Cband gain/pointing after surface adjusted Jan01.

21feb01

The main reflector surface was measured and then adjusted in jan01. After the adjustments, the gain of the system was checked at sband and cband. This page reports the cband results. Other pages concerned with this epoch are:

reflector adjustments jan01
sband gain during and after surface adjusted (jan01)
Pitch, roll, focus correction at multiple frequencies on 3C48, CTA21 (feb01)
cband cals measured jan01 using sky and absorber)
sband focus curve after jan01 reflector adjustment.
cband focus curve after jan01 reflector adjustment.

The observations used the standard 4 strip calibration technique described in the arecibo technical memo 2000-4 : "The Main beam and First Sidelobe parameters for Arecibo's receiver systems". The cband frequencies used were 4500, 4860, 5000, and 5400 Mhz. 8 sources were tracked (although only 2 or 3 were complete tracks) and the gain, SEFD, and pointing errors were computed. The source fluxes were taken from chris salter's most recent flux.cat catalog. The gain computation used the cal values measured in jan01. The 5400 Mhz cal value is probably not very reliable (see the above reference).
The figures show the results of the measurements:

Figure 1 shows the gain versus zenith angle for all the sources and frequencies.
Figure 2 plots the gain versus azimuth angle for all the sources and frequencies.
Figure 3 plots the SEFD (system equivalent flux density) in Jy/Tsys. This tells the source strength needed for a deflection equal to the system temperature.
Figure 4 overplots the SEFD at the four frequencies for the source B0017+154. The 5400 Mhz SEFD does not follow the trend of the other 3.
Figures 5 and 6 show the pointing errors for azimuth and zenith angle.

The measured gain varies from 2 to 6 K/Jy. There should be about a 1 db gain drop off between 15 and 20 degrees za caused by spillover. The misalignment of the optics (pitch, roll, and focus ) will cause some of the other differences (see the Telescope gain with pitch.. reference above).

The SEFD measurements only rely on the source flux. The best SEFD we were getting was 5 to 6 Jy. This occurred for two sources at similar za: B033+133 and B0017+154. This means the fluxes are probably not too far off.

The pointing errors have increased since the last model. the rms error is now:

az 9.4 asecs
za 6.8 asecs
combined: 11.6 asecs

This is similar to what was found for the sband sources (see the above reference).

When the cband cals were measured in jan01 there was a discrepancy in the cal values computed using the absorber or the sky for frequencies greater than 5000 Mhz. This could have been a problem with the cal measurement technique or possibly a loss in the OMT. If it was a loss, then the OMT will reemit at its temperature (70 K). This will throw off the estimation of the input power when the cal is measured relative to the sky (say 18K) and absorber (300K). Figure 3 SEFD plots shows that 5400 Mhz also has a funny SEFD. This lends support to the idea that the receiver is having problems above 5000 Mhz and that it is the system temperature that is increasing.

processing: x101/cb/jan01/doplot.pro

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