[mythtv-users] OT: USB inductance (or other) problems with external peripherals

Stephen P. Villano stephen.p.villano at gmail.com
Tue Oct 15 19:29:45 UTC 2013


On 10/15/13 10:45 AM, Raymond Wagner wrote:
> On 10/15/2013 10:25 AM, Stephen P. Villano wrote:
>> It isn't always impedance causing a problem, especially with USB. USB
>> uses a lower frequency than gigabit ethernet.
>> But, one can suffer from ringing on long runs, secondary to
>> inductance in the line.
>> That is why many long length USB cables come with built in Schmitt
>> triggers as buffers.
>
> Define "long runs", as you're not allowed to have a USB cable longer
> than 16'.  The only ethernet runs I have that short are the ones in my
> basement, to devices mounted on the same wall as my switch.
> _______________________________________________
I have 16 footers, they're all active cables with buffer circuits
(pretty much Schmitt triggers) to eliminate ringing caused by the
inductance of the long cable.
Needless to say, 16 feet is a long run for USB.
That said, there are longer active cables available.
http://www.amazon.com/PTC-Meters-Extension-Repeater-Supports/dp/B0040IASMS
is one example. 20 meters worth of example.
If it didn't have the buffer circuit, it'd be useless.


More information about the mythtv-users mailing list