German Ground Stations
There are many German radios that were used in ground stations. They are too numerous to discus in this short series. There are four receivers that seem to be easily found and are sought after by collectors. These were discussed in great detail in the articles by Dick Rollema. These are the Tornister Empfanger b. the short-wave receiver LO 6 K 39a, the KwEa and the E 52 Koln. I will include briefly some information on three sets.
 Torn Eb Early Version |
Tornister Empfanger B Torn Eb Probably the most commonly encountered German radio is the Tornister empfanger b set. We will use the original German designation of the receiver we are going to discuss now. The photograph shows a front view of the set. You see that the set consists of two units above each other. The cabinets meant to be carried on the back of a soldier-that house the units are called "Tornister' in German. Actually in the photograph you see two half "Tornisters", one housing the receiver and the other the power supply. Empfanger" is the German word for receiver. And the letter 'b' in the designation simply indicates which receiver. Mostly the designator was shortened to "Torn E b" and that is what we will use. The Torn E b was created around 1935/36. It was in general use with the German Signal Corps, but also at higher army staffs, police and traffic control authorities. It was a popular set, produced in great numbers and one of the few sets that found their way to amateur service in Europe in post-war stations. It is a tuned radio frequency (t.r.f.) set with four filament type tubes that were run from a 2 volt battery at 0.2 A. each. So the whole radio consumed about 0.8 A. from the battery. The anode current came from a 90 V. dry battery at a consumption of about 12 Ma. It was also possible to generate the h.t. from the 2 V. battery via a vibrator unit and that is what you see in photograph . The vibrator unit is on the bottom shelf of the lower cabinet. Still another possibility was to run the whole set from a 12 volt automobile battery, also with a vibrator for the HT. The set covers the frequency band 100-6970 kHz in eight ranges. The actual coverage of
each sub-band is as follows: Photographs show the inside of the set. The receiver has two r.f. amplifiers. a regenerative detector and an audio output stage, producing sufficient power to drive two sets of headphones. There are three tuned circuits of which the variable tuning capacitors are ganged. We also find three sets of eight coils, one set for each subband. The coils with their associated fixed and trimmer capacitors are housed in a coil turret that can be clearly seen in the photograph . This picture shows several of the features that we mentioned in the previous section. The coil turret is of cast alloy and contains completely screened compartments for each coil. The contacts are supported on cylindrical ceramic bars. The three gang tuning capacitor is also completely screened. You see the shaft bearing on the backside of the capacitor at the lower left. You also notice the bases of the four tubes. The two r.f.s and the detector tube are at the left, the a.f. tube at the right. The tubes disappear completely in the tube holders. They can be withdrawn by means of the circular knobs that are part of the moulded tube base. The two r.f. stages and the detector stage are also completely screened. The extensive screening and de-coupling leads to an extremely stable set with no trace of undesired feedback between stages. Let us again take a look at the front . The big knob at the lower centre controls the coil turret. Immediately above it the selected sub-bands number is shown in a little window. Left and right of centre you see windows that display a table; this gives the frequency that corresponds to the reading of the fine tuning dial that revolves with the tuning capacitor, seen at the right. The table lists the frequency in increments of 5 dial divisions. But for a finer reading we can extrapolate between these increments; in a fourth window, immediately above the one that shows the sub-band number, we read how many kilohertz correspond to one dial division. For sub-band 1 this is 0.8 kHz, as you may be able to read from the photograph. The knob called "Ruckkoppl" at top right controls the regeneration of the detector stage, number 55 in the circuit diagram. Any of you who have used a t.r.f. set know that the joy or misery you derive from it is determined in a major part by the action of the regeneration control. The set should slide smoothly into oscillation, without thumb or backlash, that is to say the detector should start and stop oscillation at the same position of the control. These desirable features are dependent upon a number of factors in the circuit, as any of you old-timers can testify. But the German designers of t.r.f. sets certainly knew the secret of making a fine