Due to the arrangement of the receiver antennas, the sensitive area had a number of side lobes that allowed reception at multiple vertical angles.
Typically the operator would use the upper set of antennas at 215 ft (66 m), which had the clearest view of the horizon.
Due to the half-wave interference from the ground, the main lobe from this antenna was directed at about 2.5 degrees above the horizontal, with its sensitive region extending from about 1 to 3 degrees.
At the ground the gain was zero, which allowed aircraft to escape detection by flying at low altitudes.
The second lobe extended from about 6 to 12 degrees, and so on.
This left a distinct gap in the reception pattern centred at about 5.2 degrees.

This reception pattern provided CH with a relatively accurate way to estimate the altitude of the target.
To do this, the motorized switch in the receiver hut was used to disconnect the four receiver masts and instead select the two vertically displaced antennas on one mast.
When connected to the radiogoniometer, the output on the display was now effected by the relative signal strength of the two lobes, rather than the relative strengths in X and Y in the horizontal plane.
The operator swung the radiogoniometer looking for the peak or minimum reception, as before, and noted the angle.

The number reported by the operator was the line-of-sight range to the target, or slant range, which included components of both the horizontal distance and altitude.
To convert this to the real range on the ground, the plotter used basic trigonometry on a right angle triangle; the slant range was the hypotenuse and the open angle was the measurement from the radiogoniometer.
The base and opposite sides could then be calculated, revealing the distance and altitude.
An important correction was the curvature of the Earth, which became significant at the ranges CH worked at.
Once calculated, this allowed the range to be properly plotted, revealing the grid square for the target, which was then reported up the chain.

When the target was first detected at long range, the signal typically did not have enough of a return in the second lobe to perform height finding.
This only became possible as the aircraft approached the station.
Eventually this problem would recur as the target centred itself in the second lobe, and so forth.
Additionally, it was not possible to determine the difference between a signal being compared between the first and second or second and third lobe, which caused some ambiguity at short ranges.
However, as the altitude was likely determined long before this, this tended not to be a problem in practice.

Unfortunately this pattern left a set of distinct angles where reception in both lobes was very low.
To address this, a second set of receiver antennas were installed at 45 feet (14 m).
 When the two lower sets of antennas were used, the pattern was shifted upward, providing strong reception in the "gaps", at the cost of diminished long-range reception due to the higher angles.
Due to the arrangement of the receiver antennas, the sensitive area had a number of side lobes that allowed reception at multiple vertical angles. Typically the operator would use the upper set of antennas at 215 ft (66 m), which had the clearest view of the horizon. Due to the half-wave interference from the ground, the main lobe from this antenna was directed at about 2.5 degrees above the horizontal, with its sensitive region extending from about 1 to 3 degrees. At the ground the gain was zero, which allowed aircraft to escape detection by flying at low altitudes. The second lobe extended from about 6 to 12 degrees, and so on. This left a distinct gap in the reception pattern centred at about 5.2 degrees.
This reception pattern provided CH with a relatively accurate way to estimate the altitude of the target. To do this, the motorized switch in the receiver hut was used to disconnect the four receiver masts and instead select the two vertically displaced antennas on one mast. When connected to the radiogoniometer, the output on the display was now effected by the relative signal strength of the two lobes, rather than the relative strengths in X and Y in the horizontal plane. The operator swung the radiogoniometer looking for the peak or minimum reception, as before, and noted the angle.
The number reported by the operator was the line-of-sight range to the target, or slant range, which included components of both the horizontal distance and altitude. To convert this to the real range on the ground, the plotter used basic trigonometry on a right angle triangle; the slant range was the hypotenuse and the open angle was the measurement from the radiogoniometer. The base and opposite sides could then be calculated, revealing the distance and altitude. An important correction was the curvature of the Earth, which became significant at the ranges CH worked at. Once calculated, this allowed the range to be properly plotted, revealing the grid square for the target, which was then reported up the chain.
When the target was first detected at long range, the signal typically did not have enough of a return in the second lobe to perform height finding. This only became possible as the aircraft approached the station. Eventually this problem would recur as the target centred itself in the second lobe, and so forth. Additionally, it was not possible to determine the difference between a signal being compared between the first and second or second and third lobe, which caused some ambiguity at short ranges. However, as the altitude was likely determined long before this, this tended not to be a problem in practice.
Unfortunately this pattern left a set of distinct angles where reception in both lobes was very low. To address this, a second set of receiver antennas were installed at 45 feet (14 m).  When the two lower sets of antennas were used, the pattern was shifted upward, providing strong reception in the "gaps", at the cost of diminished long-range reception due to the higher angles.
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