Computing the L-narrow Gain
THIS CURVE IS FOR USE FROM JAN 20, 2001 TO AUGUST, 2001
The fit is for 1415 MHz, and is in K/Jy.
The zenith angle (za) and azimuth (az) are in degrees and the (za-15) terms are only used
for za > 15 degrees.
Average Gain [(polA+polB)/2]:
gainavg(az,za,f=1415MHz) = 9.0855699 -0.13198736*za + 0.020340197*(za-15)2
+0.39268538*cos(az) -0.027570212*sin(az) -0.48670176*cos(2*az) -0.064635743*sin(2*az)
+0.076154653*cos(3*az) + 0.090970115*sin(3*az)
8.8121317 -0.12526847*za +0.034930436*(za-15)2 - 0.017510095*(za-15)3
+0.46118491*cos(az) -0.04814893*sin(az) -0.4657348*cos(2*az) -0.060191821*sin(2*az)
How good is the fit for calibrating data:
Errors in the gain measurement come from the measurement technique, the
source fluxes, and the cal values used. The r.m.s. of the fit was 0.56 K/Jy
(.56/9.3= 6%). This probably includes the errors in the source fluxes, but is
also do to the undersampling of the dish. The
data was taken with the lband narrow receiver.
Be aware that if your data lies in an undersampled region of the dish this
curve should be treated with suspicion!! This is particularly true if
your obervations were taken at high zenith angle (za > 17)
A plot of the residuals (really |data-fit|) is below:
Fit for f=1415MHz:
Fit for all frequencies:
Converting the cals to Janskies:
A large uncertainty in the above measurement is the value of the cal in
Kelvins. If the cals are stable over long periods of time, which it
is supposed to be, then we can
use the size of the cal itself as the temperature unit and bypass the uncertainty
in the kelvins/cal. The conversion is: (K/Cal)/(gainK/Jy) =
Jy/Cal. So take the measured calVal and divide it by the gain in K/Jy to
get Jy per cal.
Frequencies other than 1415 Mhz:
Although the `new' cal values were applied to the data, it still appears that
there is an offset between the predicted and observed values, particularly at
1300MHz and 1500MHz. This can be seen in the plot below, where data for all
four boards (1300MHz, 1375MHz, 1415MHz, and 1500MHz) is shown and an offest
is visible for the same source at a given zenith angle.
This offset, though, appears to be in the 5\% error range.
Hopefully new cals values will be obtained soon which will eliminate these offsets.
The old (pre June 26, 2001) fit (the precursor to this one),
which you SHOULD NOT USE can be obtained
Monday, 03-Dec-2001 14:50:04 AST