Hi Volvic,
Firstly

to CF.
When the disconnects happen, what are the status of the Modem lights.
And when these disconnects happen if you have an Ambit CableModem (silver type) you can check the power levels at the point it disconnects by pointing your browser to 192.168.100.1 (user - root, password - root).
Post back with the light status and the signal levels.