Nachtfee Repair II


A new survey: repairing our

Nachtfee Console


We are suffering a circuitry malfunction,

with an increasing failure occurrence.

About, say, a year ago we encountered a failure, where apparently

the deflection circuitry failed.

After some measurements, I came to the conclusion that a valve circuitry failed apparently.

I changed valve No. 9 and the circuitry started to operate again. However,

after some time, think of ca, two months; and the same failure occurred again.

The failure frequency was increasing, and since a few weeks, it occurs nearly every next day.


Page initiated on 30 November 2023

Current status:  29 June 2024.



Part 1

Part 2

Part 3    (since 23 December 2023)

Part 4    (since 29 December 2023)

Part 5    (since 6 January 2024)

Part 6    (since 14 January 2024)

Part 7    (since 20 January 2024)

Part 7a (since 24 January 2024)

Part 8    (since 3 February 2024)

Part 9    (since 10 February 2024)

Part 10 (since 23 February 2024)

Part 11 (since 23 March 2024)

Part 12 (since 30 March 2024)

Part 13 (since 26 May 2024)

Part 14 (since 29 June 2024)








Nachtfee repair II schematic 2a


Please consider the valve numbered 9 up on the far left-hand side; by the way type RV12P2000

When the deflection-fault is occurring, the anode voltage does drop to ca. 16 V; whereas when the circuitry operates correctly we measure, say 160 à 165 V dc.

The circuit is a bit strange as the anode resistor connected to a filter circuit is 300 kΩ.

In my perception - valve 9 is acting as a kind of current-load only. The two (band-filter) coils being tuned at the PRF of the entire system of 500 Hz = 2 ms.


However, the situation in which Nachtfee is being displayed, does not allow sophisticated measurements

I therefore have decided to move the Nachtfee console to a place where comprehensive measurements can be accomplished.



Albeit that this place is currently not available, as it is being used during Secret Communications 4 is open to the public

Its purpose to us is only to show you as to how measurement gear can easily be placed for our experimental repair/fault searching.

But, Deo volente, Secret Communications will close at the end of the day of 17 December 2023.

Paul and Marc promised me to clear this table before they will return homewards.

This photo being copied from a Survey of about 2015/2016 as to allow you to get an impression - as to how we would like to explore the free space available. 



Here formerly, our Nachtfee system had been on display since ac. 2012

But, for the time being, we decided to move our Nachtfee Console system, including its moveable table, to a suitable site inside our museum premises. 



This should be a suitable place for future repair of our Nachtfee Console

The adjacent exhibition gear annex, will be moved elsewhere on the very day, our Secret Communications 4 will have come to its closure after 1700 hours 17 December 2023.

Down in the background you will see a collection of electronic meters.

All should be operated equally as had been accomplished the last 10 years.



Please ignore the adjacent gear, which will be removed at the end of the day of 17 December 2023



Another necessary change has to be re-mounting our 25 V dc power supply

The reason is, that this Power-supply magnetic or electronics, is interfering with the circuitry of our Nachtfee acryl substitute.

Causing the time-base line being blurred.

After quite due considerations we have decided to reshuffle it a bit towards the background.



Hans Goulooze is planning for an additional wooden frame where the 25 V power supply will be mounted where now the 2.3 kV power-supply stands



Finally viewing as to how I imagine the repair set-up should be accomplished


Our aim, Deo volente, is - to let the entire Nachtfee system operate again - as it did so in the passed 12 years, since.



YouTube Films:


Film 00135:    Today 30 November 2023, we would like to explain to you why a repair of our Nachtfee Console and system has become necessary.  The main reason is, that the horizontal and according circular time-base lines are increasingly showing problems. In the beginning we discovered at least which circuitry is mal functioning. First we thought, that a RV12P2000 valve did strike; as after a replacement all operated satisfactory and reliably. But after some time the failure intervals were increasing. Currently repairing a circuit and during the day remained functioning, but when being operated for the next occasion (day) it is striking again.    The circuitry is extremely difficult to access; I (AOB) have decided that a comprehensive approach is necessary; but the rather limited space does not allow tracing the failure. I therefore choose to move the entire Nachtfee Console rig mounted on a moveable table. 

Film 00136:    This is showing you how difficult the circuitry can be accessed. We need space for example placing several electronic meters at the same time, by which means we can monitor what component is behaving faulty.  May safe "Deo" us from a faulty filter unit, that the filters being built-in such that these being hardly accessible.


Film 00137:    Again film recorded on 30 November 2023.    Our regular Nachtfee set-up has been cleared, and the movable table incorporating also auxiliary gear such as signal- and generators being move to a space well fit for longer lasting repair and tests. The unit on the right-hand side is the Gemse IFF receiver.    At the end of the day of the 17th December 2023, the first table should be cleared from the gear mounted on it. So that we can start with our repair Survey soon.


Chapter 2

AOB: Today we are succeeding with our repair survey.

We have now been able to resettle our moveable Nachtfee Console

at a setting where we are able to measure the failing Nachtfee Console electrically (electronically) 





Part (3)   (since 23 December 2023)

Proceeding on: 21 December 2023


On Thursday 21 December 2023, we finally have been able to gain space again for continuing our Nachtfee repair Survey II

Shown on the left-hand oscilloscope screen are the 2 ms transmitted transmission pulses.

Albeit, the minor energy being fed onto a BNC miniature 50 Ω dummy-load.



We switched the system on again, as was encountered many time before, the Console operated seemingly perfect!

However, as we encountered this phenomenon too often before, I didn't trusted the circuitry, any way.


Let us first take a closer look at the main points of our failures.


Let us first consider the actual available potentials of A and B against ground.


My though - about the 300 kΩ resistor between the top the (band-)filter coil (tuned at 500 Hz) and the anode of valve 9 is a curious device. It might more-or-less function as a kind of current source as the 'parallel-tuned' anode current is passing through this band-filter section.


Consider place also the next photo


The meter on the left-hand side is showing the actual voltage of about 320 V on the above schematic designated with an A

The right-hand meter is measuring the dc voltage at potential B

A 300 kΩ series resistor is interconnecting the potentials A and B

Whereas the right-hand meter is showing the actual voltage measured at the the lower end of a filter coil

Please notice: that as the anode circuitry is being fed via a series-resistor of 300 kΩ the actual ohmic load at point B can therefore not be neglected.

B measured the voltage at the anode of valve 9 (RV 12 P 2000)

It was noticed that connecting the two meters is resulting in amplitude drops on both CRT screens (the circular LB 2 and the dual beam HRP2 2/100 crts.)

