[RTTY] Using a 4-conductor laptop audio jack to decode RTTY

[Dennis]

I have a laptop that uses a 4-conductor jack for audio.  I have the correct
adapter, but I can't get it to decode an audio stream.  Even though I have
the correct adapter (I know because an electret microphone works FB
when I connect it to the adapter jack), when I connect the audio cable
from the radio the laptop reacts like there is nothing plugged in to the 
jack.

 From memory, it seems to me that the way to solve this is to use a resistor
across the microphone line so that there is some current drawn thru the
mike line, because the laptop uses that current draw to signal that a mike
has been plugged into the laptop, but I can't find any references on the
web.  Can someone help me out with this?

Thanks.

Dennis W1UE