Need half-duplex on console

hi all

first, sorry for my bad english.
I have a little problem with my Asterisk server.
I would like to turn on a half-duplex mode.I phone
via console through the speakers. Now, the conversation-partner
have always a strong echo of himself.I call via a SIP trunk.
So, is there a way to change the communication over the console in a half-duplex mode…? like the
"# define AGGRESSIVE_SUPPRESSOR"-Parameter in zaptel…?

I use Astersk-1.6.x …

thx for any help!