Therefore, I use the x 10 times reduced meter sensitivity and herewith increasing the voltage range by a factor of 10; though also reducing the current-load. Therefore, both meters possessing now a maximum voltage range of 3 kV (compared with the formerly 300V).

Though, the left-hand meter being set at a full scale of 1 kV whereas the right-hand meter being set at 300 V range.

It operated for several hours perfectly, but at a certain moment (after a few hours) the circuitry started to malfunction again.

And, both voltage dropped to:

At the anode of Rö 9 we measured instead of say 160 V but in malfunctioning ca. 16 volts

However, also the voltage at the left-hand meter dropped considerably!

This is indicating that we likely are dealing with a current rise within Valve (9) (RV 12P2000).

Two possibilities are open: NF 4 secondary winding provides no signal onto the grid 1 of Valve 9. Whether due to a failing signal input of transformer NF 4 is not yet determined with certainty.   



Changing the RV 12P2000 did not restore its functioning.

Considering all parameters, I came to the conclusion, that it is not unlikely that the mal-function being caused in the RV12P2000 grid circuitry.

Re-considering the various parameters, I came to the conclusion that the real reason of its failing being the failing signal input provided at pin 5 of the NF 4 transformer.


Here I made a mistake, for which I am not directly to be blamed.


Please compare both the circuitries 12. with 14.

The impression is that it concerns a better circuit-schematic;

but this is an error as it concerns a totally different circuitry section!

The only matter is: that after every Servo/Goniometer they used a selective 500 Hz filter-circuitry; using the same component-types of filter-coils and according R and Cs, though again carrying similar part designations on several occasions!

These filter circuits function quite well, also the variations of the search-coils of the Servo/Goniometers outputs are quite well kept smooth including most of its amplitudes. 


Please consider the Servo/goniometer designated Phase on the left-hand side of the above schematic

On the CRT screen we notice the signal output measured on the 'search-coil' of the Servo/goniometer


My first though was: that this concerned the same circuitry and I considered: might our problem originate from the 'Phase" phase-shifter (dial) circuitry?


 I measured point 3 of the transformer NF 4 and at the anode of valve 8

and measured now:


Oh what a confusing mistake!


We are viewing at two signals one directly derived from the search-coil of the Phase goniometer; the second signal was derived from the anode of this according valve.

However, I discovered that NF 4 being not the component-number of the particular transformer involved, but it concerned a 'type NF 4' which is being operated in several circuitries in our Nachtfee Console!

Thus, the Phase-goniometer is not concerned in our fault-trace procedure.

But, that quite many circuitries being similarly being wired, including the various smoothing filter circuitries!


My conclusion is:

That the failure is originating in our schematic 12.

I suppose that its NF 4 transformer arrangement is causing our frequent, though also sometimes irregular, failures.

It might be that a transformer winding (connection) breaks sometimes down.


This is the actual is the actual situation currently it is clear that accessing will be quite a challenge


I therefore took the next photo allowing a bit more view where the transformer NF 4 is build-in.



Our actual NF 4 transformer is visible in the middle down of this photo

(AOB: please notice the Al box on the right-hand side of our trouble causing NF 4 in the centre;

It most likely also concerns a NF 4 transformer as its in- and outputs are respectively point 3 and 5. Following the wires connected on the pins 5, are exactly bended as the wire connected onto centre Al box.

Therefore I regard both Al boxes concerned being of the type NF 4)

The yellow wires are constituting ground connections.

It is clear that its accessibility, when it has to be removed for repair, might cause quite a problem.

I have added onto the schematic the position-number provided on top of the NF 4 transformer

To my best possible way I have tried to re-solder the wires but also heating up the according transformer wires.

Maybe you recognise a metal strip, which keeps all Al boxes fixed at their places.

When in case of continuing troubles, the screws fixing the latter metal strip is to be accessed only from the left-hand side-wall plate on the far left-hand side of our Nachtfee Console.

NF 4 might point at: NF = low frequency say audio-like designed for 500 Hz operation; transformer type 4.

When we encounter continuing troubles - I could measure the two inductances of the primary and secondary coils; as to get an impression of what these are about.



Let us now consider the brief means how we mixed up the former Nachtfee set-up and the current repair facility:


We prefer to keep the former infrastructure operational, where possible

Therefore the existing 'variac' (Grundig) is kept in operation, as we do with some other cables too.

Its mains voltage output is to be adjusted at the variable 'variac' such that we measure across at the filament of Rö 9 across its filament-contacts 12.6 V ac.



(4(since 29 December 2023)

Hans Goulooze has prepared a simple wooden frame for carrying our HP pulse-generator

We necessitate sharp pulses, for keying our miniature TX mounted just in front of our table just adjacent to our R&S type SMS digital signal generator. This transmitter module mounted inside an Al box is loaded with a miniature BNC 50 Ω resistor.



Let us consider the symbols A, B, D, D used in the foregoing contribution; which equals the foregoing description


When we switched on the Nachtfee-Console today it failed operating.

Quick measuring at the two points designated with E showed that already here the necessary signal was failing.

But at what servo/phase-shifting goniometer is it connected onto?

The letter symbols being identical to the symbols used in the foregoing chapter.


After due consideration I came to the conclusion that it should be the with an E designated failing input signal.


This Servo/goniometer is serving the essential range information. With 'range' we mean the distance between the Nachtfee-ground station and the delay of its signal return.

This value is an essential system parameter, which we need to know quite exactly - how long the Nachtfee Command-Order necessitate to arrive at the signal output of the FuG 25a IFF receiver sent from the the EGON station arrives at the aircraft display screen.

Without knowing the time the Nachtfee Phase controlled signal necessitate to arrive at the Nachtfee aircraft display the system never could have operated accurately.

We are not yet for 100% certain that our current nuisance is actually originating from a failure directly originating from this Servo/Phase-shifting gonio-meter.

I remembered, that when I noticed failures before, that a tiny rotation of the 'Entfernung' Distance Range Gonio-meter is the final failure. Luckily, the sequence of failures are becoming every time more frequent.

But patiently, it demanded as to become certain that this is the true causing failure.

The strange circuitry with the EDD 11 valve is quite curious, as it should supply a 'three phase' 500 Hz signal ( 3 x 120° signal differences).    The manually rotated search-coil is now operating as a gonio-meter allowing phase shifting between 0° and 360°      


The HP pulse generator is fed from a digital signal generator


We necessitate rather sharp pulses, supplied by a 502 Hz or 498 Hz sine-wave source.

