[RFI] 14028 to 14034 hashbirdietrash

[Jim Brown]

On Wed, 27 Jul 2005 15:17:48 -0500, Frank Brady wrote:

>Greetings,
>I've avoided this s5 to s7 noisy area at several QTHs, but now I've 
>rediscovered the joy of DX hunting recently and I hate to give up this part 
>of the 20m band.

>I've asked other hams about this and many, but not all have experienced 
this.
>I'm not looking for anything peculiar to my current (2nd floor apartment) 
>QTH because I heard it in our home and other apartments.  The same sounding 
>interference is on the low end of 30m as well - around 10.106 to 10.108.

1. I am SURE that this IS Ethernet trash.

2. I believe it is 10BaseT traffic, which can occur on a 100BaseT connection 
if there are 10BaseT cards. Many cable modem and DSL modem outputs are 
10BaseT. 

3. The trash on 30m is also Ethernet, and you will also hear it at 21.052 
and at several places on 10 m. 

4. You will hear multiple carriers with modulation on them when there is 
data transfer, and each of your neighbors will be on a slightly different 
frequency. I have wire antennas at the front and back of my city lot, and 
some carriers are stronger or weaker on each antenna, and on each band. 

5. An effective FIX for this trash is to wrap the offending Ethernet cable a 
6-8 turns around an FT-240-43 toroid AT EACH END of the Ethernet cable that 
is longer than about 5 ft, and at one end of shorter ones. That's because 
the two ends of the cable take turns talking, so the Ethernet cable radiates 
the trash as common mode. BTW -- shielding the cable will not be effective. 
(Common mode means that the cable is working as a long wire antenna. 

6. The fix above will knock the trash down by at least 3 S-units for each 
offending source (that is, each Ethernet cable that you are hearing), but 
each birdie may be the sum of trash from several cables. And the fix will 
not touch the trash that is radiated directly from an unshielded box. 

7. There may also be some common mode radiation from the power supply. 

8. Start with your own house, fix it, then move to your neighbors after 
you've had the experience with your own system. 

If you would like to read more about this, see the publications section of 
my website for a presentation on this that I gave to my local ham club. 

BTW -- some other ways to minimize it are use the shortest Ethernet cables  
possible and run as much as practical of your system (and your neighbor's 
systems) on a WiFi link. The WiFi causes no QRN or QRM, but you will need to 
cool off the Ethernet cable that connects it to a cable modem, DSL modem, 
and other wired Ethernet connections. 

73,

Jim Brown K9YC
http://audiosystemsgroup.com