This is a BASIC connection for CW,RTTY,SSTV,APRS,Amtor,Packet,Psk-31 ect ..
Many users modify the above circuit to include
isolation transformers within the Speaker out
and Line-in or microphone in lines.
These isolation transformers are used to preclude ground loops within a
system from introducing hum and interference on the transmitted signals.
1 x Red
1k : 8ohm
1 x Blue 3k : 3k