Cannot see own network in available networks

This is not really a problem but a question:

I have a notebook and desktop connected to a wireless network. My own
network and neighbouring networks can be seen in the 'available networks'
window of my notebook, but in the same window of my desktop only neighbouring
networks can be seen but not my own. It can only be seen below in the left
hand column. The connection works fine, I just wonder why my own network is
excluded from 'available networks'. Thanks - Louis