RAF GEE

GEE

GEE was a Brittish wartime hyperbolic navigation system, used in bomber airplanes of Bomberc Command and airplanes of Coastal Command, like Lancaster, Halifax and Wellington. It was used to maintain the position of the airplane on their way to their targets, often Germany.

An short explainanation of GEE mapping:

By measuring the amount of calibrated pips on the indicator screen, between the  measured beacon pulses from different, fixed GEE transmitters along the country  (so each Gee transmitter gives a high pip on the screen) , and putting these  measurement amounts , called GEE units, in a GEE  map, man could determine the position of the airplane on the map itselves.Each measured GEE  unit has its own hyperbolic curve on that map. In principle, you have to measure 2 Gee units only. The crossing of each curve was the position of the airplane. For more accurency you used more Gee units, so more hyperbolic curves on the map. You have to interpolate the position by these different crossings.

On the internet this system is explaned very often and well.

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The overview of my GEE installation.

Left the GEE receiver with frontend. The receiver is a type R 3645. It is a kind of MF receiver with videoamp. stage. The videostage signal  is fed to the indicator. This receiver picks up the beacon signals which are located on fixed places all in the brittisch countryside.

The frontend is a type 27 b. It converts a tuneable high frequency range of about 65 Mc till 85 Mc into a lower MF frequency of about 6,6 Mc.You could use differnt frontend for different frequency ranges.

In the mid the indicator type 266. On the CRT screen can be seen the beacon-, strobe marker- and calibration pulses.

On the right side the powersupply units, type” voltage control unit no 6″ with its “chokebox no 1″.

These units stabilise a 80 volts 1500 Hz voltage, coming from an alternator.

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Here the original alternator, when I received it from an seller  in the UK, type UKX generator.

Normally it is mechanically driven by one of the airplane engines. It delivers the 24 volts DC and 80 volts 1500Hz. Because of the type it was possible to make it run in connecting the 24 volts parts to a 24 volt battery . All it takes about 30 ampere to let it run! In the left box on the generator (right box is 24 volts part with field connection) you could maintain 80 volts 1500 Hz.

The transformers in the receiver- and indicator powersupplies need a voltage of 80 volts 1500 HZ. The demensions of the transformer get smaller and the weight is less then when you use that frequency. Also other electrical equipment do so. Weight is one of the important fact in an airplane.

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This is my alternator, type UKX. The little switch on the right is switching on a relay in the no 6 unit, which put the 80 volts on the receiver and indicator. The big switch is putting the 24 volt on the alternator.

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Here the powersupply, type Voltage control panel 6, 5U/521. Above the Choke box type1.

These units stabilise the 80 volts from the alternator. Stabilising is needed because of the engine speed is often varying in some circomstances, so the voltage of 80 volts.

In front of it a “ground-flight” switch for switching the whole aircraft installation on the 24 volt from either outside the airplane or airplane batteries themselves. Now used to put the 24 volts on the UKX generator.

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Here the receiver and indicator. On the receiver another frontend unit.

 

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This is the screen of the indicator. You could see here the calibration pips and the negative strobe marker pulses. The measured pulses of the beacon transmitters, called A, B and C pulses are not to be seen. This ofcourse because the GEE systen does not exist any more. The last GEE transmitters went down in the end of the year 1960.

The strobe marker puls could be placed on different places along the X-axes by the red and white knobs  at the under side of the front.. By  Putting down the clearingswitch (you can see then the received beacon pules) you first bring the strobemarker puls just under the measured Gee beacon signals, the clearing switch up, you get the caibration pulses, after that you can measure the distance in calibrating pulses between the beginning of the scales and the strobe markerpulses. These differences are called the Gee units. So the position of the strobe marker at that moment is the position of the beacon signal, e.g. A, B or  C  beaconpuls.

I will once build my self a simulator for it, a schematic is already there etc.The it is possible to give a complete demonstration of the GEE navigation system.

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Another look on the screen with a different time base. Watch the negative strobe marker pulses.

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With the clearingswitch on the indicator, you get the noise  and the GEE beacon signal of the receiver on your screen of the indicator. With the red gainknob on the indicator on maximum, there will be a level of 2 cm on the screen.

 

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Here, the noiselevel is somewhat lower by less gain on the indicator. The red gainknob is regulating the sensitivity of the receiver. When you are receiving the GEE master and slave signals, you can see also the the pulses of about 1 uS on the screen. But because the GEE system does not exist anymore, the pulses are absent.

 

GEEreceiverR3645

Here the front of the GEE receiver, type R 3645. The switch “Z and N ” has an anti jamming function. Often the GEE signals were jammed, in the “Z” position a kind of CW jamming was suppressed then. When no jamming was there, the position of “N” was held. (Normal).

Nice is the lightened scale of the receiver tuning, which indicates also the powersupply is working.

 

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The above side of the GEE 266. Tubes inside are the red VR91.

 

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The side vieuw of the GEE 266.

 

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The other side vieuw of the 266. Right above the EHT tube of the CRT. The compartment on the left under the crystals. On the below centre the MF coils strip of the receiver part.

 

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Above the test set no 210.

This typical test set is used for testing and alighning the GEE installation. It consist of a HF generator, suitable for all the frequencybands of the RF units used in the GEE receiver. All frequency signals unmodulated.

Also a wideband noisegenerator for testing the receiver.

And most import a PRF generator. With this it is possible to generate 15 khz pips on the screen of the GEE indicator. In the test set, there is a generator, which is modulated (switched on and off) by a crystalcontrolled modulator/oscillator. This generator, with it’s frequency tuned on the receiverfrequency of the GEE receiver, is crystalcontrolled by 6 xtals. Frequency A till F. The frequency of the crystals are the same as in the timebase generator of the indicator, in this case the type 266.

By finetuning the PRF (the knob just left of the pilotlamp) on the testset, it is possible to synchronise with the timebase in the GEE indicator. When synchronised, the pips stand still on the screen.

The output of the testset is connected to the GEE receiver input by a coaxialcable.

Also a whip earial can be used, it consist of 3 parts.

The frequency of the generator can be tuned , by a tablechart, by the big black knob at the left on the front.

 

testsetsignaal

Here the 15 khz pips on the the screen of the GEE inicator, type 266. The clearingswitch on the indicator is up, position “receiving GEE signals”. The switch on the test at “modulation on”.

By adjusting the gain on the indicator, the noise level can be taken away, so that only the pips and the strobepulses are left.

The faulty part of the of the timebase at the left is probably a fault in the flyback phase or liniarity of the timebase of the circuit. I left it like that. For demonstrationpurposes it’s not so important.

Posted in General Airforce radio's.

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