  Experimental data on signal and noise characteristics of high--$T_c$ RF
SQUIDs with large inductance of quantization loop are presented. The SQUIDs
were produced by a thick--film HTS--technique of painting on the Y$_2$BaCuO$_5$
substrate. For the first time, a steady quantum interference was observed in RF
SQUID with the inductance as large as $L_S=6.6$ nH, that is, 60 times higher
than the fluctuation inductance $L_F\simeq10^{-10}H$ at the liquid nitrogen
temperature T=77 K. A new method is offered to evaluate the sensitivity of RF
SQUID with optimum inductance of the quantization loop.
