cross scans with Mathew's 430 MHz test feed
The system performance of Matthew's 430 Mhz dipole
feed was measured on 06nov05 doing cross scans on J1330+305 (3C286) and
J1419+064. These measurements were done with the feed in the same
position as the 22sep04
measurements. For these measurements the cal diodes were installed
so we got Tsys as well and gain/sefd. Cross scans were done on the
430 dipole and on the 430 linefeed. The setup was:
The plots show the
system performance (.ps) (.pdf):
1 degree strips (4 crosses with on the 430 dipole and then 4 on the
linefeed) were done followed by 1.5 degree strips (18 crosses on the 430
dipole and 3 crosses with the linefeed). We switched to the longer strips
so the first sidelobe (30 arcminutes away) was included in the strip.
The dipole feed adds the polarizations together. The lr1 polarization of
the linefeed was used for the 430 linefeed measurements.
The signal was centered at 430 Mhz and was passed through a 1 Mhz butterworth
IF filter. Each strip took 60 seconds. The signal was detected with a .2
sec time constant and then sampled at 10 hz.
At the beginning of a set of crosses, the cal was fired for two seconds
to measure Tsys. The cal values used were: dipole cal:42.1, linefeed cal:
2d gaussians were fit to each cross. The fit included a rotation angle
for the ellipse as well as a linear term in za (for changes in tsys). The
first sidelobes were excluded from the fit.
The flux used for the two sources was: 3C286=24.3 Jy, J1419+064=26.5 Jy.
Fig 1 shows the individual strips:
Top: dipole strips on 3C286. Black are azimuth strips, red are za
Center: dipole strips on J1419+064. Green are azimuth strips, blue are
Bottom: line feed strips.
Fig 2: The average of the dipole strips after removing the system
temperature. Each strip was rotated by the measured pointing error before
averaging. The az strip is black and the za strip is red. The top plot
is linear (in degK). The bottom plot is db below the peak. The za
beam width is a little larger than the az beam width. The az sidelobes
are 10 db and 28 Amin from the peak.
Fig 3 has the Gain and Tsys. 3C286 is in black while J1419+064 is in red.
The gain for the dipole does not fall off in za as the linefeed. The dipole
Tsys measurements of J1419+064 seem to jump: 4 low, 4 high. There was only
1 cal measurement for each of these groups. It could have been the cal
measurement (but the sefd also shows this difference and it does not use
Fig 4 : sefd and beam widths. The top two plots are the sefd (source flux
needed to equal the system temperature). The two sources are color coded.
The bottom two plots are the beam widths from the fits. * is the azimuth
beam width and + is the za beam width. The dipole has a beam width of 18
amin and the linefeed has a beam width a little less than 10 amin.
Fig 5: The pointing error measured from the fits. The values are in great
circle arcminutes. The top plot is the dipole and the bottom plot is the
linefeed. The ch model was used for pointing with great circle offsets
of: az .5, za -1.6 degrees. These measurements say that the
offsets should have been: az:.4833 deg, za: -1.5483 deg.
|az pnt err (avg)
zapnt err (avg)
|az pnt offset used:
ch pnt offset used
| 0.5 deg
|az pnt offset measured
za pnt offset measured