NATIONAL RADIO ASTRONOMY OBSERVATORY

Green Bank, West Virginia

DATE:

TO: VLBI Network

FROM: R.J. Maddalena

SUBJECT: NRAO-GB 140-ft telescope calibration, 1.67 GHz, September 1992

Calibration of Antenna Efficiency

The temperatures used throughout the calibration of antenna efficiency, eta _A, were determined from 70 pointing and source temperature measurements obtained during the VLBI session. I have used the assumed flux densities given in Table 1 and the measured antenna temperatures to estimate eta_A (when the physical aperture of the telescope is used eta_A equals 1.93 T_A/S where S is the 1.67 GHz flux in Jy.). At 18 cm, efficiency does not change with position in the sky for the 140-ft.

The average of the derived eta_A, 0.580ą0.003, is extremely close

to what has been derived in the past.

Table 1

Source Flux Density (Jy)

0023-26 7.76 ą 0.62 (2)

0237-23 6.32 ą 1.31 (2)

1245-197 5.08 ą 1.76 (2)

2021+61 2.23 ą 0.18 (1)

2203-18 6.05 ą 0.26 (1)

3C123 42.4 ą 2.6 (3)

3C161 16.8 ą 1.2 (3)

3C218 36.8 ą 4.4 (3)

3C231.0 7.57 ą 1.28 (2)

3C273 45.5 ą 1.9 (1)

3C274 184. ą 20. (3)

3C286 13.6 ą 0.9 (3)

3C295 19.2 ą 1.5 (3)

3C330 5.81 ą 0.92 (2)

3C348 37.5 ą 5.5 (3)

3C433 10.7 ą 0.8 (2)

3C438 5.66 ą 0.45 (2)

3C454.3 12.9 ą 0.56 (1)

3C48 13.9 ą 1.0 (3)

NGC 7027 1.60 ą 0.10 (1)

References:

(1) Previous reports on the calibration of the 140-ft telescope.

(2) Kuhr et al. (1981, Astr. Ap. Suppl., 45, 367).

(3) Baars et al. (1977, Astr. Ap., 61, 99).