There rise-time should be in the range of about 1...2 µs PRF chosen here 502 or 498 Hz.

EGON normally operated at a PRF of 500 Hz. But our Nachtfee PRF is directly derived from a Rb-standard (ca. 10-10 and keeping our signal deviation at 500 Hz controlled. I therefore went over for EGON operation using instead, say 502 or 498 Hz. But could also be taken, say, 504 or 496 Hz ...



We notice two signals being fed onto our BNC mini-dummy-load.


One at 500 Hz constituting our Nachtfee- Order- Command signal with shown moveable the EGON signal, for this occasion set at 502 Hz or 498 Hz

The triggering is locking at, I suppose the 500 Hz Nachtfee Oder-Command and the more fuzzy signal representing the EGON signal, in our occasion differing 2 Hz up or down.


The smaller signal is the one picked-up at the Enfernung Range Gonio-meter search-coil constituting the signal at the line 1 and 2 of the with an E symbolised signal (search-coil output)


The bigger signal is measured at the anode of valve 8 (EF 14)

I have connected the measuring cables such, that when we switch-on the Nachtfee console again, that we instantly can see the input at 'E' and at Rö 8 anode.


Maybe this screen-shot shows the two signals in better proportions



The upper digital synthesiser is being operated in the EGON signal circuitry


The lower digital generator is the R&S type SMS synthesiser.



Viewing the front controls from a different perspective


The EGON signal PRF being adjusted, for this occasion at 498 Hz.



(5(since 6 January 2024)


On 4 January 2024

We continued our Nachtfee Repair II Survey


Today we were able to operate our Nachtfee Console in combination with the simulated aircraft IFF type FuG 25a as well as our new acrylic aircraft display

On top our synthesiser proving our time-base deflection signal constituting a sine-wave; which signal is being split. One direction goes to an interface feeding it pulse signal into the I/O port of our IFF transponder.


  The other route supplies the signal onto an circuitry which provides a sine-wave deflection current for one of the deflection yokes the second signal being a cosine signal feeding its deflection current into the second deflection yoke coil.

The two signals projected accordingly together is providing an first order Lissajous - when the amplitudes being equal it paints a beautiful circle at the circular LB 2 screen; as is visible above.

When you look a bit closely, you might notice at due 'south' pointing pulse.

The pulse pointing at due 'north' constitutes the time-base '0°' pulse-signal which signal should be, in some way or another, be conveyed towards the Nachtfee Console on the ground. As the whole Nachtfee system is handled in the domains of time.

As it is essential in the Nachtfee principle, that one should know exactly what the precise timing status in the aircraft is - as well as having knowledge of the exact range (distance) between the stationary Nachtfee station and the moving aircraft is. The reason is - that signals send in the time-domain travels with the speed of light (c). The PRF of Nachtfee is 500 Hz or each pulse is lasting 2 ms (= 2000 µs). The according wave-length     λ= is 600 km.

But the secondary EGON radar signal has to bridge distance twice - thus consequently the actual system range is becoming 600 / 2 = 300 km.  

This timing reference signal has to pass the way down towards the Nachtfee Console. Now the human brain is entering the system, as the aircraft 0° timing reference has to be translated (interpreted) by the operator's brains and his manual tuning (keeping) of the constantly changing 'Phase' control setting.


Essential to realise is: that the distance aircraft - ground station is equal to the route Nachtfee Consol (ground-station) towards the Aircraft IFF antenna. Albeit, that the aircraft underwent a displacement, per 2 ms pulse-interval of ca 35 cm; which can be neglected. 

 The pleasant result now is - that the Nachtfee signal reflected by means of the aircraft transponder FuG 25a will be displayed on the LB2 control-screen again. Essential is now that the returning Nachtfee signal will be painted or say displayed exactly at the vector at which the Nachtfee Order-pointer is being adjusted. When no order being given the Nachtfee Order pointer being set at 0° or called 'north'. Still constantly controlling the range-offset as the Nachtfee pathfinder travel with a speed  of ca 500 à 600 km per hour. Therefore, the Nachtfee console had to employ two operators, as a single operator hardly can manage all changing parameters accordingly himself.



The actual (real) Command-Order pointer is the small one - pointing at due 'north'


We ignore the larger pointer, as its function is only a mechanical memory operated during operation. 

The range offset (distance compensation) is the control-knob up on the left-hand side, with the visible number 280 km.

The Phase control down on the left-hand side has no scale.

Its adjustment is accomplished by both - rotating the Phase (necessary for controlling the exact arrival of the actual Nachtfee on the aircraft crt). This is accomplished by controlling the aircraft 0° aircraft time-base reference signal.  Controlling it until the 'Nachtfee aircraft timing reference signal is adjusted at ca. 5 minutes past the hour; at least this is our experience.

Thus, the small Order-pointer signal, shown at the above LB 2 control screen, show be controlled and adjusted at an equivalent vector; this is to be accomplished by operating the range off-set control up on the right-hand side.



Monitoring the signals available at the FuG 25a Input/Output pin 9 of the control connector

The tall pulses constitute the Aircraft 0° signal reference; please compare it with photo (27.) at 'due north'.


The pulses in-between the tall ones constitute the actual Nachtfee Order pulses originating from the Nachtfee Console on the ground.

Please notice: the Order pulses aren't equally painted on the CRT screen. Why?

Please bear in mind, that most IFF transmitters in the era 1940-1945 were generated by self-excited transmitters, which suffered from quite some frequency (signal) drift;

the Germans introduced frequency wobbling in their IFF related receivers.  Therefore, the Fug 25a - as well as the Gemse receivers - were provided with small wobbling motors wobbling ca. 2 MHz around the to be expected IFF signal spectrum.

Therefore, the IFF signals being also victim to amplitude variations as well as off periods as the wobbling receiver oscillator can reach (come) outside the receiver bandwidth. But this is lasting only shortly, but periodically. However, human eyes do not notice these fluctuations so much.


Now we caught the situation where the Nachtfee Order signal became temporarily at another instant out-of the capture range of the aircraft wobbling receiver

Harmless, as an human eye isn't much aware of such an incidental phenomenon.  



Here we notice a new phenomenon

EGON (Erstling Gemse Ortung und Navigation)

Maybe not directly well visible, but you might recognise that there apparently is a third signal visible on the CRT screen.



At least the third signal is visible, but its PRF differs only 2 Hz; thus is 498 Hz or set at 502 Hz (The Nachtfee PRF, in our case is derived from a Rb signal-source standard at 10 MHz and synthesised down to 500 Hz.

