Sony DAV-C450 Operating Instructions Manual page 22

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If you have poor FM reception
Use a 75-ohms coaxial cable (not supplied) to connect the system to an outdoor FM antenna as shown below.
Outdoor FM antenna
Note
If you connect the system to an outdoor antenna, ground it to protect against lightning. To prevent a gas explosion,
do not connect the ground wire to a gas pipe.
GB
22
System
Ground wire
(not supplied)
AM
COAXIAL
FM
75Ω
To ground