regeneration control. The one on the Torn E b, or any German t.r.f. set for that matter, is a pure joy to use. Fine control is assisted even more by a slow motion drive on the regeneration capacitor! The knob with the crank turns the tuning capacitor via a 1:19 slow motion drive. This operates with great precision and with a smooth feel. Nevertheless it was at this point that the author had some criticism on the receiver; at the high end of the frequency band covered by the set near 7 MHz, one revolution of the tuning control changes the frequency by I some 200 kHz and this is too much for easy tuning of s.s.b. signals.This criticism is quite unfair, of course, as at the time the receiver was developed s.s.b. was unknown, at least for military applications. Still I found a way of fine tuning the set; as with most t.r.f. sets at high frequencies the regeneration control pulled the receiver tuning somewhat and this could be used as fine control. The control marked "Lautst" is the gain control. It varies the screen grid voltage of both r.f. amplifier tubes. This works very well and avoids the possibility of overloading the detector. Top centre we find the antenna trimmer with screw driver adjustment. It is marked 20 in the circuit diagram. For telegraphy an audio filter, tuned at 900 Hz, can be brought into the circuit by means of the switch "Tonsieb." The filter consists of a parallel tuned circuit with coil 62 and capacitor 63. It is very effective on c.w. |
 Torn Eb Late Version |
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 Torn Eb Late Version |
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 Torn Eb and Accessory Chest |
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 Torn Eb Vibrator PSU |
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 Torn Eb Late Version, Internal View |
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 Torn Eb Late Version, Internal View |
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 Torn Eb Late Version, Internal View |
 Torn Eb Wire Antenna |
Top left on the front panel we find a voltmeter. It reads the filament Voltage. Not only is the meter calibrated so that the proper voltage of 2 V. can be read, the correct voltage reading is also indicated by a red marker! By pushing the button on the meter front the instrument reads the h.t., that should be 90 V. and the correct value is again indicated by a coloured marker on the meter face, this time in blue. In 1943, due to the shortage of war materials, this meter was eliminated and replaced by a metal plate.Finally we find on the front panel an on/off switch that controls the filament current, a plug for the power cable and sockets for two sets of headphones. And of course two big and easy to use terminals for antenna and ground. |
As already mentioned, although the design is now over forty years old, the set still performs remarkably. As to be expected the receiver is at its best on c.w. Especially on the 500 kHz marine band it leaves nothing to be desired. But also on the long wave and medium wave broadcast band many more stations were copied than on a modern run of the mill superhet. Quality of the audio is rather limited, but then the set was certainly not meant for music. Selectivity is excellent. In fact on the long and medium wave bands the regeneration control should not be advanced too far. otherwise serious top cut is experienced.
Also on the short wave bands c.w. is received very well. S.s.b. can be resolved too, but tuning gets a bit tricky there, as already mentioned. Cross-and inter-modulation forms no problem. Even in Europe's extremely crowded forty meter band. with its many intruding strong broadcast stations, amateur c.w. signals can be easily copied at night, a test that many modern superhet's fail. The forty meter band is not within the range of the set according to the official specs, as it does not tune beyond 6970 kHz. Nevertheless, in practice some 30 or 40 kHz of the 7 MHz amateur band is in fact covered.
One is struck by the quiet operation of this t.r.f. set. The input noise is just noticeable on a quiet band. And the background level is steady, no doubt caused by the fact that there is no a.g.c. As a well-known Dutch radio expert stated before WW II: "automatic gain control moves the fading from the signal to the background."
The set is rather small, 36.5 cm wide, 24.5 cm high and 22 cm deep. This is for the receiver alone. Together with the battery and accessories 'Tornister" height is 46 cm. But the weight of the complete unit is surprising, 24 kg (52.9 lbs.).1 The complete set consists of the receiver and the accessory case, headphones and antenna and ground leads. In addition one of the three power sources must be used. The original dry cells are not made any more but any dry cell battery that produces 90 volts can be used. The receivers turn up very often, the accessory chests are rare items.
