  The radio emission during 201 X-ray selected solar flares was surveyed from
100 MHz to 4 GHz with the Phoenix-2 spectrometer of ETH Zurich. The selection
includes all RHESSI flares larger than C5.0 jointly observed from launch until
June 30, 2003. Detailed association rates of radio emission during X-ray flares
are reported. In the decimeter wavelength range, type III bursts and the
genuinely decimetric emissions (pulsations, continua, and narrowband spikes)
were found equally frequently. Both occur predominantly in the peak phase of
hard X-ray (HXR) emission, but are less in tune with HXRs than the
high-frequency continuum exceeding 4 GHz, attributed to gyrosynchrotron
radiation. In 10% of the HXR flares, an intense radiation of the above genuine
decimetric types followed in the decay phase or later. Classic meter-wave type
III bursts are associated in 33% of all HXR flares, but only in 4% they are the
exclusive radio emission. Noise storms were the only radio emission in 5% of
the HXR flares, some of them with extended duration. Despite the spatial
association (same active region), the noise storm variations are found to be
only loosely correlated in time with the X-ray flux. In a surprising 17% of the
HXR flares, no coherent radio emission was found in the extremely broad band
surveyed. The association but loose correlation between HXR and coherent radio
emission is interpreted by multiple reconnection sites connected by common
field lines.
