fed up with my wifi card

i have asus f81se with atheros 928x
router 3com office connect with 11g wireless module
the problem...the router is in my room but when i move like 15 meters away not in front of it but within a nearby room or the balcony the signal drop to 40% and my speed goes up and down
is this normal..or its just my card sucks compared to intel cards
and also i wanna full specification of that card i didnt find it over the internet
another thing... is it possible to change it with intel one despite that particular model comes with atheros?

 

IMO 15 meters away through walls on a wireless g network is going to kill some of the signal. Then again, I don't know what is in your walls.
In my netbook I have the Atheros AR9285 and I don't have any problems with my wireless coverage, but my networks at home and work are wireless N. At work I have been as far as about ~75 feet away through several walls and managed to get through.

 

50-60% drop in signal strength, through 1-2 walls, at 15 meters (45 feet) can be normal on 11g, esp if the outer walls are brick or inside are insulated gypsum/sheetrock. Performance speed fluctuation when the signal is <50% are common and likely dip pretty low on occasion. Plus, 802.11g typically suffers pretty serious drops and is prone to performance issues as soon as the signal has to start going through anything and this is compounded when there is more than 1 surface the signal is going through.

OP may want to post a new thread asking about the possibility of the wireless replacement as it's likely to get picked up by the members for answer easier.

This issue of signal strength and performance has just as much to do with the wireless router as the notebook module, however, so the notebook is not the sole culprit here.