 KWE.a Receiver and PSU |
Receiver KWE-a or LWE-a This is a master piece which has put a technical standard that, in my opinion, was the world's best battery tube powered communication receiver for that freq. range; if you imagine that is was designed (I suppose) 1936-1938. Not only the mechanical construction, but the circuit design as well were outstanding (advanced). Look for example the design of the IF stages with the band width selection control and/or the separate AVC (AGR) amplifier among many other things. This technical effort is in my opinion quite under valued, from the technical point of view it isn't important that an item (artefact) is too expensive to be produced compared to similar Allied artefacts. Regenerative receivers were an exception (I mean super-regenerative, not straight forward receivers, because the TornE-b and/or Lo 6 K 39 were very good, although no super heterodyne), these were used only for small portable sets But the British used this same principle for the B-set of the WS 19 as well. The major difference between receiver standards from Europe and the US were for the latter that they were using tubes extensively (quantity) which, caused by economical factors, wasn't possible in Europe. US communication receivers often used twice the number of tubes as these were utilised in Germany, Holland and Britain. An other important factor which is often neglected is the fact that the Germans were very well orientated on what was going on in the US and many US articles and publications were discussed by them. Probably because so many German scientist were immigrated to the US and some still had links to Germany kept alive. |
 LWE.a Receiver |
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 LWE.a Receiver Internal View |
 MWE-c Radio Receive |
MWE-c Radio
Receiver |
 MWE-c Radio Receive & Home Made PSU |
 E52 KOLN Receiver |
E 52 b "Koln" Some of the communication equipment and related pieces of gear, like radar, were called after well known German towns. The E 52 is an example of this, because 'Koln' is the name of a famous German town, in English speaking countries known as Cologne. We will use both E 52 and Koln when referring to the receiver we are going to discuss now. There can be no doubt that the E 52 is the ultimate of German receiver design of WW II days. It is another Telefunken design and became available around 1943. The instruction manual that PAOAOB put to my disposal for writing this article carries the date August 1943. The book says the E 52 I was meant for short wave communications in the army and for governmental organisations. |
You get a first impression from it by looking at the two hinging lids that are lifted
to show some of the gadgets under them when they are normally closed. You probably notice
the clean layout of the front panel and the functional shape of the controls. And that was
done in the days that "ergonomics' was an unknown word.
The dimensions of the radio are 24.1 cm high, 44.6 cm wide and 36.9 cm deep. Its mass is a
massive 42.8 kg (94 lbs.). The set can be run from 110-230 V. a.c., from which 60-96 watts
are consumed, or from a 12 V. battery. A vibrator power supply is built in.
There are five frequency ranges, as follows:
( Range I ) 1.5-3 MHz, white scale on the dial.
( Range II ) 3-6 MHz, red scale.
( Range III ) 6-10 MHz, yellow scale.
( Range IV ) 10-17.6 MHz, blue scale.
( Range V ) 17.6-25 MHz, green scale.
The ranges are selected by the oblong control to the left of the indication 'FrequenzeI.nstellung" (frequency adjustment). The frequency the radio is tuned to can be read from the semicircular dial. To avoid reading the wrong scale the frequency ranges are tabulated to the left of the dial and the table also shows the colour of the scale to be read.
A dial like this only provides limited capability to read the exact frequency. Obviously the engineers who were responsible for the design of the E 52 didn't think this good enough and they added a projection system to display the frequency with great resolution. To achieve this the shaft of the tuning capacitor carries a glass disc on which the calibration for each frequency range has been deposited by photographic means. like on a microfilm. A small lamp illuminates the disc from behind and the frequency the radio is tuned to is projected by means of a lens system onto a ground glass screen that you see above the semicircular dial in photograph 12.
As only the figures that belong to the selected frequency range are displayed the reading is unambiguous. In this ingenious way a 'dial" is achieved with an effective length of several meters. The glass discs were individually calibrated for each receiver! A spare disc is included as standard. If the lamp fails the projection system can no longer be used. No problem, the designers already provided a built-in spare lamp and it can be brought into operation by turning the slotted screw you see below the ground glass screen.
These lamps are rather unusual as the filament is off-centred from the middle of the bulb. This makes it almost impossible to obtain one nowadays. But a determined collector is not to be deterred by such a simple fact. An Austrian collector of German W.W.II equipment gave an order to a factory to manufacture a couple of hundred of these special light bulbs. And so he and his fellow collectors can go ahead for many years to come with their Kolns. At what price we will not mention.
The E 52 was made in several models. The one you see in the photographs is in the possession of PAAOB and is the most sophisticated model, designated E 52 a. This variety has the possibility to reselect four different frequencies that can subsequently be recalled by motor drive of both per-selector and fine tuning. The frequencies are indicated by different symbols you see on the table to the right of the dial. The frequencies that are pre-selected are entered in this table by pencil.The frequency actually selected is displayed by its symbol in the little circular window above the table.
