hi guys
I’m trying to set antenna A for this chipset that comes with 3com pci card ,
it shows -80 for Antenna jack A and again it shows -80 for antenna jack B.
which one is right?
God help me to choose the right jack 
Thanks
you can try to search for the wireless card specification to get more detailed information about the particular wireless card.
well the card specification is one thing.
what mikrotik is detecting is another thing.
Wireless card should work accordingly to the specifications.
P.S. As different wireless cards work accordingly to specification, first of all problem might be with your configuration (probably antenna was not connected properly or any other issues with antenna).
Second check the wireless card specification for the antenna port operating.