Continuing Nachtfee aircraft display reconstruction with:
Chapter 19 (9 September 2022)
Chapter 20 (12 September 2022)
This page was, for technical reasons, initiated on 4 September 2022
Current status: 12 September
Photo 1: During the summer holidays Hans Goulooze commenced a fine job constructing the stabilised HT power supply which was integrated onto the existing wooden system plate
Photo 2: A quite nice view on the way Hans Goulooze did built-up the various components
Photo 3: Viewing it from a slightly different perspective
Photo 5: Considering it from the opposite (top) site
Photo 6: Considering it, from what later will constitute the upper side perspective
Photo 8: Here the circuit plate (board) has to be mounted
Photo 9: Hans is determining the position of the bottom wooden sliding-rail
Our concern mainly is, that the board should be easily mounted and demounted by a single person.
Photo 10: The sliding rail being filled-up by means of a wooden strip as to ease correct horizontal mounting
(19) (9 September 2022)
Adjusting the two nuts against one-another as to allow smooth turning of the common screw-threat; as the centre screw has to be kept when the mounting-plate being detached from the current mounting
Please, imagine: that the two nuts, each one pressed in their wooden frames.
The Challenge to assure that both srew-nuts being positioned against one another that the screw rotates through up to the (stress) fixing point
The colours of the connections correspond with the colours of the according jacks.
For this moment we have waited about a year
(current consumption of 1A is telling us that only the new circuitry being operated; 25.1 V constitutes our substitute aircraft battery supply (Bordspannung).
Of course, it all is a reconstruction of the kind of display once used in, with Nachtfee, equipped aircraft.
However, the developed circuitry was engendered in step-by-step process.
Our line of thought: using, when appropriate wartime German valves en techniques then known.
Some adaptations were necessary, because we lacked some essential dust-core components, and we had to utilise existing transformers instead.
However, our advantage it was a thrilling process which resulted in a success.
The only essential difference compared to wartime techniques - is the application of a Philips/Fluke PM 5193 synthesizer.
That we use this versatile instrument originates from our early learning days after our Nachtfee Consol arrived on 12 November 2011.
The stability of the internal quartz crystal was so poor, that it wasn't even possible to keep the time-base more or less stable for 5 à 10 seconds!
For it, we implemented, successfully a Rb-frequency standard allowing now values of: 10-10 and 10-11. Even the PM 5193 at 15 kHz isn't stable enough, only because we operate it at 500 Hz, thus divided by a factor of 30; making it sufficient stable. During the wartime days, the displacement of a Ju 88S was about 600 km/h (166,6 m/s) and therefore necessitating constant distance re-adjustments.
In someway or another this line drawing must show how once the aircraft Nachtfee display must have looked like
This information was derived after interrogation of German personnel.
You may now better understand why we have constructed it the way we did; please forget the two controls for focus and brightness, which we have, for practical reasons, positioned above- instead of below the CRT display.
On the far left-hand side the FuG 25a transponder
down in the centre two interfaces.
The left-hand one converts the IFF (or EGON) necessary for painting the Nachtfee order signal at the LB2 CRT.
The right-hand interface is just operating in the opposite direction, as it feeds the aircraft time-base 0° signal towards the Nachtfee Consol on the ground.
This photo is quite self-explaining
This is the actual reason why we had to mount the circuit plate the way we did.
On the right we notice the staircase entrance to our basement.
The basement facilitate: a workshop and valves storage including various bits and pieces.
(20) (12 September 2022)
YouTube film impressions
Film 00116: I am pointing at the far right-hand side on the HT power-supply providing 2.5 kV, of which is, actually, remaining 2 kV at the deflection cylinder of the circular LB 2 crt (due to the application of zener diodes). Hans Goulooze created, during summer time, a soundly constructed stabilised HT power-supply, which facilitates ca. 280 V. For it we adapted, for practical reasons, post-war valve types. The system concept, like in wartime days, relies also upon the 24/25 V dc "Bordspannung" which historically also obeyed to multiples of n x 6.3 V. Between the cathode of the series regulator valve and its according filament we measure, ca 280 V difference. Far too much voltage and the normal solution is, to employ an additional, insulated towards ground, filament transformer windings. Also the used EF 80, as its cathode lays here at + 90 V against ground; thus an extra separated filament transformer winding is necessary. The matching 220 V (230) transformer was at hand (Hans Goulooze's gift) and we therefore did it this way.
