Radio Altimeters

Lufthansa had Collins Radio Altimeters installed on their B707 fleet (both A and B version). These are the most commons found on early jets built in the US. I found these in U/S condition on ebay and thus they were the perfect candidate for the simulator conversion. This Radio Altimeter includes a minima selector that allows you to select the desired DH for CAT II approaches. It is in important feature I did no want to miss and was able to rebuild the gauge with a hollow shaft potentiometer. Usually the gauge has a minima light that comes on when the aircraft descents below the DH (Decision Height). This light was removed pretty early in the LH 707 ops as the DH light on the Sperry HZ-6 artificial horizon was used.

This is a photo of D-ABUF just before retirement. As you can see the minima light was removed (displayed on HZ6 Horizon)
As I do not have the original plugs I am using DSUB 25 pin plugs.
Wiring the gauge. Note the stepper motor that can be run with 0,001° accuracy.
360° potentiometers usually have a range of 340° and thus a 20° “dead-zone”. Here I am adjusting the dead zone to fit between the 25 and -20 to be able to use the full 340° range on the scale.
Redesigning the dial. To be replaced at a later date when I have the exact font for “HEIGHT”