[mythtv-users] USB Hub Bandwidth limitations?

Brian Wood beww at beww.org
Wed Jul 8 01:55:27 UTC 2009

On Tuesday 07 July 2009 19:19:50 Lindsay Mathieson wrote:
> On Tue, 7 Jul 2009 18:53:56 -0600, Brian Wood <beww at beww.org> wrote:
> >> Additionally I guess the hub would need to be powered? or could an
> >> unpowered hub support 4 HD tuners?
> >
> > I'd think that as long as the tuners are self-powered (not drawing power
> > from
> > the USB port), you would not need a powered hub, but it couldn't hurt.
> Interesting - is there anyway to tell if a device is self powered?

If it has an external power supply or batteries it's probably self-powered. If 
the only source of power is the USB port it's probably not.

USB devices are supposed to draw only 500ma. (half an ampere), so they can 
have only 2.5 watts, though many devices draw more than that, in violation of 
the spec.

For example my Plextor PX-TV402Us have a "wall wart" type power supply, in 
addition to the USB connectors. It gets warm wnough that I suspect it draws 
more than 2.5 watts, which is why they made it self-powered.

Brian Wood
beww at beww.org

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