The Josephson effect in point contacts between an “ordinary” superconductor $$\hbox {Pb}_{0.6}$$
Pb
0.6
In$$_{0.4}$$
0.4
($$T_c \approx 6.6 \, {\mathrm {K}}$$
T
c
≈
6.6
K
) and single crystals of the Fe-based superconductor Ba$$_{0.6}$$
0.6
K$$_{0.4}$$
0.4
(FeAs)$$_2$$
2
($$T_c \approx 38.5 \, {\mathrm {K}}$$
T
c
≈
38.5
K
), was investigated. In order to shed light on the order parameter symmetry of Ba$$_{0.6}$$
0.6
K$$_{0.4}$$
0.4
(FeAs)$$_2$$
2
, the dependence of the Josephson supercurrent $$I_s$$
I
s
on the temperature and on $$\sin (d\varphi )$$
sin
(
d
φ
)
with $$d = 1, 2$$
d
=
1
,
2
was studied. The dependencies of the critical current on temperature $$I_c (T)$$
I
c
(
T
)
and of the amplitudes of the first current steps of the current–voltage characteristic $$i_n^{exp} (\sqrt{P})$$
i
n
exp
(
P
)
$$(n = 0, 1, 2)$$
(
n
=
0
,
1
,
2
)
on the power of microwave radiation with frequency $$f = (1.5 \div 8)\, {\mathrm {GHz}}$$
f
=
(
1.5
÷
8
)
GHz
were measured. It is shown that the dependencies $$I_c (T)$$
I
c
(
T
)
are close to the well-known Ambegaokar–Baratoff (AB) dependence for tunnel contacts between “ordinary” superconductors and to the dependence calculated by Burmistrova et al. (Phys Rev B 91, 214501 (2015)) for microshorts between an “ordinary” superconductor and a two-band superconductor with $$s \pm$$
s
±
order parameter symmetry at certain values of the transparency of boundaries and thickness of the transition layer. It is found that the dependencies $$i_n^{exp} (\sqrt{P})$$
i
n
exp
(
P
)
cannot be approximated within the resistively shunted model using the normalized microwave frequencies $$\Omega = 2 \pi f / (2eV_c / \hbar )$$
Ω
=
2
π
f
/
(
2
e
V
c
/
ħ
)
with characteristic voltages $$V_c = I_c R_N$$
V
c
=
I
c
R
N
, $$(R_N$$
(
R
N
—normal resistance of the contact) found from the low-voltage parts of the current–voltage characteristics. The reasons for this failure are discussed and a method is proposed for accurately determining the value of $$\Omega$$
Ω
, which takes into account all the features of the point contact affecting the period of the dependence $$i_n^{exp} (\sqrt{P})$$
i
n
exp
(
P
)
. An analysis of the $$I_c (T)$$
I
c
(
T
)
and $$i_n^{exp} (\sqrt{P})$$
i
n
exp
(
P
)
dependencies shows that the superconducting current of the Josephson contacts under investigation is proportional to the $$\sin$$
sin
of the phase difference $$\varphi$$
φ
, $$I_s = I_c sin(\varphi )$$
I
s
=
I
c
s
i
n
(
φ
)
. The implications of these results on the symmetry of the order parameter are also discussed.