[Drake] dummy plug for R4C

[DJED1 at aol.com]

I don't think the receiver works at all without the dummy plug.   It sounds 
like you need to jumper the external mute RCA jack on the back of the receiver. 
  If this plug is missing, the radio will work OK except on the settings of 
"ext mute", "NB", and "CAL".   
Ed