Nachtfee-Aircraft-Display-Reconstruction

A new Survey

Among Rudolf Staritz's inheritance,

I discovered a circular deflection units fitted for a LB 12, circular cathode-ray-tube CRT.

More or less similar kind of display unit was built in the Nachtfee Console.

 

Page initiated 9 December 2021

Current status: 7 January 2022

Part 1

Part 2

Part 3    (29 December 2021)

Part 4    (7 January 2022)

LB 2 circular integrated within the accompanied deflection mounting

 

My first consideration was the application of a similar control-screen presentation within the Nachtfee main console.

 

Comparison between both presentation displays are quite apparent

The latter display had once been photographed on the Nachtfee console.

(one signal constituting the EGON signal which returned via the FuG 25a transponder and the second one representing the actual signal phase of the TB reference inside the simulated aircraft)

Which one represents the TB reference can only be determined - by operating the "Phase" control which only responds on "non-coherent" signals.

Please consider our YouTube film explaining this aspect  Film 00086:

Considering that the entire Nachtfee Survey did start with: Radar News 19 (notice last page)

 

Let us bear in mind the: Adjustable Airborne Presentation Unit

Some of you will imagine what our future aims are.

Our aim this time is: - to try to imitate a display module which - more or less - is looking similarly, to what is drawn above.

 

We may consider, that the presentation presented within the Nachtfee Console, should equal the one employed within the Aircraft Display unit.

 

But, most likely - as this display originating from Rudi's collection, it will not originate from another Nachtfee console - but from a regular German airborne (short range) radar presentation.

This perception proved to be valid, as the Nachtfee LB 2 presentation operated with a deflection yoke of ca 1 H - whereas our new LB2 display deflection yoke had only a 50 mH inductance. We may consider that it once had operated at a rate of ca. 2900 Hz, whereas Nachtfee's PRF is 500 Hz.

Our first thought is: - why not letting it operate at a PRF of 3000 Hz (exactly 6 times 500 Hz).

Consequently: only once time within 6 periods (spot-rotation) the Nachtfee video signal-pulse will be present, thus reducing the displayed video density.

Optionally 2000 HZ would be an option too. 

Which situation is most efficient is to be determined during this Survey.

 

This constitutes an example which we would like to employ more or less equally (The CRT used in this configuration differs a bit from our LB 2 type)

Ho is to be connected onto ground; and the two dual (left and right - up and down deflection-yokes are representing the: x an y axis)

Our first aim is: painting on the fluorescent screen - a first-order Lissajous between the space between the inner and outer cylinders on the CRT screen.

The essential pre-condition hereby are:  that the deflection fields being rectangular to-one-another and that there exists a phase-difference angle of 90.

90 can easily being accomplished by simple employing according ladder-network arrangements.

Our preliminary perception is: - to supply some sine-wave energy such the the exist between the two grouped coils there is maintained a phase difference of 90 degrees.

 

Dick Zijlmans was so kind to bring and supply us a Philips power amplifier of 15 W (max), constituting (stereo) 800 Ω   and 8 /16 Ω.  leaving to us enough deflection power for our proposed experiments.

 

Hans made a quite nice mechanical arrangement for our next experiments.

 

The schematic of the our deflection power amplifier; please notice - that all signals dealt with are sine-waves

A stereo amplifier.

The necessary deflection energy isn't yet known, as we definitely have to cope with non adequate deflection-yoke self-inductance;

and because all is in an experimental stage, it is very convenient to possess sufficient (variable) deflection energy.

We tend to suppose, after some 'back of an envelope' calculations, that 800 Ω might be a good choice.

 

Hans Goulooze built a sound experimental set-up

The gear-wheel allows deviating the true deflection axis; a provision for us not of significance.

 

Hans built a rather nice experimental testing board, albeit simply constructed of interconnecting wires

The power supply in the background will, Deo volente, supply our 1 to 2 kV HT. (as id once did in the first year of our Nachtfee starting experiments 2011 .. ca. 2012)

 

In front left-hand side one of the three 90 phase-shifting ladder networks (500 Hz - 1000 Hz and 3000 Hz)

We have investigated whether it would be possible to get access  to the deflection yoke inside the tubular construction, which is, in our perception, far too dangerous; because

we have no substitute if something goes wrong.

 

Our current Philips amplifier; providing 8 Ω and 16 Ω as well as 800 Ω

After, the system is, Deo volente, operating satisfactory, we know the amount of energy is necessitated to operate our substitute display unit.

Thereafter we can provide simpler, and much more space efficient provisions.

Using a stereo amplifier is necessary - as we have to provide similar amounts of deflection energy for the x and y axis deflection-yokes.

One channel has, however, to provide more amplification, as it has to compensate for the signal-loss due to the phase-shifting ladder network.

