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Re: [Fwd: Re: LAN noise?]



Hi Glenn,

The net "current flow" through the ferrite should be quite small...
ideally negligible.  The ferrite will choke common mode noise, but should
have little effect on the differential modulation used by 10BASE-T etc.

I wonder whether Franklin is running 10 or 100Mbps, and if he has any specs
on the ferrites used. It would be an interesting test to place a ferrite or
two on some CAT-5, and then measure its performance using a LAN cable
tester...  maybe I'll do just that sometime next week.

Of course, fibre would be even better .... :-)

73 Chris



At 04:58 PM 01/06/1999 -0400, you wrote:
>Data over a CAT 5 cable is high speed.  Ferrites impede changes in
>directio on current flow.  The higher the speed the more the impedement
>of change, up to the point of saturating the ferrite.  If the ferrite is
>to be efficient in eliminating radiated lAN noise, it will also be
>efficient at reducing the amplitude on the LAN.  This may be ok for very
>short distances, but, over a longer distance the signal may be
>attenuated enough to cause errors.  At the least the nice square waves
>that the LAN card generates and looks for will become more like sine
>waves.
>
>Glenn
>WB4UIV
>
>
>Franklin Antonio wrote:
>> 
>> At 09:21 AM 6/1/99 -0400, Al Lawler wrote:
>> >I used to get RF pickup from the keyboard, but that eas easilly cured with
>> >a ferrite bead,  although this would probably degrade the performance of a
>> >lan cable...)
>> 
>> In my experience, twisted pair LAN cables work just fine with ferrite beads
>> on them.  When I wired my house, I put ferrite beads around the cat-5 cable
>> behind every wall jack.  I also put them on the cables at the hub end
>> before I crimped on the connector.  I bought a huge bag of ferrite beads at
>> a swapmeet once that fit nicely over the cat-5 cable.  Also fit nicely over
>> the burglar alarm cables.
>> 
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