Operator`s manual

Haystack Observatory - - Small Radio Telescope
Measure Antenna Beamwidth using the Sun as a Signal Source
Introduction:
The beamwidth of a radio telescope is the solid-angle measure of the half-power point of
the main lobe of the antenna pattern. The half-power beamwidth (HPBW) can be
measured by moving the telescope in a continuous scan across a very bright radio source.
Except for the possibility of Cygnus-X or certain geo-synchronous satellites, the only
source available to the SRT is the Sun.
Measurement of the beam pattern can help the user discover problems with
optical alignment or aid in the determination of the antenna focus.
Procedure:
The SRT has azimuth and elevation travel limits that will constrain the user
conducting the Sun scan to times close to local noon. This will allow maximum
offset from the sun in order to establish a stable baseline for the scans and an off-
source calibration position that will not be overpowered by the sun's brightness
temperature. For the off-source calibration, an area at least two beamwidths (in
azimuth, positive or negative) away from the sun is desirable.
A sample command file for the Horizontal (Azimuth) then Vertical (Elevation)
scans might look like this (note: commands for the analog receiver are colored
blue):
: record filename /Start recording, output filename is optional
: azel 130 45 /calibration position
: 1415 5 0.0 /scan frequency, 5 bins (samples), no frequency step
: 1415.0 /center frequency with mode 1, 500MHz bw (default)
: calibrate /calibration using vane calibrator
: noisecal /when using noise source (either vane OR noise)
: Sun /Source command
* Azimuth Scan /Comment
: offset -30 0 /start offset commands for scan -30 to +30 degrees
: offset -29 0
: offset -28 0
: offset -27 0
: offset -26 0
: offset -25 0 /through to offset 30 0
* Elevation Scan /Comment
: offset 0 30 /Start elevation scan (if sun El is <60 degrees!)
: offset 0 29
: offset 0 28
: offset 0 27
: offset 0 26
: offset 0 25 /through to 0 -30
: roff /End recording