[RFI] Re: Interference Database - Ether RFI

Jim Brown jim at audiosystemsgroup.com
Sat Jul 31 19:37:57 EDT 2004

DK1MAX posted a day or two ago about an interfernce database he was setting up. My 
post was a response to that.

I've not run into problems with Ethernet receiving RFI, but I certainly do hear the Ethernet on 
the the ham bands. While all of my machines have 100BaseT cards, the connection to 
routers for cable and DSL modems work at 10BaseT. That traffic seems to be the worst on 
the HF bands. 


On Sat, 31 Jul 2004 15:02:00 -0400, Martin Ewing wrote:

>Did I miss something on the list?  What database is this?  I am also 
>interested in Ethernet RFI, and I have a small article on it at 
>http://www.aa6e.net/aa6e/rfi/index.html.  If you look closely, there are 
>birdies at least every 32 kHz on 100baseT, detectable all the way up 
>into GHz territory.  Some are much worse that others, e.g., multiples of 
>25 MHz.
>I agree that ferrites help a lot, maybe 6-8 turns on a type 43 toroid 
>core.  Resonance of Ether runs at HF wavelengths can lead to problems 
>that can kill your Ethernet ports.  (I've done it with 100 Watts on 80 
>M.)  I  try to use shielded twisted pair (STP) instead of UTP.  More 
>than that, I'm mostly switching to WiFi networking around the house. 
>Martin, AA6E
>> Subject:
>> [RFI] Intereference Database
>> From:
>> "Jim Brown" <jim at audiosystemsgroup.com>
>> Date:
>> Fri, 30 Jul 2004 11:35:15 -0500
>> To:
>> "RFI List" <rfi at contesting.com>, "dk1max at darc.de" <dk1max at darc.de>
>>I think this database could be a lot more useful if it listed specific "birdie" or 
>>carrier frequencies and cross referenced to specific equipment or 
>>equipment types that produce those frequencies. 
>>For example, I've tracked down specific frequencies in several HF CW 
>>bands that are produced by the 10BaseT Ethernet gear in my office. They 
>>3511, 10106, 14029, 14030, 21052, and 28014.  I'm sure there are other 
>>frequencies associated with 10BaseT, but I'm a CW guy and this is what I've 
>>found.  :)  
>>I've also learned that much of this is radiated by the CAT5 cable as a 
>>common mode signal, and that it can be significantly attenuated by winding 
>>the CAT5 cable around a ferrite core to form a choke. 
>>Jim Brown  K9YC

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