[SI-LIST] Re: High speed USB cable

Yes - Meeting Class B with a USB cable attached
IS feasible. First things first...

Have you followed all the USB guidelines (such as
adding a CM choke in the signal lines)?

Best Regards
Charles Grasso
Compliance Engineer
Echostar Communications Corp.
Tel: 303-706-5467
Fax: 303-799-6222
Cell: 303-204-2974
Pager/Short Message: 3032042974@xxxxxxxxx
Email: charles.grasso@xxxxxxxxxxxx
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Bharathkumar Raju
Sent: Thursday, January 17, 2008 6:03 PM
To: Signal Integrity
Subject: [SI-LIST] High speed USB cable

What charecteristics the high speed USB cable must have to pass FCC
Class B radiated emissions? We cannot add a ferrite core to the cable to
supress the emissions. The device is a self powered high speed (480 MHz)
USB device. From various testings it is established that the CM curent
flowing through the D+ & D- conductors of the USB cable causing the
failures in the radiated emission testing. The tests also established
that the CM current flowing through the 5.0 volts +ve & -ve conductors
of the USB cable is not at all contributing for the emissions.
              Is it feasible to have a high speed USB bus powered device
with 1.5 m long USB cable to meet FCC / CISPR ClassB radiated emission
limits (without a ferrite core attached to it).=20
Bharath

PS : I hope this question is appropriate for this forum..


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