25 November 2017
Page initiated 6 July 2017
Status: 8 July 2017
Our aims are, for this occasion, to explain Nachtfee in its operational context.
Therefore focussing more on the implications of the "domains of time" than on technical aspects.
This basic drawing has been, very kindly, made by Wim Witt (PA 0 WDW), whilst the additional matters are mine
It took me at least two years before I started to (really) grasp the implications of a flying object controlled by a ground station - where the entire system is relying upon signal phase manipulations.
The main purpose of our Seminar is to show: - that the concerned system data is dependant upon distance, and distance considered (viewed) from a certain position is related to the time signals need to 'travel' from one point to another.
Without bringing the proof, it is quite comprehensible, that the actual "signal-phase-shift" generated by the controlling Nachtfee station on the left-hand side and the position ➀ takes less transit-time than towards, for example, aircraft position ➇; which might be at, say, 200 km and beyond range.
Technically: we don't deal here with modulated signals as usual, but with only "a single phase-shift-value"; each one constituting a particular order or command; thereafter no one can, ever, measure that something once has been changed. The crucial bottleneck was the reliability (accuracy) of both clock- or time-base references (quartz oscillators, one in the Nachtfee console, and one in the aircraft). Nevertheless, we have quite recently proved that (only) with nowadays affordable Rubidium standards that such system could have operated reliably.
But don't worry - these latter considerations aren't dealt with, during our Seminar.
However, on the ground they would like to know, among some other data, what the actual position of the controlled aircraft is, and we know distance implies time; as wireless signals travel with the speed of light*. That is why we have to operate in the ‘domains of time’. Not using moving-coil meters - but all being accomplished by means of watching crt screens, and operating some controls; the (first) main ones shown in our animation drawing on the right-hand side.
* approx. 300.000 km/s. Radar signals operated, particularly in those days, with signal pulses, which recurrence frequency was known as PRF. Freya and according IFF (Identification between Friend or Foe) recognition, signals operated in Germany at a PRF rate of 500 Hz. The wave-length λ of such signal is 600 km; in radar terms 300 km, as signal has to travel the range twice. Therefore the normal Nachtfee operational range was limited to 300 km. Each painted crt circle representing 300 km range (each spot rotation lasting 2 ms).
Don't be afraid for mathematics, we only consider, for this occasion, the interactions between distance and (phase) time.
To be continued in due course
By Arthur O. Bauer