I hope that the YouTube films made will explain these phenomena better.







The Freya-Polwender switch is visible down at the far right-hand side

It is simple to understand that its function only is to inter-change the two output wires (symmetrically against ground).

As Nachtfee concerned a 'Coherent' signal system by changing the two output wires you also change the signal-phase.

In doing so, for instance the Nachtfee Order-pointer being adjusted at due 'north' that after inter-changing the two output wires, the signal 'blip' due north will jump at due 'south'.



Nachtfee was guiding the 'Pathfinder' aircraft to wards the exact location of dropping their flares.

But a trip towards a target could take quite some time in which only 'now and then' some 'Orders' had to be passed on. In the meantime the "Beobachter" (Navigator) had only to watch the instant where action became necessary.

The entire Nachtfee signal conveyed - nowadays known as a "Payload" - upon the EGON secondary radar signals communicating with the aircraft transponder; in our simulated wartime means represented by a genuine FuG 25a system.

It proves that a YouTube Film is far more informative than a photo series; let us therefore considering the next:



Film 00141:    We first notice the various signals which being provided at the Input/Output test connector pin number 9 of our FuG 25a IFF set up.    The tall, quasi, fixed pulses are representing the 0° aircraft time-base reference pulse. Which is being painted, say, just at "due north'. Actually its left-hand side steep shaped vertical line is the 0° reference pulse (noticed at the aircraft crt). The less taller, but stable pulses, actually representing the Nachtfee 'Order Signal'; albeit not yet 'Phase' corrected at the Nachtfee Console 'Phase' control. The Fug 25a transponder receiver is fit with a frequency wobbling motor, by which means a spectrum range of ca. 2 MHz being wobbled at a rate of, I suppose, say 12 to 15 Hz. Just too fast for noticing what is occurring. However, photo's being taken mechanically or digitally, but in both systems a 'shutter-time' being involved and this is emphasising the wobbling fluctuations. When you interrupt the YouTube film you might notice that the visible two pulses in the middle between the three 0° reference pulse do not being equal in amplitude; this is being caused by the nature of the wobbling/scanning nature of the receiver frequency; constantly tuning up- and down a particular frequency spectrum. The moving pulses first from the right to the left (498 Hz) constituting the EGON signals; at some instant I change the EGON signal PRF from 498 Hz to 502 Hz (all versus the fixed Nachtfee 500 Hz PRF) and consequently the EGON pulses are now moving into an opposite direction, as our oscilloscope is triggering at the invariable 500 Hz Nachtfee signal PRF.  As we have been told already that the receiver is searching around a centre frequency - also the EGON pulses being fluctuated (when you interupt the film, now and then, you will better understand the occurrences). Shown is also the in/output connector, in particular its pin number 9.     


Let us now focus our attention upon the control screen (the circular deflected LB 2 crt) inside our Nachtfee Console.

Film 00143:    Viewing the LB 2 circular control screen.    The stronger pulse 'a few minutes past the hour, is constituting the Nachtfee time-base reference signal; but is to be controlled by a 'Phase' control, see (28.). This signal is directly derived from the 0° signal inside the aircraft electronics and sent simultaneously with the regular EGON secondary radar (IFF) signals towards the ground station. The weak pulses due 'south' constituting the genuine Nachtfee 'Order' signals returning from the simulated aircraft IFF; having bridged the trajectory twice (Nachtfee → FuG 25a → Gemse RX → Nachtfee). At a certain instant I switched the signal from due 'south' to due 'north'. This is accomplished by simply operating the switch designated by 'Freya-Polwender' (simply inter-changing the two symmetrical output wires) (see first (33.) and thereafter (34.)) Please watch at about 2 minutes 20 à 25 seconds - where I demonstrate the operation of the 'Freya-Polwender' switch (this phenomenon is only becoming visible, because where you actually are looking at is the signal ones transmitted up to the simulated aircraft transponder FuG 25a and its response returning again to the Gemse RX and then painted at the LB2 control screen again).    I thereafter explain what the effect of operating the Freya-Polwender switch is having at the simulated aircraft display presentation.


Film    00144:    Viewing now in particular what is currently being visible at the LB 2 crt screen of our simulated Nachtfee aircraft display. Up is shown our Signal synthesiser set at 500 Hz constituting our aircraft time-base reference signal; which output is a sine wave with 5 V pp.  Viewing the simulated aircraft 'circular deflected' crt screen. The circularly rotating signal originate from our simulated EGON secondary radar (IFF) system.    Demonstrated is also the response at the crt screen of moving randomly the Nachtfee 'Order' pointer.     The rotating EGON signal firstly set at 498 Hz is set at a separate signal synthesiser at 502 Hz causing an opposite rotation direction.



(6)    (since 14 January 2024)

On 11 January 2024

We switched on our Nachtfee Console and simulated aircraft system.

All functions well; though our system has to be kept control, as long as, we aren't sure that we really traced the failing circuitry.

Last Saturday, 6 January Paul and Marc replaced our artefacts on display again.

Why not showing how the contexts looks like again?


Viewing our Lo70KL40 system again, which had been adopted by the post war Czechoslovak military services as type: Jalta (Yalta)

On the right the grey module constitutes  the genuine power supply



Our telephony display corner

Up we notice the so-called: 10 lines Klappenschrank (Field-exchange) on its far left-hand side the "Wähler-Zusatz"

Allowing connection with a regular telephone exchange



On top the beautifully constructed KWE-a receiver


In my perception one of the best receiver concepts.

From the mechanical and electronic design perspectives; in particular considering its year of concept; of ca. 1936/37.

6 fold tuning capacitor.

Tell me: I have been taught that critical circuitries in RF necessitate a central earth-point, for each RF/HF section.

They really realised it consequently in the beautiful coil turret.

An additional AVC/AGC amplifier stage.

4 IF - Bandwidth selections additionally keeping the smallest IF bandwidth and additionally introducing 3 LF bandwidth selections; the 4th selection is switching over the side-band!

Two quartz controlled BFO frequencies.

The calibration points for each band being compensated for the 900 Hz BFO off-set!

Separate RF and LF control; when operating without AVC/AGC control.

However; the downsides: operating 11 battery valves type RV 2P800.

IF is 250,9 kHz.

Though, due to the lavish implementation of pre-selector stages its "image suppression" is still impressive.

This receiver had been adopted first by the German Army (Heer) and their requirements in the 1930s were among others: mobile battery supply of 2 V and a 90 V anode battery.

