Sony AVD-S50 Operating Instructions Manual page 21

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If you have poor FM reception
Use a 75-ohms coaxial cable (not supplied) to connect the receiver to an outdoor FM antenna as shown below.
Outdoor FM antenna
Note
If you connect the receiver to an outdoor antenna, ground it to protect against lightning. To prevent a gas explosion,
do not connect the earth wire to a gas pipe.
Receiver
Earth wire
(not supplied)
AM
FM
75
COAXIAL
ANTENNA
To earth
GB
21