Power Measurement Calibration Factor
When measuring power, the Homer uses an internal power calibration factor C, stored in its memory. The value of C is set to unity in the factory at the time of the Homer calibration.
The user can modify C to be anywhere within the range 0.1 to 10 (-10 dB to +10 dB).
However, rather than entering C directly, it is more natural to enter a number which should multiply the currently displayed power to obtain the desired power reading. This number is called the calibration factor multiplier (M). Mathematically, M multiplies the current power calibration factor to obtain its new value:
C_new = C_current * M
The bounds on allowable M depend on the current value of C, such that their product always remains within the permitted range of 0.1 to 10:
M_min = 0.1 / C_current
M_max = 10 / C_current
The user can change the current calibration factor or restore it to unity.
To perform the described actions, click the Homer|More|Pow Cal Factor menu item. Following this, the window titled Power Measurement Calibration Factor appears (Fig. 56).
Fig. 56. Power Measurement Calibration Factor window.
The controls and displays are organized in two groups, CAL Factor Multiplier and Lin CAL Factor.
CAL Factor Multiplier Group
The group displays the current calibration factor multiplier M and enables the user to modify it. The radio buttons Lin or dB determine whether M is displayed and will be entered in linear format or in decibels. The conversion is via the formula M_dB = 10*log(M_lin). After opening the dialog window, the starting value of M is always 1 (0 dB).
Clicking the button opens a dialog for editing the multiplier M. The permissible bounds on the new value are automatically computed and the user is not allowed to exceed them.
The changes made are reflected in the Lin CAL Factor group, but they will not be accepted until the button is clicked (see the next section). The button discards the modifications made, leaves the current calibration factor unchanged and closes the dialog window.
Lin CAL Factor Group
Current shows the currently valid power calibration factor C. This value cannot be modified directly; instead, it is updated by adjusting M in the CAL Factor Multiplier group.
New previews the value of C which would result from applying the multiplier M to the current value.
The button activates the procedure of writing the new calibration factor to the Homer memory and closes the dialog window.
The button returns the power calibration factor to its original factory setting C = 1 and closes the window.
To change the power calibration factor:
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Determine the calibration factor multiplier M.
Example 1: The Homer reads 985 W and you wish the reading to be 1000 W. The required multiplier in linear format is M = 1000/985 = 1.0152.
Example 2: The Homer reads 59.93 dBm and you wish the reading to be 60 dBm. The required multiplier in decibel format is M = 60 - 59.93 = 0.07 dB.
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Click the Homer|More|Pow Cal Factor menu item.
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Click the Lin radio button (in the case of Example 1) or dB radio button (in the case of Example 2).
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Click the button. A dialog for entering a value opens. Type in the required M (1.052 for Example 1 or 0.07 for Example 2); then click .
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If you are satisfied, click the button, otherwise click .
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Verify the modified calibration factor. You can do so by checking the value in parentheses of the Homer|More|Pow Cal Factor menu item, or by reopening the dialog via the Homer|More|Pow Cal Factor menu item.
To restore power calibration factor to unity:
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Click Homer|More|Pow Cal Factor.
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Click the button.