Below the open KWE-a (shortwave up to 10.2 MHz) we notice a LWE-a (Longwave) using 8 valves RV 2P800 and had an IF of ca. 60 kHz.



On the far right-hand side the Peiler-Heinrich receiver

Next to the KWE-a/ LWE-a we notice the beautiful E3 HF/DF RX




Based upon an adapted KWE-a receiver, on its right-hand side the according DF-Goniometer designed for the application with 4 Adcock antennae mast

of which two are shown  : one on the left and one on the right-hand side (not visible here)



In front on the left-hand side my: Rarity (Rariteiten) Cabinet, with various sorts of devices



Viewing the German Army communications corner

On the left-hand side our GK IIIb with implemented Tfb 2 carrier telephony'20.htm

On the far right-hand side we just notice the long-medium wave 100 WS.



The 100 WS including its genuine "künstliche Antenna"  (artificial antenna) on top of it



On the left-hand side the forerunner of the EZS 2  "Blind-landing" beacon transmitter; on the right the long-range beacon transmitter type AS 4



The radar search corner

The heavy receiver is type Korfu  (S-Band), but introduced about late 1944

In the middle with the coils on to of it: EO 281

On the far right-hand side: the Naxos receiver/display



The temporarily created Radione Corner



At the left-hand corner we notice the 20 W type S 406/S 1936 sub-marine transmitter

Next to it the T9K39a receiver

On the right of it the 200 W transmitter type AS 59



The AS 59, adjacent to it on top the Siemens Abwehr receiver type R IV

Next to it the Schwabenland Luftwaffe Type:  Ln 21021

Manual: D.(Luft) T. 4415

Right of it the Lo6K39

next to it the long-wave version type




Next to it the Lorenz VLF receiver EO 509/III



From left to the right:










(7)   (since 20 January 2024)

On 18 January 2024

We continued our repair project VI



After some difficulties I was able to improve the performance between the Nachtfee signal source and the output of the FuG 25a transponder "In- and Output" control at pin 9 of the central test connector

Both receivers employed in Nachtfee as well as generally with the German IFF systems were relying upon signal wobbling as to catch signals which had a bit drifted away from a given centre frequency.

One would expect that this wobbling is hampering the application of Nachtfee or IFF generally.

This, actually is not the case, as the human eye combined with the human "grey cells" do not notice such a phenomenon.

Hans Jucker some decade ago published a paper:


AOB: what likely is also not visible on a video film, I have tried to take a range of photos, and then afterwards I selected the ones that is showing the typical sequence of the wobbling of signal data.

It is simply causing amplitude variation at various instances, due to the camera exposure-time and the incident of triggering the camera-shutter versus the 500 Hz PRF of the Nachtfee data.


Please compare this photo with the foregoing one

When the centre of the wobbling curve equals the given signal frequency, than their are only minor variations visible.

And this photo is giving a good idea of what actually occurs.

The case, however when the signal has drifted towards end of the wobbling spectrum, then you will encounter a that often the signal is painted on the screen only ½ of a cycle time.



The test-connector of the FuG 25a transponder is well visible about the centre of the set

At a single pin number 9 we encounter a central control-point at which we can pick-up the FuG 25a receiver output which is thereafter fed onto the FuG 25a transmitter; but at this very pin 9 we also inject the Nachtfee display time-base pulse just when the 500 Hz time-base signal passes through 0°. This instance is detected and after processing inside an interface and being injected at the same signal as we are picking-up our Nachtfee Order signal.

The clue was just to adapt the input circuits of the two, nearly equal interfaces; and it performs over-all quite well.

Hence, connector pin number 9 is really acting as a single in- and output terminal.



The new acrylic Nachtfee display is showing:

At say 0° (due north) the Nachtfee timing reference signal.

The signal just at, say, ca. 183° is representing the Nachtfee Order signal given at the Order Compass at the Nachtfee Console.

However, the a bit fuzzy  simulated signal - actually is the IFF EGON signal send by the simulated ground station. This signal once followed the trajectory of a guided Pathfinder aircraft.

During wartime days, EGON relied upon 500 Hz PRF.

However, the time-base quartz reference are having a rather poor performance and were even for us useless.

Therefore Marc Simons and Peter Kievits, provided an interface unit which handled the 10 MHz sine-wave in such a way, that we have two derived signals from our Rubidium-frequency standard giving 15,000 Hz and at will also 500 Hz.

As some quartz channels were apparently defect, I inject the 15000 Hz sine-wave signal at the g1 of the oscillator valve RV 12P2000.

Providing now a very stable signal - but not of, say 502, 504 ... or 498 or 496 ... Hz as Nachtfee had been designed for but, an un-variable 500 Hz after dividing by a factor 30.

So I am forced to interchange the PRF's Nachtfee is relying upon 500 Hz and the IFF channel is fed from a 502 Hz or say 498 Hz.

However, as to enhance the understanding I have lowered the frequency difference to 1 Hz only (currently set at 501 Hz).

We have already noticed that even small PRF difference of a single Hz do not at all hamper communication / understanding.

As the Nachtfee order system is "coherent"  and EGON signal are non-coherent. So the order signal at is remaining steady at long intervals and EGON never remains at a single vector instance but always rotates fast or slowly, it doesn't matter at all.    



The only signal that quasi ran away is the non-coherent EGON signal differing only a single Hz

Please compare this photo with the foregoing photo (53.)



The next EGON signal being presented at, say, ca, 300°

It is impossible to predict when triggering the camera shutter at what instant an EGON signal being painted at the crt screen. That the instant becomes quite fuzzy is due to the remaining opening of the shutter timing



Viewing at the new setup

Hans constructed a small wooden frame as to reorganise the set up of the two main power supplies

Below the 24 V dc and up the 2.3 kV HT as well as the 12 V ac for the LB 2 filaments.



The new set up, reaching its completion



The new setup looks quite sound

The EGON signal is visible about 270°

The visible pulse at due north is indicating the 0° point of the sine-wave signal generated in the above Philips PM 5193 synthesiser.



Viewing again the new setup under repair and reconstruction



Newly noticing the effect of wobbling the receiver-band up to ca. 2 MHz

That amplitudes vary is quite clear.

What does not vary are the vertical poles, which originate from the signal generator 500 Hz and after differentiation in the the most right-hand interface.