Film 00119: Is showing the results of just over a year lasting commitments, in (re)constructing a LB 2 circular crt display with all the background technologies. Not claiming that it once did look like this; but at least we know that they operated a LB 2 circular crt - like is maintained in our Nachtfee Console as a 'control screen'. We encountered, already from the beginning (hysteresis) that distortion of the to be operated 'sine and cosine' signals necessary for the two deflection Yokes systems, were limiting the projection of a soundly painted 'circle' at the LB 2 screen. Theoretically, there is no way around to compensate these kind of distortions. Again a brain wave - why not tuning each deflection Yoke section in 'series resonance'? Some of you might remember - that distortion is being caused by the existence of some kind of harmonics - odd or even or combinations. By tuning the deflection-coils in series resonance (all systems are relying on sine-wave signals), we eliminate to a great extent the amount of harmonics. And it truly works! The advantage is that due to the implementation of a series capacitor that we were able to implement (inject) a small (variable) dc current (ca. 3 mA) by which means we can adjust the circle inside the engraved markers. Not understood then (2011 .. 2012/2013), was that the Nachtfee system could only be operated when there is a second system-timing reference available. I came - after a quite long process of various, imaginable, considerations - to the conclusion that the 0° phase air-system pulse had to be supplemented to the existing signal chain (aircraft - ground station, vice versa). About 2016 someone most kindly - she managed to pass onto me a copy of the report made in June - September/October, 1945, in New York. Life would have been quite more easy wouldn't they (US Navy) being so '...' (not interested) to publish (September/October 1945) the description of the aircraft display schematically, at a level of: C14 is connected on to R17 ... Finishing with noticing that the schematic was no-longer is existing. (They lost it within 3 months!) Therefore, we ourselves had to re-invent everything! Nevertheless, this document: Technical Report No. 520-45 October 1945 (kept at NARA); at least it was confirming that my own considerations were correct - that a timing reference pulse (signal) was additionally added towards the ground sent via the FuG 25a transponder as well. This additional timing information allows the system to adjust the signal phase such - that it is being displayed at the LB 2 crt screen inside the 'pathfinder' aircraft just in time (correctly).
Film 00120x: (AOB: 'x' only indicates that about the last film minute had been deleted) Viewing now the Nachtfee Console 'on the ground' again, operating within the current (re)constructed LB 2 display. Shown is also - that Nachtfee basically relies upon a coherent system, where the main timing signal parameters originating from a single signal source, whatever their phase difference is, like additionally between the ground station via the aircraft transponder arriving again at the video-input of the Nachtfee Console. The aircraft time-base reference signal shown at the Nachtfee control screen, have to be constantly adapted to the actual separating distance between the ground-station and the pathfinder aircraft (the German pathfinder aircraft type Ju88S could have displaced itself with about 166.6 m/s max.) and demanded constant ground consideration. Because both systems relied upon comparison between both 0° instances of the - Nachtfee Console as well as the aircraft time-base source - we can now take only into account the common 0° situation displayed on the Nachtfee Control LB 2 screen (please notice: that the signal distance upwards is (approx.) equal to the signal displacement downwards). Generally the aircraft 0° phase pulse is adjusted also at about 0°; because there are some minor time-delays due to the electronic circuitries and minor deviations had to be systematically taken into account. One thing can be proved, is, that adjusting precisely at a given fixed 0° point, it is ascertained that the order signal vector equals the given order at both screens - in casu - on the Nachtfee Console as well as at the aircraft LB 2 screen. Please bear in mind: that 500 Hz prf constitutes a range of 600 km; in radar terms, the signal has to pass the trajectory twice (up - down), the radar range becomes: 300 km.
To be continued in due course
By Arthur O. Bauer