lband receiver on the carriage house (seti@home)

oct,2002

Intro.

LINKS:
Intro.
01jul02: Crosses on J0840+132 to check pointing and gain.

Intro:

A 16 foot linefeed on the carriage house (lbch) is dedicated to the serendip (seti@home) program. They observe full time with this feed while other people use the dome or carriage house. The pointing models for the dome are built with the carriage house at stow position (8.8 degrees za) so most of the time the lbch feed is sitting at 8.8 degrees. The feed will then be able to see +/- 8.8 degrees from arecibo's declination (18 degrees). When the dome moves at sidereal rate to track a source, the lbch will be moving at twice sidereal rate. As the dome moves to lower zenith angle, the azimuth motion increases to keep a constant rate on the sky. Since lbch stays fixed at 8.8 degrees za its speed on the sky will increase by sin(8.8)/sin(zadome).

01jul02: Crosses on J0840+132 to check pointing and gain.

Azimuth/zenith angle crosses were done on the source J0840+132 on 01jul02 to check the pointing. The source was tracked from za=6 degrees until it set. A 5 Mhz bandwidth was detected with a 20 millisecond time constant and sampled at 100 hz. Each leg of the cross was 30 arcminutes (great circle) long. 23 crosses were taken and then 2-D gaussians were fit to each cross giving Tsys, srcStrength, pointing errors in azimuth and zenith angle, the beam widths for the major and minor axis of the beam ellipse, and the rotation angle to go from azimuth to the major axis of the ellipse. The plots show the results of the data taking.

Fig 1 top. This is the raw data for a single cross. The units are A/D counts. The blue lines are the fits to each strip.
Fig 1 bottom. The dome was being moved by maintenance while we were taking this data. The bottom plot shows the dome position as a function of the carriage house position. This motion could change the pointing error.
Fig 2. The pointing error is plotted versus za (top) and versus azimuth (bottom). The black is the great circle error in the azimuth direction and the red is the error in the zenith angle direction. To figure out the sign convention notice that the azimuth error is always positive. Looking at fig 1 we see that the source is coming after the expected position (it is > 0). If we wanted to point the telescope at the source (with no error) we would add zaComp+zaErr, azComp + azErr/sin(za) to the original encoder values that were used to point at the source. The increase in za error from za=10 to za=15 is probably the dome moving from 19 deg down to 10 degrees (about a 1 arc min variation).
Fig 3 has the beam width in arcminutes for the lbch. The average is 5.1 arcminutes.
Fig 4 plots the variation in Tsys versus za (top) and the SEFD bottom for the system. Since SEFD*gain=Tsys a Tsys of 70 K would give a gain of 2 K/Jy.

To figure out where the seti@home is currently pointing do the following:

Take the recorded az1,za1, ast time from the serial link.
Compute the model offsets mazoff,mzaoff at az1,za1. The model values are great circle so you need to divide the azimuth offset by sin(za) to go from great circle to azimuth encoder.
Compute the values prior to the model: az2=az1-maz1, za2=za1-mza1
Take the great circle errors measured in fig2 above: merraz,merrza and compute the encoder offsets: erraz=merraz/sin(za), errza=merrza.
compute the theoretical az,za that will be used to go back to ra, dec: az3=az2-erraz, za3=za2-errza.
Take az3,za3, the time, and the ao lat,long to go back to ra,dec.

processing: x101/020701/doit.pro

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