When using high speed USB devices such as CCD and CMOS imaging cameras over long cables, you need to have optimum USB signal integrity. This means: Use a high quality cable - if in doubt, buy a brand new high quality cable (not a cheap one!) Do not exceed the recommended cable length: 3 meters / 10 feet for USB 3.0 5 meters / 16 feet for USB 2.0 Do not use the front panel USB jacks on desktop computers. The internal computer wiring has already degraded the signal quality before it gets to the jack! Almost all manufacturers use cheap wiring and connectors internally, resulting in impedance discontinuities that cause signal reflections. Long cables make the reflections much worse, degrading signal integrity and causing data errors. This is often bad enough to make the interface fail completely or at least act glitchy. You can get away with a memory stick because it has a zero-length cable. A short cable to a portable hard drive will also probably work okay. A maximum length cable running at high speed will work marginally if at all. Watch out for USB hubs: Inexpensive desktop hubs use cheap ceramic resonators for their frequency reference (they're literally just a few cents cheaper than an ultra-stable quartz crystal). These resonators are very temperature sensitive and go off-frequency in winter conditions! This causes endless problems with data reliability - and users often don't recognize the correlation with cold temperatures. Use only a high quality, industrial hub rated for wide temperature range. Try to avoid connecting a camera through a hub shared with other equipment. The data volume on cameras is extremely high, and the single channel going back to the computer may not be able to keep up. I've personally seen a camera and autoguider combination fail in this situation - every time the main camera downloaded, the autoguider failed - and vice-versa! Cameras and autoguiders should have their own dedicated USB connection. Everything else can run on a hub. Note that computer USB ports tend to come in pairs, and those pairs share a root hub inside the computer. So in some cases high traffic on one connector may affect its neighbor.
