You should be able to find a supplier of ferrite beads on google. They
are
relatively inexpensive and you may have some in your attic of inventory
that
you didn't even realize. It sounds like you have eliminated other
thoughts
I had.
What are the bumps at the end of computer cables?
In a typical computer system found in a home or office, you normally see
these "bumps" on the mouse <http://www.howstuffworks.com/mouse.htm> ,
keyboard <http://www.howstuffworks.com/keyboard.htm> and monitor
<http://www.howstuffworks.com/monitor.htm> cables. You can also find them
on power supply wires when a device (like a printer
<http://www.howstuffworks.com/inkjet-printer.htm> or scanner
<http://www.howstuffworks.com/scanner.htm> ) uses an external transformer.
These "bumps" are called ferrite beads or sometimes ferrite chokes. Their
goal in life is to reduce EMI (electromagnetic interference) and RFI
(radio-frequency <http://www.howstuffworks.com/radio-spectrum.htm>
interference). You can see these beads in the following photo:
A ferrite bead is simply a hollow bead or cylinder made of ferrite, which
is
a semi-magnetic substance made from iron oxide (rust) alloyed with other
metals. It slips over the cable when the cable is made, or it can be
snapped
around the cable in two pieces after the cable is made. The bead is
encased
in plastic -- if you cut the plastic, all that you would find inside is a
black metal cylinder.
Computers <http://www.howstuffworks.com/pc.htm> are fairly noisy devices.
The motherboard <http://www.howstuffworks.com/motherboard.htm> inside the
computer's case has an oscillator
<http://www.howstuffworks.com/oscillator.htm> that is running at anywhere
from 300 MHz to 1,000 MHz. The keyboard has its own processor and
oscillator
as well. The video card <http://www.howstuffworks.com/graphics-card.htm>
has its own oscillators to drive the monitor. All of these oscillators
have
the potential to broadcast radio <http://www.howstuffworks.com/radio.htm>
signals at their given frequencies. Most of this interference can be
eliminated by the cases around the motherboard and keyboard.
Another source of noise is the cables connecting the devices. These cables
act as nice, long antennae for the signals they carry. They broadcast the
signals quite efficiently. The signals they broadcast can interfere with
radios and TVs <http://www.howstuffworks.com/tv.htm> . The cables can also
receive signals and transmit them into the case, where they cause
problems.
A ferrite bead has the property of eliminating the broadcast signals.
Essentially, it "chokes" the RFI transmission at that point on the
cable --
this is why you find the beads at the ends of the cables. Instead of
traveling down the cable and transmitting, the RFI signals turn into heat
in
the bead.
These links will help you learn more:
* Using
<http://www.howstuffworks.com/framed.htm?parent=question352.htm&url=http://w
ww.antennex.com/shack/Dec99/beads.htm> Ferrite Beads
* Dealing
<http://www.howstuffworks.com/framed.htm?parent=question352.htm&url=http://w
ww.repairfaq.org/REPAIR/F_comprfi.html> with Computer generated RFI/EMI
* EMI
<http://www.howstuffworks.com/framed.htm?parent=question352.htm&url=http://w
ww.steward.com/techinfo/subsystems.html> Control Applications Notes
* How <http://www.howstuffworks.com/radio.htm> Radio Works
* How Oscillators Work <http://www.howstuffworks.com/oscillator.htm>
Respectfully,
Rick Harnish
President
OnlyInternet Broadband & Wireless, Inc.
260-827-2482
Founding Member of WISPA
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Mike Hammett
Sent: Tuesday, May 29, 2007 4:37 PM
To: WISPA General List
Subject: Re: [WISPA] Ethernet problems
The only location where power might be parallel to the cable is in the
basement, but all of the power cables there (IIRC) are ran in metal
conduit.
This unit is the only thing functioning on the tower. There is a TV
antenna, but he couldn't get the signal he was wanting, so it isn't hooked
up at this time (perhaps an opportunity to figure that out for him).
The enclosure is a RooTenna, so a metal back with metal mounting hardware
to
the metal tower, plastic sides and front. There is an FM tower a mile and
a
half away, but I have 5 installations closer than this with no problems.
I have not tried ferrite beads because I know nothing about them. Not how
they work, how to install, where to obtain, how to troubleshoot, etc.
-----
Mike Hammett
Intelligent Computing Solutions
http://www.ics-il.com
----- Original Message -----
From: "Rick Harnish" <[EMAIL PROTECTED]>
To: "'WISPA General List'" <wireless@wispa.org>
Sent: Tuesday, May 29, 2007 3:22 PM
Subject: RE: [WISPA] Ethernet problems
Mike,
5
Is there 120v power running parallel to the cable? What else is on this
tower? Any high wattage RF transmitters? I have seen shielded cat5
interfered with to the point where we had to use fiber as the transport
up
the tower instead of cat5. Is the enclosure plastic or metal? Have you
tried ferrite beads?
Respectfully,
Rick Harnish
President
OnlyInternet Broadband & Wireless, Inc.
260-827-2482
Founding Member of WISPA
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Mike Hammett
Sent: Tuesday, May 29, 2007 4:11 PM
To: WISPA General List
Subject: [WISPA] Ethernet problems
I installed a customer in October and started having Ethernet problems in
March. I have an approximately 200' Ethernet run from the top of a TV
tower, to the house, and through the basement. I installed a Belden?
outdoor Cat5E cable, a Mohawk outdoor gel cable, a rope for future cable
additions, and an RG6 quad shield TV cable in a conduit.
Numerous times I cut off slack on both ends of the original cable (the
Belden). All that fixed the problem was turning off auto negotiation and
setting it to 100 HDX. A few weeks later the problems returned, and I
set
it to 10 HDX. Now, maybe 6 weeks later the problem is back. I switched
to
the Mohawk cable. I put on a different PoE injector and a different ECS
cable (PacWireless cable that provides an Ethernet jack on the outside of
the enclosure and has a 1' pigtail that plugs into the Mikrotik board.
Problem remains. The Mikrotik is getting power as it associates with my
tower and the two clients off an AP installed on the same board work just
fine. I tried different patch cables from the injectors to the
laptop\desktop.
I really don't want to pull 200' of cable only to have it not work again.
Does anyone have a good Ethernet tester I can borrow\rent? Not one that
just says if the pins make it (I had one of those and it said the cable
was
fine), but one that is a bit more advanced. From my understanding, these
are $800 - $5k units. Someone close to Northern Illinois would be best.
I'm out of ideas.
-----
Mike Hammett
Intelligent Computing Solutions
http://www.ics-il.com
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