That some pulses are lacking is also due to the phenomenon caused by the multiple PRF during the opening of our camera shutter



Another example of the effects caused by receiver-frequency wobbling



Please compare this photo with the three foregoing

We have noticed now enough examples of the influence of signal wobbling, whereas the overall effects being hardly visible by the human eyes and the according brain responses.



Actually not directly being aware of it: was the quite critical metallurgical status of the receiver front-panel after its storage for ca. 3 months in our depot



It looks better now after my treatment with "Kontakt 88" oil (a mixture of natural- and artificial oil)



Viewing it finally from a different perspective; apparently the oil is not yet being rubbed away fully

But it is evident, that the main damage / danger is being wiped away



(7a(since 24 January 2024)

Let us bear in mind some of the foregoing photo series:






Let us next consider the video film recorded on the 23rd January 2024


YouTube Film

Film 00149:    Viewing first the video recording of the running signal flow, picked-up at the in- output test pin-connector 9. Firstly considering the pole- like pulses originating from the simulated aircraft system.  These pulse being trigger by the instance when the sine-wave signal is passing through 0°. This is the core signal on which the entire Nachtfee system is relying. Essential in the whole system is (was) that the Nachtfee Console on the ground necessitates actual information what the hypothetical 0° status of the aircraft is.  As the Nachtfee signal transfer is relying upon signal phases in the domains of time. A simple example: Nachtfee is fully dependable of delayed signals. But the to be guided aircraft is, they hoped for, travelling from the controlling station. Consequently, a signal phase shift is also arriving every instance later at the aircraft system. But it was necessary to delay (or speed-up) some orders. The time-base system inside a Pathfinder aircraft has to be defined. But range is constantly increasing and this phenomenon has to be cooped with. Therefore, the Nachtfee Console on the ground necessitate a reference send by the time-base system inside the aircraft.    The Nachtfee system was a kind of "payload" signal on the guiding EGON (=IFF) system. The Nachtfee signal received by the aircraft FuG 25a transponder was taped and conveyed onto the display crt. But it was after reception again being re-transmitted towards the Nachtfee Console. Factually the Nachtfee Consol possessed also a, what I designated "Range offset". This control compensating for ranges between 0 km and 300 km. Making it simple: it can be adjusted such, that offset can be tuned until the Nachtfee Order pointer is exactly indicating the pulse on the CRT similarly with that is facing the mechanical Nachtfee Order pointer. So far so good. Extensive experiment has shown that the Nachtfee aircraft reference signal has to be adjusted some degrees passed the hour (0°) think of ca. 5 minutes passed the hour.  The Aircraft reference pulse is operating within the Nachtfee system being non-coherent. Curiously now when tuning the Phase Control knob, only the received Nachtfee time-base reference pulse (signal) is moving along the LB 2 control screen in the Nachtfee control.



(8)   (since 3 February 2024)


Today (1st February 2024) my first aim was to improve the presentation at the Nachtfee control crt type LB 2, as on earlier photos the presentation was more sound then it currently does.

My first thought went in the direction of a resistor which could have changed, its value, over the 80 years.

However, Siemens wartime resistors rarely suffer from such nuisance; and this apparently remains to be yet true.


Please notice the two adjustable 2 trimmers below the circular LB 2 crt

One video portion being fed onto the LB 2 g1 (Wehnelt cylinder with its own mutual conductance  value/ Steilheit) and the other video signal being fed onto the deflection cylinder with its lower mutual conductance Steilheit as well.

The art is: to find the optimal video-signal balance.


These are the two trimmers shown in the above schematic with a tuning range op 20 - 90 pF

Some time ago we suffered problems with an instable soldering contact in the LB 2 base, maybe even before that I have tried to find out what the influence was of these two trimmers.

However, now I approached them and noticed their influence op the signal presentation at the LB 2 crt screen.


After Hans Goulooze kept a mirror in front of the Nachtfee Console, so that I was able to tune these trimmers as to provide the most sound signal presentation (alignment).


The art of adjusting is to find a compromise between signal amplitude and the signal shape

The pulse due south is the returning Nachtfee signal passing from the ground system via the EGON/IFF transponder FuG 25a in the simulated aircraft and received in the Gemse receiver on the ground again. 



The blue arrow represents the Nachtfee signal send from the Nachtfee Console towards the Freya/EGON guiding station

From there two signals being conveyed by 'free space' towards a German Pathfinder aircraft (mainly type Ju88S) and received by their EGON/IFF transponder type FuG 25a.

At its test-pin number 9 the signal being split one triggers the transponder transmitter and the second route goes towards the Nachtfee display in the aircraft.

But, it is essential that the Nachtfee station on the ground gets the exact information when the sine-wave time-base inside the simulated aircraft passes through 0°.  Here represented by the yellow arrow which after ground reception being also conveyed onto the Nachtfee Console LB 2 crt screen.  This is the 'TB' signal in the foregoing photo being the pulse presented at about 'five minutes passed the hour'.

This fundamental signal should be kept during operation at this vector - as the aircraft is more or less constantly moving away from the ground station towards the area where flares had to be dropped.

 Most system parameters being linked electronically - but the yellow arrow has constantly to be controlled (readjusted) for two factors first is the range off-set, but secondly the time-base-reference arriving from the aircraft has to be controlled such that the stronger signal being kept at the vector 'five minutes passed the our.

It is evident, that this can only be managed by two operators.

One controlling the range off-set, the other one keeping the aircraft time-base signal at the vector of say 'five or seven minutes past the hour'.

The 'Phase control-knob' is having an essential function: as it delays the signal such that the next signal pulse (500 times per second) arrives just at the correct instant at the simulated Nachtfee LB 2 crt screen.  

This will later be explained differently, as well.


Unexpectedly I discovered - a new aspect:


Apparently I focused to bring in-line the two stronger pulses (on the far left and right end)

Maybe not well visible:

this concerns a real dual beam crt possessing two independent systems. (please consider also the above schematic)

The time lines being derived from the same sine-wave signal as is the Nachtfee order/Command signal, but one crt system is painting the line from: left - to - right, whereas the second system writes the same sine-wave: from the right - to - the left.

And, one vertical signal is deflected upwards and the second is painted down-wards (only inter-changing the deflection plates of the dual-beam crt).

This guarantees that, as is shown at this photo (two pulses aligned back-to-back correctly at the screen centre).

In my perception a quite smart and essential achievement.

Please bear in mind - that the vertically painted video signals being fed onto both crt deflection plates (systems) simultaneously. 

My fault had been before:- that I neglected this provision and focused upon: - to adjust the LB 2 signal presentation equally as the Nachtfee order / Command pointer has been set.

