In order to estimate self- and mutual inductances of the input coil and the
pick-up loop of a YBCO SQUID amplifier operating at 77K, a simple method b
ased on the determination of the current and flux distributions into the su
perconductors is presented. The cases of inductors (single loop and spiral)
and induced circuits (closed and open loop) are considered, The authors st
ress the difference between a SQUID pick-up loop and a directly coupled mag
netometer depending upon their action on the input inductance. Finally, the
coupling efficiency and the ground plane effect are calculated and measure
d for various patterns.