[Antipodal]

Hi everyone,

I am still wrestling with the front end of this set. On the schematic (which Chas helpfully put up )the aerial connector has  three terminals. One is labelled "A" ,  presumably for antenna . One is labelled "E" for earth. The one in the middle is labelled "Z".Can anyone tell me what "Z" stands for? 
Also, on the  printed paper schematic there is a dotted line shown between "Z" and earth terminals. This dotting is not clear on the schematic Chas has uploaded but it  ( the dotted line between "Z" and earth on the paper schematic)has me confused. Can anyone throw light on  this dotting?Does it mean that a busbar should /could be put between "Z" and earth and if so under what conditions? 
Thanks everyone and cheers.