Let's talk DSL signal strength: Why does my signal level degrade over a few hours?

Factual Questions
1

It’s happened again.

I’m at home, but I’m on call this week, so as usual I"m keeping my computer turned on and logged into the office so my email rules will work. (That is, I need to have my email on so if I get any failure notices, they’ll be forwarded to my BlackBerry. (It’s a temporary situation–never mind about that)).

Anyway. When I first turn on the computer, the signal from my router is ‘excellent’. Then over time it degrades to ‘very good’, then ‘good’, and then ‘fair’. Usually, if the computer is in the living room, that doesn’t happen, but it usually does in the bedroom, so much so that I can’t work there. The reason for that is that the network at the office seems to have some threshold of signal quality under which it automatically disconnects itself.

What causes the router signal to degrade? Tonight I was practicing on my electric guitar, near the computer. I wasn’t using an amplifier, but there are certainly magnets in the pickups; could they have caused the degradation? Or could I have hitchhikers? I don’t see how that’s possible; there’s a security code that they would have to enter to be able to use my router, and how could they know that?

2

As I wrote that, it went from excellent to good. The router is about two feet behind me in the second bedroom. There’s a wall between me and it, of course, but since when is that supposed to be a problem?

3

Modems constantly monitor the state of the signal and “back off” on the speed when it notices degradation. There are supposed to then ramp back up when the quality goes back up. Some modems are not very good at the latter. So a tiny blip causes it to slow down for an untoward amount of time. Several spaced out small blips and it really slows down.

The blips can be anywhere between you and the switching center. E.g., a car with bad plugs a couple blocks away passes next to the cable.

You can try resetting the modem to get it back to top speed. On some modems the best way is to power-cycle.