On 30th June 1989 high sensitivity-spectral resolution observations of solar radio bursts were carried out in the frequency range of 18 - 23 GHz. The burst observed at 17:46 UT was different from the 60 bursts observed so far in the sense that it exhibited a frequency fine structure superimposed on the ongoing burst in its rising phase, i.e. an additional enhancement of the flux density of the order of 10 SFU, observed only in the 21 and 22 GHz frequency channels, lasting for about 4 s. Interaction of an emerging loop with an adjacent loop accelerated particles in that loop from which the broadband burst was emitted due to the gyrosynchrotron emission. The observed fine structure is interpreted as due to thermal gyro-emission at 6th harmonic of the gyrofrequency originated from a hot kernel with short lifetime located at the top of emerging loop. We derived the hot kernel source parameters, th e temperature as 8 <FONT FACE="Symbol">´</font>10(7) K, the magnetic field as <img src="http:/img/fbpe/bjp/v29n3/510i1.gif" alt="510i1.gif (46 bytes)"> 1250 G and the density as <img src="http:/img/fbpe/bjp/v29n3/510i1.gif" alt="510i1.gif (46 bytes)"> 5 ×10(12) cm-3.