It became apparent to me, that there existed always a discrepancy between range off-sets  - reproducing the returning Nachtfee order signal by means of the range off-set. What, time and again, occurred was: that the Phase control was causing a fuzzy vector setting at 'five à seven minutes passed the hour or even beyond'.  




Let us please: - first take a look at this photo - without  additional explanations

The 10 cm  plan crt screen is of a dual-beam type manufactured by AEG  (HRP 2/100/1,5A).

The essential alignment is to tune the range off-set scale here set at just over 240 km (visible due to the illuminated scale window)

The smaller crt LB 2 is showing: - at due south - the genuine Nachtfee order / Command signal retuning from the simulated aircraft EGON / IFF transponder type FuG 25a.

The signal tuned here about 7 minutes over the hour is the Nachtfee aircraft timing reference actually generated when the sine-wave time-base signal passes through 0°.

Its position can be circularly moving on the time-line by means of the 'Phase control knob' just down left of the Order/Command Compass.

Intriguing always is:- that only the non-coherent simulated aircraft time-base reference signal is moving, whereas the coherent Nachtfee signal remains fixed (some slight irregular interactions occur but this has to do with inaccuracy of the 'Phase' goniometer (0° ... 360° phase shifting); I suppose.

The small pointer is pointing just at due south, and is equally painted at the LB 2 control screen; its correct position being adjusted by means of the Range off-set control (also left from the Compass but up)


Let us now digest the various interactions by means of the white arrow-lines.


Please compare this photo with the foregoing photo

Both being the same photographs, but the above one showing the controls and their interactions

In my perception it is quite 'self-explaining'. A second not well


A second not well understood phenomenon encountered:


We noticed during the simulated operations of the system always two (order/Command) signals presented:

one possessing a higher amplitude and one with a bit smaller and weaker amplitude.

After considerations the smaller amplitude signal left of the more bright signal is the actual Nachtfee order / Command signal.

The stronger signal amplitude originates from the very fact: that we are lacking sufficient insulation (separation) between the receiver and transmitter antenna circuits.

Of course, the pulse at due north is the Nachtfee time-base reference pulse - which is also fed onto FuG 25a test-pin 9 and therefore also is acting as video signal after processing painted at the LB 2 crt screen of our simulated aircraft display construction. 

The fuzzy signal chain being painted, is representing  the simulated EGON signal, which's PRF differs only a single Hz.

Nachtfee is relying, in our context, upon a PRF of 500 Hz whereas EGON, for this occasion, being operated at 499 Hz; the exposure time of our camera is causing broadening of the signal.

Please bear in mind: that Nachtfee operates 'coherent' and EGON in the Nachtfee context is behaving - non-coherent.


(9)   (since 10 February 2024)


On 8th and 9th February 2024


I made first a series of YouTube films of which I only could use two samples.

The reason was, that our Panasonic video camera, was playing several times quite mad. Starting as usually but after a while the auto-focus was striking; causing totally blurring images!


For the fist time, I would like to introduce an English language (EN) version as usually

but the second film has been made in German language (DE);

and repeating this.

Because on the European continent, the German speaking population are in the majority of ca. just not yet 100 million inhabitants (Germany, Austria, Switzerland and in the border regions of France and Belgium not neglecting Northern Italy).

But it is an experiment, indeed.

Whether this will prove to make sense, is to be determined later.

This contribution is the successor of what started last week:

I would like also to add two brief contributions on the visibility of the Nachtfee order shown on the simulated aircraft display

in conjunction with the EGON (IFF) signals.

As you might remember, that EGON is the main system which should guide a Pathfinder aircraft over a proposed target and thus is a secondary radar system.

Nachtfee is a kind of pay-load added onto this existing guiding system.

The frequency difference of the EGON (secondary radar/IFF) and Nachtfee was, at choice: + 2, 4, 6 ... Hz and - 2, 4, 6 ... Hz.

For our demonstration I choose 1 Hz as this shows even more clearly that even such a minor PRF difference do not causing any kind of information interference!

As already noticed in the introduction of today: that I will try to contribute also a German language YouTube version of it; my advantage is that I am bi-lingual, thus for it isn't difficult to accomplish.   


Please notice: the text I speak - is not read from paper, but originate directly out of my mind; it therefore might differ some.

The main reason is: - that my brain does function differently in every language in which I communicate; thus do so my thoughts.



00153 Film EN:    Today explaining the demonstration of last week in which we used a photographic series. The reason is, the valid finding of the correct alignment adjustment at the dual beam crt type     HRP 2 /100/1,5A. It was found that always doubtful alignment were commenced in the adjustment op the aircraft-time-base-reference-pulse at the Nachtfee control screen.  Explained are: the three main controlled, actually by means of phase-shifting gonio-meters; as well as their interactions.


00154 Film DE:    Gezeigt wird erst wie man korrekt der Entfernung Nachtfee Bodensystem zum Flugzeug hin Rechnung tragen kann; einen Vorgang die dauernd nachgeregelt werden muss, da das Nachtfee-Flugzeug sich mit bis zu 500 à 600 km pro Stunde van der Nachtfee/Egon Bodenstelle entfernt.


00161 Film EN:    This time our attention is focussing on the simulated aircraft display (using by the way a genuine wartime crt which equally had been used in the Nachtfee systems. The main aim today is to show you that the Nachtfee order signal painted at the simulated aircraft system is not being hampered by the second signal differing only a single or two Hz; whether above or below 500 Hz does not matter. Explaining that EGON and IFF do not differ much and that EGON is also a secondary radar system; which guides the German Pathfinder aircraft towards a fixed target. Nachtfee aircraft were only Pathfinder aircraft, like were British OBOE Pathfinder such as Mosquitos.


00162 Film DE:    Gezeigt wird heute (9. Februar 2024) Unser Ziel ist zu zeigen, dass das Egon Signal (Sekundär-Radar) und dass das Nachtfee-Kommando Signal sich gegenseitig nicht stören, und ein Kommando Signal wie auch immer korrekt sichtbar bleibt auch noch bei PRF Frequenzunterschiede von nur ein Hz.


(10)   (since 23 February 2024)                     


On 22 February 2024

Hans Goulooze showed me a connector which he had obtained somewhere and that should match onto the video-output connected at the rear end  of our Gemse receivers; as the one in use typically had been meant for matching at a frame-mounting.


We have in a crate some genuine German wartime coaxial cable samples.

After some due considerations we decided that the typical German coaxial cables consisting inside of ceramic-breeds. Their colour often is light blue, and consisting of PVC.


