On Sun, 05 Feb 2006 15:40:39 +0100, Geert Jan de Groot wrote:
>0 mbit ethernet uses manchester encoding and hence only causes
>spectrum spikes every 5 Mhz (with sidebands, I know..)
Only on paper. 10BaseT ethernet puts out loud birdies on a number
of ham bands. I'm a CW guy, so I'll tell you about the ones that
I've identified. There are two on 30 meters, one around 14,030
kHz, another around 21,052 kHz, several around 28,015 kHz, and
some trash at the bottom of 6 meters. This stuff is generated in
the Ethernet devices (switches, hubs, routers, etc.) if there is
10BaseT traffic. Most cable modems and DSL modems generate 10BaseT
traffic, even if they are on a 100BaseT network.
The trash is radiated common mode by the Ethernet cables, power
cables, and also directly from unshielded enclosures. The common
mode stuff on the cables can be suppressed pretty well using
ferrite chokes as described in an applications paper and Power
Point presentation on my website.
http://audiosystemsgroup.com/publish
However -- even after you suppress your own birdies, you will hear
those of your neighbors. As it turns out, the clocks that
establish these birdies vary a bit from one piece of hardware to
another. If, for example, you tune to 14,030, you'll typically
hear 2-6 different birdies, each modulated by data, and spread by
roughly 1 kHz. What you hear strongest will depend on your
antenna, theirs (their Ethernet cables), their relative proximity,
and the relative dirtiness of their hardware.
Jim Brown K9YC
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