This is yet an experimental page, as it is the first time I have uploaded a films onto YouTube

Initiated on: 26 September 2012

Status: 27 September 2012

•     Nachtfee testfilm 1    We are looking at the returning signals from the FuG25a transponder. What do we see? The main signal (often) due North is the returning time-base signal phase, which is injected at Rö8, thus directly in the TX keying circuit. Its signal is thus not interrupted by means of Morse keying. The signal blips at, say, 'two minutes before the hour' is the returning Nachtfee 'order' or command pulse; which have passed through the FuG25a transponder, like is doing the simulated Freya-EGON signal. However its PRF is not equal to the one of Nachtfee, and consequently, is going faster or slower (please see: Nachtfee testfilm 2) We are monitoring the range of signals returning into the Nachtfee via the feedback input (Impulsamplitude channel). Please notice also, that when the 'Phase' control is being operated, that the returning simulated aircraft time base reference is changing its vector whereas the returning (via the transponder) Nachtfee 'order' blip is not changing its vector. The returning received signals are being keyed by means of the recognition keys 'nal 1 or nal 2'.  

•     Nachtfee testfilm 2    We are monitoring the actual dual HF signal message towards the simulated aircraft display (directly measured at 124 MHz). I have experimentally changed the EGON PRF as to show what its implication is. The slowest pulse movements is the hypothetical EGON PRF differing only 2 Hz. Thus, 506.xx versus 508 or 504 Hz. The quasi stationary pulses represent the Nachtfee 'order' signal, because our oscilloscope is being triggered upon. The second moving signal originates from the simulated Freya-EGON system, which originally was meant for measuring distance; acting as a 'secondary radar' signal. Please notice also the British wartime observation report of 1944 (Bladwijzer179)

•     Nachtfee testfilm 3    We are watching the Nachtfee signal on the simulated Nachtfee/FuG136 aircraft display. We are actually looking at the Nachtfee 'order' signal with the simulated EGON measuring signal having a different PRF (500 Hz)

•     Nachtfee testfilm 4    Watching the Nachtfee 'order' signal blip with the differently rotating EGON signal. Please notice the constant drifting of the Nachtfee 'order' signal versus the simulated aircraft time base. Drift originating from the nachtfee console time base only!

•     Nachtfee testfilm 5    Viewing the Nachtfee 'order'signal blip, though, also retransmitting both the EGON as well as the original Nachtfee 'order' signal. Retransmission is causing a shadow signal having a different vector (blip). Whether this is a conceptional error or a fault in our FuG25a apparatus I don't know yet.

•     Nachtfee testfilm 6    Please notice  that the shadow pulse is following its main pointer vector, but is still victim to the non existing synchronism between the Nachtfee ground console and the simulated aircraft display system.   

•     Nachtfee testfilm 7    Please notice the considerable difference between both the simulated aircraft time base (derived from the PM5193 synthesiser) and the Nachtfee data signal (measured using Q8 at 506.xx Hz)

•     Nachtfee testfilm 8    Viewing the data available at the FuG25a test pin 9. We are looking at both Nachtfee and EGON signal.

•     Nachtfee testfilm 9    Viewing the neon indicator of BG25a, the control box of the FuG25a IFF system. The flashes indicate that HF is provided at the output of the TX stage. We are, however, absorbing its energy into a dummy-load. The flashes is switched on and of in a: dash - space - dash - space - dash sequence.   

•     Nachtfee testfilm 10    Viewing the received signals of the FuG25a RX, the flashing signals originate from the simulated Freya-EGON system as well as from nachtfee. Please notice the quasi running away of both time bases

•     Nachtfee testfilm 11    Viewing the Nachtfee LB2 CRT presentation, where the main blip is representing the returning simulated aircraft time base, versus the 'Phase' control on the front panel. Adjustment would not have been possible when it would have concerned the Nachtfee 'order'data, as this is in coherence and is not controle by Phase settings at all.   

•     Nachtfee testfilm 12    Viewing the two Nachtfee CRTs where Phase control is being adjusted. On the left-hand side the exact adjustment and on the right the corresponding phase vector returning from the simulated aircraft display.   

•     Nachtfee testfilm 13    Phase shifting is becoming less, still to be controlled by the Nachtfee 'Phase' control setting.

•     Nachtfee testfilm 14    We have reached 'quasi synchronism' between both the Nachtfee and the simulated aircraft time base.

•     Nachtfee testfilm 15    Viewing the simulated aircraft system, where the Nachtfee time base frequency has more or less stabilised 506.032 Hz (although, still not 100 stable) The pulse blip at say 20 past the hour is the actual nachtfee data pulse. The brighter blip at 15 minutes past is the shadow simulated aircraft time base signal, due to the fact that the TX signals return into the FuG25a RX and is then retransmitted again.

To be continued in due course

By: Arthur O. Bauer

Please consider also the new     testfilm series 2 and testfilm series 3