Hi
Good points as always from PhilipD. I believe now I come to think of it that we have discussed this before and my errors have been illustrated earlier. I would think though that modems’ circuit boards may vary in the quality of their design in this respect. Is that reasonable?
The quality definitely differs, some will be obviously worse and identifiable from sync speed and other statistics about the line and comparable if based on the same chipset, but then things like firmware versions of the modem code come into play. I would think most are pretty close enough that other affects will mast differences, for example slight differences in the circuit design might favour one VDSL line over another.
Anyone got a biscuit tin and some tools?
Just place it in a biscuit tin and run the wires out the top and loosely replace the lid will do just as well. This will shield the modem from any external interference, but of course it depends if that noise is entering via the plastic case into the circuit board directly, or being picked up by the power supply wire and telephone line, and so if the latter, it will make no difference.
It's also unlikely the circuit board is picking up external interference that is causing any negative results, as they have to be designed to be tolerant to external noise to comply with regulations, and also the circuit board will be designed with ground planes and the circuit tracks are always short and so would not really act as an antenna to many frequencies.
I have my modem surrounded by lots of kit all within a few feet, a pfSense box, a small fanless PC, a Philips Hue bridge, a Wi-Fi access point, a network switch and DECT cordless phone. Underneath the modem shelf are all the power supplies for all the kit, yet I can turn everything off, shut the house mains power off and run the modem on it's own via a UPS, and SNR margin is unchanged, despite the modem being in a plastic case.
I wonder if some washing machines have a temperature sensor in them that detects when the motor is melting. That's what happened when our washing machine started belchin out toxic smoke when we lived in london, luckily Mrs Weaver was around at the time. My good friend in Yorkshire had some white-goods type appliance catch fire and wrecked the house with smoke damage. When our house in Skye had a kitchen fire over ten years ago it was possibly a central heating pump that melted, not sure. Perhaps I should patent yet another of my half-baked ideas.
You can get thermal fuses
http://uk.rs-online.com/web/c/fuses-sockets-circuit-breakers/fuses/non-resettable-thermal-fuses/ however very few electrical appliances have them. They have some problems, they are fairly costly, and need a manual process to install them as they can't be soldered in an oven with the rest of the components as that would fuse them, and they can't be soldered easily by hand as the heat would conduct up the leads and fuse them. So it's a case of crimping them in some how. Also they may not react quickly enough if the source of the heat isn't close by.
Regards
Phil