Bueno, podemos escribir:
$$ \ mathscr {H} \ left (\ text {s} \ right): = \ frac {\ frac {1} {\ frac {1} {\ text {R} _1 + \ text {s} \ text {L}} + \ frac {1} {\ left (\ frac {1} {\ text {s} \ text {C}} \ right)}}} {\ text {R} _2 + \ frac {1} {\ frac {1} {\ text {R} _1 + \ text {s} \ text {L}} + \ frac {1} {\ left (\ frac {1} {\ text {s} \ text {C} } \ right {}}} = = frac {\ frac {\ text {R} _1 + \ text {L} \ text {s}} {1+ \ text {C} \ text {s} \ left (\ text { R} _1 + \ text {L} \ text {s} \ right)}} {\ text {R} _2 + \ frac {\ text {R} _1 + \ text {L} \ text {s}} {1+ \ text {C} \ text {s} \ left (\ text {R} _1 + \ text {L} \ text {s} \ right)}} \ tag1 $$
Deje que \ $ \ text {s}: = \ omega \ cdot \ text {j} \ $ where \ $ \ text {j} ^ 2 = -1 \ $:
$$ \ left | \ mathscr {H} \ left (\ omega \ cdot \ text {j} \ right) \ right | = \ left | \ frac {\ frac {\ text {R} _1 + \ text { L} \ text {s}} {1+ \ text {C} \ omega \ text {j} \ left (\ text {R} _1 + \ text {L} \ omega \ text {j} \ right)}} { \ text {R} _2 + \ frac {\ text {R} _1 + \ text {L} \ omega \ text {j}} {1+ \ text {C} \ omega \ text {j} \ left (\ text {R } _1 + \ text {L} \ omega \ text {j} \ right)}} \ right | = \ frac {\ frac {\ left | \ text {R} _1 + \ text {L} \ omega \ text {j} \ right |} {\ left | 1+ \ text {C} \ omega \ text {j} \ left (\ text {R} _1 + \ text {L} \ omega \ text {j} \ right) \ right |} } {\ left | \ text {R} _2 + \ frac {\ text {R} _1 + \ text {L} \ omega \ text {j}} {1+ \ text {C} \ omega \ text {j} \ left (\ text {R} _1 + \ text {L} \ omega \ text {j} \ right)} \ right |} \ tag2 $$
En resonancia (usando los valores en su esquema):
$$ \ text {f} _0 = \ frac {10000} {94 \ pi} \ cdot \ sqrt {6000 \ cdot \ sqrt {6140388085} -54289} \ approx734.213 \ space \ text {kHz} \ tag3 $$
Y:
$$ \ left | \ mathscr {H} \ left (2 \ pi \ cdot \ text {f} _0 \ cdot \ text {j} \ right) \ right | \ approx0.668602 \ tag4 $$
Usando Mathemactica, obtuve para \ $ \ left (2 \ right) \ $ usando tus valores: