Computing the L-narrow Gain
The fit is for 1405 MHz, and is in K/Jy.
The zenith angle (za) and azimuth (az) are in degrees and the (za-14) terms are only used
for za > 14 degrees.
Average Gain [(polA+polB)/2]:
gainavg(az,za) = 8.78131
-.11062 *za + ( .00183)*(za-14)^2 +(-.00310)(za-14)^3
+ .37864*cos(1az) + ( .16833)*sin(1az)
-.10007*cos(2az) + ( .02403)*sin(2az)
-.26800 *cos(3az)- (.14245)*sin(3az)
The fits for Polarization A (pola) and Polarization B (in K/Jy) are:
Gain_PolA(az,za)= 8.92204 -(0.11083)*za +( 0.00214)*(za-14)^2 +(-0.00342)(za-14)^3
+ .41611*cos(1az) + ( 0.18207)*sin(1az)
-0.10120*cos(2az) + ( 0.02740)*sin(2az)
-0.30386*cos(3az) + (-0.14610)*sin(3az)
Gain_PolB(az,za)= 8.64057 -(0.11041)*za +( 0.00152)*(za-14)^2 +(-0.00278)(za-14)^3
+0.34117*cos(1az) + ( 0.15459)*sin(1az)
-0.09894*cos(2az) + ( 0.02066)*sin(2az)
-0.23214*cos(3az) + (-0.13879)*sin(3az)
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 0.25 K/Jy
(.25/9= 3%). This probably includes the errors in the source fluxes. The
data was taken with the lband narrow and lband wide receivers which have
different cals. Two sources were measured using both systems. The
ratio of the gains were gainlbw/gainlbn = 1.05. Assuming the gains are
the same (even though the horn illumination is a bit different) then the
cals differed by 5%. This is a systematic error. The lbw gain values were
scaled to the lbn scale (decreased by 5% since there were many more lbn
measurement than lbw). On the other hand, the lbw cal is 5 times larger
than the lbn cal (10,1.9) so it is probably a better cal to use.
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. Most of this data was taken with the lbn cal but
a fraction of it was taken with the lbw cal and then scaled to the gains
we got with lbn cal. You should probably only use these equations with
the lbn cal.
Frequencies other than 1400 Mhz:
The large variation in gains for the 1290,1370, and 1460 Mhz makes it doubtful
that the lbn cal is a constant over this frequency range so the gain in
K/Jy is incorrect. It is still valid to compute the cal in Jy using the
gain(az,za) equations for each of these frequencies and the 1420Mhz cal
value (since that is what was used to compute the K/Jy gains). These gains
(1290,1370,1460) will be provided separately.
Note that for the L-Narrow, the OLD cal values of 1.85 and 1.91
were used to generate these curves!
For more information on the calibration data, you can go to Phil Perrilat's
web page, which is located here.
Last Updated 09 May, 2001