 

 

(2)   (16 December 2021

Principle schematic as to get painted a first order circular Lissajous on the circular LB 2 CRT

Please notice, that X and Y being interchanged in the drawing above.

The amplifiers provide, at choice, 2 x 800 Ω (supposed sufficient) and also 2 x 8 or 16 Ω.

 

I have drawn one couple of deflection coils vertically and one set horizontally; but it isn't known which one actually have to be fed with the 90 phase-shift signal. As a incorrect connection will cause a counter move of the painted signal video.

Which latter will cause - that when the Nachtfee order signal will rotate opposite as is accomplished with the Nachtfee order pointer;

for example: when the order-pointing being rotated clock wise, the aircraft display will show an anti-clockwise rotation.

YouTube Film

Film 00093:    Viewing the preliminary experimental set-up. The module on the left - in front, is a stereo amplifier; certainly too heavy in power. But is chosen as it should deliver every wanted energy level necessary as to get painted - the first order Lissajous figure - at the fluorescent screen of our LB 2 CRT.     We 'inherited' from Rudolf Staritz's collection a LB 2 CRT inside its deflection Yoke. But, we measured ca. 50 mH for each of the the two (X - Y) sections. Whereas, the deflection Yoke sections measures ca. 1 H (Indicating that it originated from a German wartime aircraft radar set). The Nachtfee PRF is originally 500 Hz, but it is doubtful what amount of deflection energy is necessary as to cope with 50 mH Yoke inductances. When a 500 Hz sine wave signal is demanding a too high driving level, we could consider: 1000 - 2000 or 3000 Hz deflection frequency (the signal signal of 1000Hz will then only appear: every second time per spot rotation, or every fourth time (2000 Hz) or every sixth time (3000 Hz) per full rotation. The oscilloscope is directly measuring across the deflection coils fed via the channel with the 90 phase shifting ladder network. Albeit, that in this experiment we remain using the ladder configuration fit for 90 at 500 Hz only. Our aims, this time, being to watch the signal amplitude across one of the (50 mH) deflection Yokes (coils) (yet unknown is whether it actually concerns the X or Y axis).

 

 

(3)    (29 December 2021)     

Our aim these days being to paint a first order Lissajous circle.

This necessitate that one axis being fed with a sine wave call it constituting the X - axis and the Y - axis has to be fed with the cosine of the the signal which needs a 90 phase-shifting provision.

  The X channel on the left-hand side and the Y-channel on the right-hand side

The painted ellipsoid on the screen is a bit over-exposed

Both using 1 : 10 probes.

It is quite clear that the 90 phase-shifting network isn't operating appropriately.

As to investigate at what signal frequency the ellipsoid axis is being painted horizontally or vertically - I changed the kind of signal source and used instead an analogue signal generator.

 

And at 1000 Hz the ellipsoid axis was parallel onto the Y-Axis

Remaining only adapting accordingly the X - axis amplitude.

 

 

This photo is showing that apparently our 90 phase-shifting network works appropriately at 1000 Hz

 

 

A test brief test was accomplished, whether the generator output impedance had an influence of the performance of our 90 degrees phase-shifting network

It didn't; the only effect noticed was the that over-all signal level changed but not the shape of the painted  ellipsoid.

 

YouTube film

Film 00094:    The experiment today is: investigating at which frequency an ellipsoid being painted exactly parallel onto the X or Y-axis. We normally are using a Philips/Fluke synthesiser at exactly 500 Hz. A circular Lissajous figure can be painted when the signal amplitudes in the X and Y channels are equal and there exists a phase-difference of 90. Pre-condition we need sine-wave signals. As to make life more simple, I took an analogue tone-generator and manually started to go down or up with the generator frequency. It soon proved that going up with the generator frequency the ellipsoid-axis becoming more and more parallel onto the Y-axis of our oscilloscope. And just at 1000 Hz it was exactly parallel and the X-axis amplitude had only to be increased and a sound ellipsoid being displayed.

 

 

(4)

On Thursday 6 January 2022

Hans Goulooze and I have started to get the deflection energy right at the, not yet operational, test set-up.

 

Our first aim today was - to get the supplied voltage across the two deflection coils in line

The oscilloscope down on the trolley shows a more or less correct X - Y deflection pattern across the two deflection X and Y systems (coils). But the sine-wave deflection voltages being actually only ca. 2 volts effectively.

Consequently, what matters are the according deflection currents through the yokes.

But, first it was considered to make our display setup operational. 

 

And, quite surprisingly, it functions rather well, instantly

Apparently, Hans Goulooze has really done a great job.

The tiny blip, about quarter to the our, is derived from the for quite a long time existing Nachtfee substitute interface; in use with the existing aircraft display substitute (since, say, 2013). Its appearance is entirely different from what we encounter at the LB2 display integrated in the Nachtfee console (Please, notice next photograph). However, our aim today is to get some kind of signal-display at our, preliminary, aircraft display reconstruction.

