Editing Infrared homing (section)

====Hamburg system====
The ''Hamburg'' system developed during the war is the simplest system, and easiest to understand. Its chopper was painted black on one half with the other half left transparent.{{sfn|Kutzscher|1957|p=212}}

For this description we consider the disk spinning clockwise as seen from the sensor; we will call the point in the rotation when the line between the dark and light halves is horizontal and the transparent side is on the top to be the 12 o'clock position. A photocell is positioned behind the disk at the 12 o'clock position.{{sfn|Kutzscher|1957|p=212}}

A target is located just above the missile. The sensor begins to see the target when the disk is at 9 o'clock, as the transparent portion of the chopper is aligned vertically at the target at 12 o'clock becomes visible. The sensor continues to see the target until the chopper reaches 3 o'clock.{{sfn|Kutzscher|1957|p=212}}

A [[signal generator]] produces an AC waveform that had the same frequency as the rotational rate of the disk. It is timed so the waveform reaches its maximum possible positive voltage point at the 12 o'clock position. Thus, during the period the target is visible to the sensor, the AC waveform is in the positive voltage period, varying from zero to its maximum and back to zero.{{sfn|Kutzscher|1957|p=212}}

When the target disappears, the sensor triggers a switch that inverts the output of the AC signal. For instance, when the disk reaches the 3 o'clock position and the target disappears, the switch is triggered. This is the same instant that the original AC waveform begins the negative voltage portion of its waveform, so the switch inverts this back to positive. When the disk reaches the 9 o'clock position the cell switches again, no longer inverting the signal, which is now entering its positive phase again. The resulting output from this cell is a series of half-sine waves, always positive. This signal is then smoothed out to produce a DC output, which is sent to the control system and commands the missile to turn up.{{sfn|Kutzscher|1957|p=212}}

A second cell placed at the 3 o'clock position completes the system. In this case, the switching takes place not at the 9 and 3 o'clock positions, but 12 and 6 o'clock. Considering the same target, in this case, the waveform has just reached its maximum positive point at 12 o'clock when it is switched negative. Following this process around the rotation causes a series of chopped-off positive and negative sine waves. When this is passed through the same smoothing system, the output is zero. This means the missile does not have to correct left or right. If the target were to move to the right, for instance, the signal would be increasingly positive from the smoother, indicating increasing corrections to the right. In practice a second photocell is not required, instead, both signals can be extracted from a single photocell with the use of electrical delays or a second reference signal 90 degrees out of phase with the first.{{sfn|Kutzscher|1957|p=212}}

This system produces a signal that is sensitive to the angle around the clock face, the ''bearing'', but not the angle between the target and the missile centerline, the ''angle off'' (or ''angle error''). This was not required for anti-ship missiles where the target is moving very slowly relative to the missile and the missile quickly aligns itself to the target. It was not appropriate for air-to-air use where the velocities were greater and smoother control motion was desired. In this case, the system was changed only slightly so the modulating disk was patterned in a [[cardioid]] which blanked out the signal for more or less time depending on how far from the centerline it was. Other systems used a second scanning disk with radial slits to provide the same result but from a second output circuit.{{sfn|Kutzscher|1957|p=214}}