[Elecraft] K3: Are the birdies really birdies

[Jim Brown]

On 11/16/2010 4:05 PM, Kok Chen wrote:
> After fighting with Ethernet noise, I finally swapped out all the Ethernet switches in the house with ones that have metal enclosures (Netgear GS series), and replaced all UTP CAT-5 cables to STP CAT-6 cables.  The shielded switches by themselves didn't do much until I went to the STP cables.

There are two ways the noise escapes the box. One is direct radiation 
from the box. The other is common mode current on the Ethernet cable and 
sometimes even the power cable.  You can make a BIG dent in the cable 
radiation by winding multiple turns of EVERY Ethernet cable through a 
#31 or #43 ferrite core. SINGLE TURNS (BEADS) WILL NOT WORK except on 6M 
and 2M.  5-7 turns on a 2.4-in o.d. toroid is a good starting point.

Note that BOTH ENDS of any digital connection, including an  Ethernet 
connection, can produce this trash, so if the Ethernet cable is longer 
than about 0.15 wavelengths at a frequency where you hear this stuff, 
you are likely to need chokes at both ends.

The most common of the birdies coming from modems are around 14,030 kHz, 
21,052 kHz, the bottom of 10M CW, and the bottom 100 kHz or so of 6M. 
There are also some on 30M. See my RFI tutorial for a list.  I'm a CW 
guy, so those are the ones I hear. If you work SSB you get to identify 
your own. :)

Note also that each Ethernet box has its own free-running clock, so each 
box is on a different frequency.  It is very common to kill your own 
trash but still hear your neighbors. I did in my Chicago residential 
neighborhood. When chasing these birdies, kill power to your Ethernet 
box first to identify which is yours. Otherwise you'll chase your tail.

Here in CA, I have no wired Ethernet at all, doing everything on WiFi.  
Works a treat, as our friends in the UK would say.

73, Jim Brown K9YC