 

Let us, notice how similar LB 2 CRT performs within our Nachtfee Consol, in contrast to the shown performance above.

 

I suppose, that we might have to reconsider the circuit design later, as to provide a more or less similar display presentation as being used within the existing Nachtfee consol (shown here)

But, as to get a similar presentation our circuit has to be re-designed about the deflection cylinder.

 

However,

the tiny signal blip (shown at the second foregoing picture) originated from the since ca. 2013 existing - aircraft display substitute, (rather well operating) interface. Which is being fed from the used Philips/Fluke signal synthesiser and from the FuG 25a transponder.

 

It was also noticed - that the X -Y painted Lissajous is horizontally a bit out of centre (not well visible here).

Therefore, we chose to implement series resonance of the deflection yokes, first. This allowed us to inject, via a resistor, some dc current which variable value and polarity should move the entire Lissajous figure in the X and/or Y planes appropriately.

This provision works sufficiently good.

I suppose - it saturates the magnetic Yoke core(s) more or less.

And, is also allowing us to match favourably sufficient, onto the quite low impedance yoke system.

 

 

This simple circuit is showing our principal schematic; operating series resonance yokes allows us to operate the yoke coils optimally

For our current understanding, it doesn't really matter whether the cosine signal is fed onto the vertical- or the horizontal deflection coils.

In an original German aircraft set - they introduced a DC bias, but in our circumstance we have to deal with the output transformers used with the 800 Ω transformer winding; at one end connected onto ground.

Therefore we have introduced firstly a single series resistor in series with a variable voltage (current) source.

As to get an impression what the actual resonance frequency is - we disconnected the frequency synthesiser (500 Hz) and connected our variable signal source instead, and measured the ac voltages across the terminals a and b; where we get a clear indication of the point of maximal voltage across these noticed terminals.

We knew already, that the voltages across the deflection coils are ca. 2 V ac (sine wave).

Now the deflection currents becoming essential - as at series resonance, the ohmic circuit equivalent is mainly behaving as a real (low ohmic value) resistance (but the coil resistance is also limiting the Q-factor).  

Secondly, it becomes possible to supply in one or both deflection coil sections a DC current in such a way that the painted Lissajous circle is moved within the given graphic CRT scale.

The variable voltage source in series with a resistor is only necessary to minimise the X or Y direction(s)  out-off centre presentation (centre position).

In our case, it was only necessary to shift the X-plane centre (moving its X-plane towards right, a bit).

The only parameter that had to be adjusted was the amplitude of the painted Lissajous. Why?

Because, this type of circular CRT:

 

 

The conical cylinder constructions, are quite well visible

The (circular deflected) electronic beam has to pass just through the space in between the conical inner and outer cylinders.

Logically, when the deflection energy is too high or too low, the electronic beam will not be visible, consequently the electronic beam can't reach the phosphoric screen layer, as it is touching (or even beyond) one of two metal cylinders. Which might even do some harm - as the electronic beam spot can heat up the metal conical cylinder bodies.

In due course, I would like to explain these phenomena by means of an additional YouTube film.

In case of our experiments, the application of the Philips stereo amplifier, allows us, at will, to set for a wide range of deflection amplitudes (currents).

Thus, no screen display, first try to find the correct deflection currents necessary.

 

Down on the left-hand side, we notice the experimental 90 phase-shifting ladder network, as to create the necessary cosine signal path

Adjusted at 500 Hz.

The Lissajous connected across the two deflection yokes painted at the Tektronix oscilloscope, looks perfect, but the pained Lissajous on the CRT screen isn't 100% perfect. (please bear in mind, that the X - Y probes being attached across the deflection coils).  Most likely, now it becomes a matter of fine tuning at resonance of one or both of the deflection yokes (all in series resonance)

 

We actually measured that the real resonance of the two yokes are some 50 Hz below 500 Hz. The problem is, that we have to deal with ca 2.2 F (series) capacitors, and most commercial values are 1 F or 2.2 F. It might be worth to operate 2 x 1F in parallel. Maybe this will minimize the resonance detuning (500 Hz).

Measuring resonance - can be best accomplished by using an analogue electronic voltmeter, and simply watching the points of true resonance (maximal scale pointer deflection), and thereafter comparing what the response at the display will be.

It proved necessary, to detune the phase-shifting ladder-network additionally as to get the over-all (painted Lissajous) performance optimally (maybe also due to some hysteresis).

We have also to bear in mind - that the deflection yokes are being influenced by the properties of the cursive parameters of the metal iron-yoke-cores.

Albeit, the the painted Lissajous at the Tektronix oscilloscope is seemingly perfect (the two probes being across the two yoke sections still) this will not say - that the painted Lissajous on the LB 2 CRT screen is optimally sound, yet.

 

 

To be continued in due course

 

 

By Arthur O. Bauer

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