cross scans after yagi moved closer to lineFd
01aug06 system performance (.ps) (.pdf):
the system performance of 01aug06 and may06 (.ps) (.pdf)
The 430 Mhz yagi antenna was moved closer to the line
feed around 25jul06. The feed offsets were:
Yagi offset from center of line feed
||.4833 deg / 3.7 ft
||-1.5483 deg /11.8 ft
||1.62 deg / 12.3 ft
||.8093 deg / 6.1 ft
||-.9157 deg / 7.0 ft
||1.22 deg / 9.3 ft
The system was calibrated on 01aug06 using 3C286
(24.3Jy at 430Mhz). This was the same source that was used on 29may06.
12 crosses were done with the yagi and 3 crosses with the linefeed.
The new low loss cable between the yagi and the amplifier had not yet been
installed. The setup was:
1.5 degree strips (12 crosses on the 430 yagi and 3 crosses with the linefeed)
The yagi feed adds the polarization's together. The lrr1 polarization of
the linefeed was used for the 430 linefeed measurements.
The signal was centered at 430 Mhz and was passed through a 2 Mhz butterworth
IF filter. Each strip took 90 seconds. The signal was detected with a .02
sec time constant and then sampled at 100 hz.
At the beginning of a set of crosses, the cal was fired for two seconds
to measure Tsys. The cal values used were: yagi cal:124.9, 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 source was 24.3Jy
The fit was iterated to get rid of some of the interference that occurs
with a 1 minute spacing.
The plots show the
01aug06 system performance (.ps) (.pdf):
The 01aug06 data (top)
Fig 1 shows the individual strips:
Top: yagi strips on 3C286. Black are azimuth strips, red are za strips.
The data has been smoothed by 5 samples.
Bottom: line feed strips.
Fig 2: The average of the yagi 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 9 db and 30
Amin from the peak.
Fig 3 has the Gain and Tsys. The gain is about 1.5 K/Jy. Tsys in
490 K at za of 11 and goes up to 500K at a za of 18.
Fig 4 : sefd and beam widths. The top two plots are the sefd (source flux
needed to equal the system temperature). The bottom two plots are the beam
widths from the fits. * is the azimuth beam width and + is the za beam
width. The yagi has a beam width is about 17 Amin. 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. New offsets were measured manually before taking this
data. The pointing errors measured are relative to these new offsets. The
top plot is the yagi and the bottom plot is the linefeed. The ch model
was used for pointing with great circle offsets of: az: .75 deg, za: -.93
deg. The average yagi pointing errors are 3.56 Amin az and -.92 amin za.
The pointing errors should be added to the offsets . These pointing
errors say the offsets should have been: az: .809, za: -.9453 deg.
The plots compare
the system performance of May06 and Aug06 (.ps) (.pdf)
. The black * are 01aug06 and the red * are 29may06.
Comparing the 29may06
and 01aug06 data (top)
Page 1 top: Gain (K/Jy) for yagi and line feed). The yagi gain on 29may06
was about 6% higher than 01aug06. The carriage house (ch) gains were the
same on the 2 days.
Page1 Bottom: Tsys (K) for the yagi and the line feed. The yagi Tsys on
01aug06 was a little higher than tsys on 29may06.
Page 2 Top: Sefd for yagi and ch. The yagi sefd increased by about 10 %
from may06 to aug06. This measurement does not use the cal values. That
means that the offsets seen in the gain and tsys are probably real (and
not problems with the cal changing). The ch sefd remained pretty
stable on the two days.
Page 2 Bottom: The beam widths for the yagi and ch. These remained the
same for the two dates.
Page 3 pointing errors: The + are the az errors while the * are the za
errors. These errors should not be the same since the 01aug06 position
was a rough position to start with.
The comparison between the linefeed and yagi for
|1st side lobe (db)
||az :-9.5 db
za: -12 db
|az pnt err (avg)
zapnt err (avg)
|az pnt offset used:
ch pnt offset used
| 0.75 deg
|az pnt offset measured
za pnt offset measured
The yagi gain decreased and tsys increased between 29may06 and 01aug06
(before/after the move). This is probably real and not a problem with the
cals since the sefd also increased by about 10%. I wonder if the
antenna is at the optimum position?