SC5305A Operating & Programming Manual
Rev 2.1.0
27
Table 11. Localized parameters for spline interpolation.
Frequency (MHz);
850
900
950
1050
1100
1150
Gain;
32.681
32.673
32.652
32.482
32.419
32.418
1000
32.532
To find the change in gain with respect to change in temperature involves a couple of steps; first
determine the array values of
, where
is the frequency point at which a measurement was
made, and then as a second step, use interpolation to determine the
at some frequency
.
Again, natural cubic spline interpolation is recommended in the second step. Let us outline a method to
determine
at frequency
; there are a total of eight frequency points for this calibration.
The calibration values retrieved from the EEPROM are second order polynomial coefficients fitted to
measured data. Writing the general form of the gain function using coefficients, we have:
Equation 4
Here
is the
order coefficient measured some frequency
. The gain deviation at temperature
from the gain measured at the calibration temperature
can be written as
Equation 5
Using Equation 5 and the temperature coefficients of Table 6, we obtain the following:
Table 12. Calculated gain changes at the measured frequency points.
Frequency (MHz)
50.0
250
500
1000
1500
2500
2800
3800
dB
-0.340
-0.343
-0.351
-0.348
-0.354
-0.351
-0.355
-0.357
After determining the set of gain deviations at some temperature
, we apply spline interpolation to the
set of
values to obtain
, change in gain with respect to both temperature and
frequency. Using Table 12 and the convention developed here, the spline parameters are
,
,
, and
.
IF Response Correction
The gain correction procedure outlined above only applies to a signal that is centered in the 70 MHz IF
band. The device’s Fine-Tune mode (1 Hz) is able to place any RF signal at the center of the IF, so for
narrow bandwidth signals (typically less than a MHz), applying the center IF gain correction and
assuming no deviation from linear phase is sufficient. However, for a large bandwidth signal that spans
several MHz, it is important to apply gain and phase correction to the offset frequencies; those that are
offset from the center IF. Although SignalCore performs calibration of the amplitude and phase over the
bandwidth of the IF filters (available on the device calibration EEPROM), it is recommended that the
user perform in-situ system equalization for digital broadband applications for improved performance.