[RFI] Strong RFI on 2m

[Jim Brown]

On 12/22/2021 1:46 PM, nlsa at nlsa.com wrote:
> My question should be, "What does Ethernet EMI look like at VHF?"  It might be different at HF.

YES! The first step in ANY investigation of noise should be with the 
widest practical waterfall display at frequencies of interest.

http://k9yc.com/KillingReceiveNoise.pdf

At HF, wired Ethernet is radiated as a common mode signal and heard as 
multiple birdies at certain harmonics of the digital waveform. Study 
this link for a discussion of the issue, and a list of frequencies where 
many of the land in the HF bands and 6M.

http://k9yc.com/RFI-Ham.pdf

At VHF, the mechanism is different -- leakage of those components of the 
digital signal above the frequency where the tightly twisted pairs are 
no longer tight enough to resist leakage/crosstalk. I hear it as 
broadband noise in a 2M talkie close to the cable. I've not looked at 
spectrum.

Both mechanisms can be effectively suppressed by the use of shielded CAT 
cable provided that the shield is properly terminated at both ends. 
Obviously, this requires connectors with a shield contact AND proper 
termination of that shield contact within the box to the shielding 
enclosure or circuit board's reference layer(s) at the point of entry.

73, Jim K9YC