The motor driven system operates marvellously. A striking demonstration of it was given by Arthur Bauer. He tuned an s.s.b. station in on one of the amateur bands. This was 'stored" as one of the pre-selected frequencies. He then started the selector mechanism upon which the motors rotated the range selector through all five ranges. The same happened with the tuning capacitor. When finally the stored "channel" reappeared the s.s.b. station could be read with out any re-tuning! And that for a design from a time when S.S.B. was unheard of for mobile communications.
The receiver has been so designed that one type of tube can be used in all stages. The tube is the miniature pentode RV12P2000 we encountered before in the Lo 6 K 39 a and ten of them are used in all. Only the rectifier tubes in the power supply are of a different type. All tubes can be reached by lifting the two lids at the front top of the receiver. This is shown in more detail in photograph 13, and there you see how PAAOB's hand has just retracted one of the tubes by means of a special tool that is screwed into the bottom of the tube. In photograph 12 some of the tubes have this grip fitted and some do not. You also notice that the tubes disappear completely in their holders.
The set is constructed completely in modular form as we would call it nowadays. All connections are made with plugs and sockets as can be clearly seen.The connections between the modules are made through a "mother-board" in modern terminology. Some of the wiring on this motherboard closely resembles printed circuit wiring. It was not made in the way we know it now but it certainly used a similar technique. Nothing new under the sun!
The coil turret used in the prior three previous sets is not used in the E 52, probably it was too difficult to split it over different modules. Instead band-switches are employed. The switch decks can be found in different modules and the same goes for the sections of the capacitor gang. A nice mechanical interface problem.
But it's getting time to take a look at the electrical line up of the K8ln. Fig. 9 snows it in the form of a block schematic diagram. The mixer is preceded by two radio frequency amplifying stages and five tuned circuits. The sixth section of the six-gang variable tuning ca~acitor tunes the local oscillator. As in most German receivers the input is protected by a neon bulb. Link coupling is used in the double tuned band-pass filters preceding the first and second r.f. amplifiers. The oscillator signal is inductively coupled into the cathode circuit of the mixer tube.
The intermediate frequency is 1 MHz and that, together with the five tuned circuits in the r.f. part, provides excellent suppression of the image response. It is specified as at least 1:50000, which works out as 94 dB. At which frequency this applies is not stated so we must assume it is never less than the stated value. The mixer is followed by a fixed tuned band-pass filter at 1 MHz with no less than six tuned circuits. it is followed by the first i.f. amplifier. The tube drives a quartz crystal filter with continuously variable bandwidth.
This system was explained in Part I of this article so we will say nothing more about it here. A second i.f. amplifier follows and another crystal filter section. Then comes the final i.f. amplifier that drives the detector via a single tuned circuit at 1 MHz. It may be interesting to quote what the specification of the E 52 states about the i.f. selectivity: The bandwidth is continuously variable between 0.2 and 10 kHz. Further details are given in the following table:
| Attenuation De-Tuning | Bandwidth Wide | Bandwidth Narrow |
| 3 dB | 5 kHz | 0.2 kHz |
| 40 dB | 10 kHz | 1 kHz |
| 60 dB | 13kHz | 2 kHz |
Not bad for an almost forty year old design, don't you think? The b.f.o. is continuously variable. But when the b.f.o. control is moved in-to one of its end positions a quartz crystal is switched into the circuit and the B.F.O. is then crystal controlled at a frequency of 1000.9 Khz, thereby causing a beat note of 900 Hz with the lOGO kHz if. The detector tube drives the final a.f. amplifier that gives output for headphones.
An extra winding on the output transformer that is in series with the cathode circuit provides negative feedback. At the beginning of this article we mentioned that the designers were compelled to use one type of tube for all stages of a receiver, which fact must have caused them many headaches. The detector stage of the E 52 is a good example of the unconventional circuitry they had to resort to.
The actual circuit of the detector stage in the Koln is very complicated. The final i.f. amplifier drives the detector via a tuned circuit with L and C2. The anode voltage for the tube is fed to a tap on the coil and is de-coupled by Cl. The suppresser grid of the tube, together with the cathode, functions as the diode for the i.f. signal. This is fed to the suppresser grid via C3. R1 is the load resistor over which the audio voltage is developed. This is fed to the control grid via blocking capacitor C6. The tube now acts as an audio frequency amplifier. Because the cathode is grounded the tube receives its proper negative grid bias voltage from a negative supply via R2. The screen grid is the anode for the a2.
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