What sort of computer is in the observatory?
If it's a desktop, does the network card have ONE external antenna that you can unscrew?
If so, I'd recommend trying this
LINK
You can get extensions to go between the antenna and the computer - ideally you'd mount the antenna on the outside of the observatory.
I've got a couple of these, one for home and one at Leyburn. I can pickup a signal over 50metres across the paddock. The routers use their standard antennae.
If the network card has multiple antennas, you might need to look for something a bit fancier.
DT