On Sun, 10 Sep 2006 10:26:02 -0500, CARY GOOCH wrote:
>The other has an integrated antenna, 2 mile shot and taking so much
>interference from a 3KW FM Stereo antenna 40 feet higher up the tower
>that I can not even log into it (power over Ethernet, shielded cable
>with drain wire.
You're on the wrong list for this kind of question. Check out the RFI
list, also on contesting.com.
BUT: Since I'm an RFI guy and have wrestled with this kind of problem,
here are several thoughts. First, that cable shielding does nothing good
and may CAUSE problems if it is not bonded to the right point, which
must be the shielding enclosure of the equipment at each end. With most
Ethernet equipment, it can be next to impossible to find the shielding
enclosure, especially via a path that is short at the frequencies of
interfering signals. See the tutorials on my website about "the pin 1
problem," and think of it in the context of your equipment.
Second, most Ethernet gear I've run into couples RF common mode on the
Ethernet cables -- that is, it both sends and receives RF lengthwise on
the Ethernet cable acting as a long wire antenna. The solution to that
mode of coupling is a suitable ferrite choke. There are HUGE differences
in ferrite chokes, and you may need multiple ferrite parts to get
sufficient choking impedance. See the applications note on
"publications" section of my website.
Third, remember that Ethernet is 2-way, so both ends of the cable
transmit and both receive. This means that both ends are susceptible, so
both ends may need chokes if the cable is longer than about 1/10
Fourth, remember that trash can also couple via power supply leads. In
your case, that would be the power supply leads at the equipment that
communicates with your POE equipment.
Fifth, RF can couple via inadequate shielding of equipment -- that is,
the internal wiring acts as antennas. Equipment may APPEAR to be
shielded, but there may be gaps in the bonds between pieces of the
enclosure (for example, paint can get in the way, and there may be slots
big enough to let the RF in).
Jim Brown K9YC
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