Alfa cal values measured in lab (apr04)
The alfa high cal was measured in the lab in apr04.
The noise figure analyzer was used stepping the frequency by 10 Mhz for
each measurement. A warm omt was used to couple the NFA signal into the
receivers omt (the horn was not installed). The measured data was fit with
a 3rd order polynomial over the range 1230 to 1520 Mhz. The data
is plotted in black with the fits in red. Dashed green lines mark the boundary
of the alfa band (1220 to 1520). The plots show:
There is a high frequency structure in some of the measured
cals with a period of about 50 Mhz. This would be 3 meters in air. The
Tsys/Tcal ratio also has frequency structure at the 25Mhz level. Both of
these measurements were made with "temporary setups". We should try remeasuring
the cal values using sky and absorber and the alfa if/lo chassis. For now
the cal values will be those of the 3rd order fit
cal value versus frequency:
Figure 1: Pol A measured cal values (black) and 3rd order fit (red) for
the 7 pixels.
Figure 2: Pol B measured cal values (black) and 3rd order fit (red) for
the 7 pixels.
Figure 3: PolA residuals (data - fit) .
Figure 4: PolB residual s (data - fit).
Figure 1: Tsys/Tcal versus frequency. The top plot is polA the bottom plot
is polB. Each pixel is plotted in a different color. The data was taken
while tracking blank sky using the old if/lo system (the lbw cables were
plugged into each pixel one at a time since the alfa rf box had not yet
been installed). There was no rf bandpass filter installed (although the
IF was 750 Mhz).