I've been playing with a Motorola Canopy wireless broadband system and I'm going to share some of the info I've found.
I've got an 5.7 Subscriber unit (SU) that takes .36 Amps at 18.03 Volts. Thats 6.48 Watts.
The units will work with 6.5V/1A supplies but you need to provide 6.5 Watts and they may stop working at lower tempertures. It would be an ok voltage for a test rig but I wouldn't install a customer device with that low of voltage.
The Canopy uses a standard LM2596 regulator to drop whatever you give it to 5 Volts. That means any extra voltage gets converted into heat. The longer longer the run, the higher the voltage loss in the cable. At 300 ft your getting several volts drop. Notice how warm the Canopy's get? Your cable it getting that much energy too but is spread out. Thicker conductors will help reduce losses. The regulator needs at least 6.3V on a cold day to make the 5v that the logic needs. I expect theres at least one diode in there as well so that adds a .8v more or so. The Canopy power supply seems to be identical to the one used for the 3com nbx ethernet phone system excpet the polarity is around the other way. Makes it fun for testing at work were we have a "power over ethernet--nbx standard". Cisco's standard uses +/- 48 V and there are a few others as well which is too much for the National regulator.
10baseT Ethernet is speced at 100m (328 ft) but will work on longer distances based on how good the gear is on both ends. The ethernet stats will show you if there are problems. Things like any CRC errors or RxOverrun or LateCollision indicate that the two ends aren't quite talking but thats mostly an issue for 10mb half duplex. Keep in mind if you push your luck and try to go over the specs, it may stop working as some as one end warms up or cools down a bit.
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