To touch on what PLuNK mentioned with the resistance - in order to provide maximum power transfer between the source and load, the source impedance and load impedance must match, otherwise it is a small fraction of the signal power transfered.
This can be a big problem in most 'DIY rigs'.
There are many solutions to impedance matching be it selecting right coax cable, baluns, etc.
Having a stronger Tx signal is great it can send data to a source over a longer distance than normal, but the Rx will need to have an increase in signal power if it wants to be able to successfully transmit back.
Is there many obstructions between the Rx and Tx? Is there clear line of sight?
Are there sources of interefence available (noise) which will effect the weak signal arrived at the Rx?
EDIT: Has he tried the parabolic antenna on the laptop? May be of use if he can not increase the SNR of his card.