The table below summarizes efficiency data taken by the IRAM 30m staff in the period between March and August 1994. These data update and extend the comparable list of efficiencies presented in Newsletter No. 5 (September 1992). Measurements with the 1.3mm G2 SIS receiver are still pending.
While the forward efficiencies were deduced from skydips, the aperture
and main beam efficiencies and the half power beam widths were
derived from continuum cross scans on Mars and Uranus. The planetary
diameters during this period ranged between 
and 
.
Beam and aperture efficiencies are corrected for the theoretical
antenna gain-elevation dependence; this correction is at most 7%
for this data set. The values for the continuum sensitivity are on
the 
scale (flux per Kelvin = 3.906
for the 30m telescope).
From the scatter of the day-to-day measurements we estimate errors of
the efficiencies to be about 
%. We will continue to monitor
the efficiencies.
The product of measured beam widths and frequency is nearly constant
for frequencies up to 270 GHz. This indicates a constant
illumination of the subreflector independent of the receiver. The
good agreement allows to give a formula which may be used to
estimate the beam width to an accuracy of about 
between 90 and
270GHz:
30m Telescope Efficiency Data (November 1994)
Note: The conversion from antenna temperatures 
to
main beam brightness temperatures 
can be done via
. We use
the nomenclature of Downes, ``Radio Astronomy Techniques'', IRAM
preprint 151 (also in Evolution of Galaxies, Astronomical
Observations, Springer 1989).
Carsten KRAMER and Wolfgang WILD