The Nancay Radioheliograph (NRH; located at 47 N 02 E)
provides since the end of 1996 two dimensional images of the radio
brightness of the Sun with second time resolution. It consists of
two linear antenna arrays, on terrestrial east-west and north-south
baselines respectively. In its earlier versions it operated in 1D
only at 169 MHz with both arrays from 1980 until early 1985, and
later at 164 MHz with the east-west array, and in a five-frequency
mode with the north-south array from 1986 to 1990. Since late summer
1991 both arrays of the NRH are operated in the multifrequency mode.
Up to five frequencies are chosen in the range 150 - 450 MHz within
the restrictions imposed by terrestrial interference. Since the end
of 1996, N/S and E/W arrays can be correlated in the multifrequency
mode from 150 to 450 MHz in order to produce 2D radiograms.