Computing the L-narrow Gain

g(az,za) fit:

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