In the cable bundle centre we notice the coaxial connector components


The new video output cable is visible


The internal breeds allow for some flexibility

It was, however, only maintained just there where cables were mounted in a fixed manner.

I am not entirely certain that the operated just such type of coaxial cable; but this is what we possess.

I checked the old video output versus the new coaxial cable output.

There was no much difference visible at the oscilloscope.



We were bound by both the true cable diameter and the hole in the rear side of the coaxial connector

Which in our case do match perfectly. 


The coaxial cable is completely integrated in our Nachtfee 14 pins List connector

The two blue wires constitute the Nachtfee Order output signal, which is symmetrical against ground.



(11)   (since 23 March 2024)

Today (21 March 2024) a quite brief notice according: 


Today only a single photograph:

Measured across the dummy-load - we notice that the pulse-width of the IFF transponder signal being just over 500 ns; not too bad isn't it; measured at ca 157 MHz.



(12)  (since 30 March 2024)


Today 28 March 2024

Our Nachtfee Console is still being under test, as to be sure that we really have cured the nuisance of our failing crt deflection failures.


However, the top-cover plate, had been removed some years ago - why not remounting it appropriately again, and keeping the test set-up operational for a while?


Please remember the foregoing state of affairs before we continued today


Firstly, I have 're-inserted' the genuine top-cover plate

Of course, I had first to disconnect the various cable connections.


Luckily, I kept the according screws and three quite heavy hand-grips, at a safe storage

I had forgotten why the plywood plate was; simply as to allow it remaining without sufficient mounting.

Thus I removed it because it no-longer is making sense.


Two hand-grips in front and the third one  on the right off the cable-access

Deo volente, we should at least keep the entire Nachtfee repair/control set-up on its current place, where it should be better accessible, when something goes nevertheless wrong; but fully operational.

Likely for a few months to come.


(13)   (since 26 May 2024)


On 24 May 2024

We continued today our DMG5K survey

Our Nachtfee repair II setup, is following a particular philosophy:

Of course, repairing defects (say mall-functioning, or intermitting defects).

I decided today to re-mound the rear cover-plate again; which might have been removed for more than ten years (being kept off or de-mounted)

As we always encountered sooner or later some nuisances which forced us to access the Nachtfee console from inside  again.

Following the line of our current approach - I would like to replace the rear cover-plate and operating Nachtfee for some time to come.

You might have got the impression that we haven't accessed Nachtfee for quite some time, but this isn't actually the case; as we operated the set every time we were engaged in our Museum.

The only defect encountered was a failing Oltronix power supply, but this device I did purchase in the early 1970s.

I took a closer look inside, and noticed a blown small blue colour selenium rectifier bridge type B30C300. (Siemens)

A difficulty: I don't know where I keep the schematic, and the bridge is telling us: +/-

But which of the two output leads are representing + and which on the - (pole)?

So, as to continue I implemented an old Philips power-supply, but this one provides only 30 V dc maximally, whereas the Oltronix device supplies 40 V.



Viewing our Nachtfee apparatus from the rear left-hand side of Nachtfee Consol


Viewing the cover plate from a different perspective


The small square Al box is representing our TX, gating the Nachtfee Order (Command) signal as well as EGON signal

Hanging on the left-hand side is the simulating pulse-modulator of the EGON signal.

Please notice at the upper display: the the EGON PRF being set at: 501 Hz; whereas Nachtfee operates at a PRF of 500 Hz.


The signal pointing at, say, due south is representing the Nachtfee Order signal and the smaller signal painted at say 25 minutes passed the our is representing the EGON signal

Please, bear always in mind: that within the Nachtfee system the Nachtfee order signals being coherent and the EGON signals are not coherent and therefore rotating visually though: is not interfering with Nachtfee Command message.


The left-hand side neon-indicator informs us that the thermostatic controlled oven is operating

I could have disconnected the oven - as it does not have a function in our set-up (relying on the Rb-controlled generator visible on top of our Nachtfee Consol;

but is providing an understanding that genuinely there is a quartz controlled oven involved.



The 'thermostat' neon-indicator  being 'off' is indicating that its 60° C has been reached temporarily


The front-panel of our Nachtfee Consol under test again

Please notice the red (lamp) indicator is glowing red.

This indicates that quartz channel '1' has been selected;

but quartz channel '1' is having a defect quartz, and by means of the twisted (pink) wires we feed in stead a 15,000 Hz sine-wave signal which is derived from our Rb-generator on top of our Nachtfee Console housing.

Why 15,000 Hz?

Because the Nachtfee quartz-oven is providing at channel '5' 15,000 Hz

As each quartz is differing 60 Hz to one-another (+ and -), hence: the quartz fit at channel 1 should have been: 14760 Hz.

Maybe some of you might recollect: that the system PRF is 500 Hz (considering in our case 'the quartz frequency provided by channel 5') is 15000 Hz

A PRF of 500 Hz is provided by dividing 15,000 Hz : 500 Hz a division of '30'    

This analogue division process is being accomplished by means of so-called: regenerative division; which relies upon sine-wave signals.


Let us re-consider the next drawing - I once did make about 2012


The quartz-stage with its analogue division chain is visible top-left including with the proceeding analogue division stages.

Copied from my: Nachtfee-evolution and conclusion chapter.


The next photo once had been taken in December 2011

Please notice the: 'up left-hand side quartz' (vibration mode being longitudinal) 


The Pt-mercury thermometer is visible on the right-hand side of the quartz and the heating elements being mounted at the lid-cover on the far right-hand side On


(14)   (since 29 June 2024)

On 26 June I decided to replace the the Nachtfee configuration at its genuine place in the museum again.


Today we moved the rolling Nachtfee console configuration to its former genuine place

Making room for a new endeavour: getting our Tonschreiber-b apparatus operating again.


Our Nachtfee Console configuration stood here for more than a decade; and returned, simulated, operational again


  The weak signal at 'due South' represents the simulated ground signal returning via the simulated FuG 25a IFF transponder


The signal pointing at say 4 minutes passed the hour represents the simulated Nachtfee aircraft-time-base reference signal, which represents the 0° of the painted Lissajous figure at the simulated aircraft display

One should expect it should be 0° degrees, but apparently we have to take into account some delay being caused in the various electronic circuits.


Maybe you like the same photo but reproduced a bit less bright


Sun-light is reflecting in the camera lens


Let us experience, whether our Nachtfee console continues to operate again



By Arthur O. Bauer