too much PING after change antennas....

Hi everyone.

I have recently install Mikrotik 2.9.6 in a P166 Mhz whit 64 Mb Ram EDO and a Triton II motherboard. It has two isa 3com ethernet and two DWL-G510 atheros based cards.

The thing is that i have one of the atheros ( the one that its working as an acces point ) whit a DHCP Server defined and it works fine. Each one of the clients can connect to the node and automatically retrieve an IP.

The problem appears when i change the antennas. Normally i used a small 2dbi antenna ( the one that comes whit the adaptor ) to make tests inside my house. But when i put a larger antenna ( a Trevor Marshall 8, 180ยบ whit 15dbi +/- gain ) and then back to the smallest one, it starts to have serious conectivity problems, whit over a 40 % of lost packets and too much latency ( like 800ms to 1130ms ).

What could it be ?

Any ideas. ?

use 2.9.12 please