. In spite of the entirely mechanical principles on which the system is based, the accuracy is highly convincing. Even today and being accustomed to digital memories one cannot help feeling impressed by the accuracy of the system.
This functionality is described in detail in a specific page of this site
Remote Control Unit
The following picture show the prototypes of the E52 Koln remote control unit.
This projet was cancelled.
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On the left-hand side the master unit is shown (Fernsteuergeber). It was supposed that it should control the Köln slave unit (the centre apparatus) by means of telephone signals. The slave unit (Fernsteuervorsatz) is mounted to the front section of a Köln receiver (of course, the front panel had to be removed firstly). On the right we see the (projected) interface units. Of which, presumably, one unit reached actual trials.
E53 Ulm
Only few hundred of E53b Ln 21001-1 simplified manual tuning version was produced by Telefunken until the end of the war.
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E53b Ulm

This model has to be considered VHF version of the E52 Koln in fact the radio electronic architecture is very similar to E52 Koln
It use 12 valves RV12P2000 plus 2 tubes rectifier RG12D60 and incorporates also FM discriminator.
The frequency coverage is 23,7 to 70 MHz, in five bands, with sensitivity for AM and FM 4 - 18 uV, and CW 1.0 uV.

Bibliography

  • Luft-Boden-Einheitsempfänger E52 Prüfung-Reparatur-Abgleich Teil I: Netzteil, ZF, NF ;Teil II: Mechanik, Optik, HF Conrad H. von Sengbusch DJ2DK, Ulrich Wintzer DL7FZ
  • Luft-Boden-Einheitsempfänger E 53 Teil 1, Kurzbeschreibung und Betriebsvorschrift
  • Luft-Boden-Einheitsempfänger E 53, Gerätehandbuch Teil 2
All the above documents are available at Peter Gierlach, DF3KT website
  • Bo Samuelsson Vintage Radio Website
  • LA8AK's WW2 German radio page
  • Wolfgang-D. Schröer (DL7HZ) Köln E 52 Vorläufer und 'Nachklänge'
  • Telefunken World War II Superheterodyne Receiver E52 ‘Köln’ – Part 1 by Dick Rollema, PA0SE : 08-Aug_Sep 2002 issue of Radio Bygones Magazine
  • Telefunken World War II Superheterodyne Receiver E52 ‘Köln’ – Part 2 by Dick Rollema, PA0SE :10-Oct_Nov 2002 issue of Radio Bygones Magazine