Thank you Jim for that very informative and helpful message!
Ron, wb1hga
Jim Brown wrote:
> Proximity to the radio is meaningless. The following comments
apply to virtually ALL Ethernet devices, including your computers.
What matters are:
1) The antennas connected to the Ethernet device -- their length,
and their proximity to YOUR antennas (but NOT to your radio).
2) The design of the device with respect to SHIELDING of its own
internal wiring
3) The design of the device with respect to the internal
generation of RF trash
4) The design of the device with respect to keeping whatever trash
it produces off the antennas connected to it.
5) The directivity of the ham antennas and the Ethernet antennas.
MOST of the noise in the equipment I've tested comes out of the
box as a COMMON MODE signal, and is radiated by those cables as if
they were a long wire antenna. The good news is that the noise can
be greatly reduced by winding some turns of both the Ethernet
cables and the power supply cables around the RIGHT ferrite
toroids. Once you do that, you're left with what comes out of the
box due to poor shielding. And, of course, whatever is radiated by
your neighbors systems that are close enough to your radio
antennas to be loud enough to hear. [You can identify 10BaseT
Ethernet as the source by listening around 10,106 kHz, 10,120 kHz,
14,030 kHz, 21,052 kHz for strong carriers with some subtle
modulation. While we buy 100BaseT gear, it carries both 10BaseT
and 100BaseT traffic, and most routers and modems talk 10BaseT.
These carriers are not based on a clock with a tight frequency
tolerance, so every system is running on a slightly different
frequency. That's why, for example, you will hear carriers between
about 14,029 and 14,030.5 kHz.]
There is a detailed tutorial on ferrites on my website, along with
presentations I've done to a couple of ham clubs. All can be
downloaded as pdf files. No cost, no cookies.
http://audiosystemsgroup.com/publish
BTW -- shielded Ethernet cable doesn't help -- for the shield to
do anything, it would need to be connected at both ends, and you
would be hard put with these boxes to find a connection that meant
anything.
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